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Bacteriocins of Erwinia carotovora Jais, Hasnah bte Md. 1982

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BACTERIOCINS OF ERWINIA CAROTOVORA by HASNAH BTE MD.^OAIS B.Sc. (Hons), U n i v e r s i t i Sains Malaysia, 1978 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES Department of Plant Science We accept t h i s t h e s i s as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA Ju l y 1982 © Hasnah Bte Md. 3 a i s , 1982 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 DE-6 (3/81) - i i i -ABSTRACT The s e n s i t i v i t y of Erwinia carotovora subsp. a t r o s e p t i c a to b a c t e r i o c i n s produced by s t r a i n s i n the common potato serogroups of E. carotovora was i n v e s t i g a t e d . B a c t e r i o c i n s produced by re p r e s e n t a t i v e s t r a i n s of the common serogroups had a c t i v i t y spectra containing s t r a i n s from one to s i x s e n s i t i v e serogroups. S i m i l a r l y , i n d i c a t o r s t r a i n s representing d i f f e r e n t serogroups showed v a r i a b l e s e n s i t i v i t y . One i n d i c a t o r s t r a i n was s e n s i t i v e to b a c t e r i o c i n s produced by only one producing s t r a i n while others were s e n s i t i v e to b a c t e r i o c i n s produced by s t r a i n s i n se v e r a l d i f f e r e n t serogroups. B a c t e r i o c i n production i n the serogroups tested was detected only from s t r a i n s that were bi o c h e m i c a l l y E_._c. subsp. carotovora (Ec c ) . S t r a i n s i n a l l four E ^ . subsp. a t r o s e p t i c a (Eca) serogroups were b a c t e r i o c i n s e n s i t i v e and non-producers. Some Ecc s t r a i n s were b a c t e r i o c i n producers and s e n s i t i v e to b a c t e r i o c i n s produced by s t r a i n s i n other serogroups. Production and s e n s i t i v i t y were not c o r r e l a t e d with the frequency of d i s t r i b u t i o n of the more common serogroups i s o l a t e d i n nature. Representative s t r a i n s i n the two most common serogroups (I and I I I ) were s e n s i t i v e to b a c t e r i o c i n s produced by re p r e s e n t a t i v e s t r a i n s i n three and s i x serogroups r e s p e c t i v e l y . S t r a i n s i n some of the l e s s common serogroups (IX, XI and XVI) were b a c t e r i o c i n producers but were not s e n s i t i v e to the b a c t e r i o c i n s produced by the re p r e s e n t a t i v e s t r a i n s t e s t e d . Thus, a r o l e f o r b a c t e r i o c i n s i n the s u r v i v a l of these s t r a i n s i n nature cannot be r u l e d out. Of the 44 serogroup XI s t r a i n s tested by the agar overlay technique, 31 were " t y p i c a l producers", 10 were " d i f f e r e n t i a l producers" and only three were "non-producers". However, b a c t e r i o c i n production i n the l a t t e r group could be detected a f t e r i n d u c t i o n with Mitomycin C but not with UV l i g h t . In the f i v e serogroups i n which s e v e r a l s t r a i n s were t e s t e d , b a c t e r i o c i n production and s e n s i t i v i t y were serogroup rather than subspecies c h a r a c t e r i s t i c s . In dual c u l t u r e s t u d i e s the s t a r t i n g r a t i o of " t y p i c a l producer" to s e n s i t i v e s t r a i n s of 1:1000 prevented detectable growth of the s e n s i t i v e s t r a i n s . By comparison a s t a r t i n g r a t i o of 100:1 with a "non-producer" s t r a i n d i d not prevent growth of the s e n s i t i v e s t r a i n s . S i m i l a r r e s u l t s were obtained when potato tuber d i s c s were.inoculated with varying s t a r t i n g r a t i o s and the population monitored a f t e r 48 h. Thus, b a c t e r i o c i n producing s t r a i n s have a s e l e c t i v e advantage when grown together i n v i t r o with the b a c t e r i o c i n s e n s i t i v e , non-producing s t r a i n s . B a c t e r i o c i n t i t r e s were enhanced by Mitomycin C in d u c t i o n and p a r t i a l p u r i f i c a t i o n . Following ammonium s u l f a t e p r e c i p i t a t i o n and u l t r a c e n t r i f u g a t i o n (150 000 x g^  f o r 90 min), b a c t e r i o c i n a c t i v i t y i n the resuspended p e l l e t was associated with p a r t i c l e s which by transm i s s i o n e l e c t r o n microscopy resembled c o n t r a c t i l e , bacteriophage t a i l - l i k e p a r t i c l e s . These p a r t i c l e s (due to t h e i r molecular s i z e ) were associated with small (« 4 mm) c l e a r zones of i n h i b i t i o n i n the spot assay t e s t s . " B a c t e r i o c i n - l i k e " a c t i v i t y i n the supernatant was resolved by gel f i l t r a t i o n i n t o three f r a c t i o n s with estimated molecular weights of 17 700, 29 500 and 224 000 D. The f i r s t two f r a c t i o n s showed lar g e (up to 20 mm) d i f f u s e zones of i n h i b i t i o n . The t h i r d f r a c t i o n showed small ( K 4 mm) c l e a r zones of i n h i b i t i o n . A l l four f r a c t i o n s had s i m i l a r a c t i v i t y spectra against r e p r e s e n t a t i v e i n d i c a t o r s t r a i n s and were produced by a l l of the serogroup XI producer s t r a i n s t e s t e d . R e l a t i v e production d i f f e r e d depending on the s t r a i n . The threshold of s e n s i t i v i t y d i splayed by the i n d i c a t o r s t r a i n s v a r i e d with the f r a c t i o n s . The resuspended p e l l e t s had the highest t i t r e s which suggested that those macromolecular b a c t e r i o c i n s were res p o n s i b l e f o r the antagonism i n i n v i t r o and p o s s i b l y i n nature. TABLE OF CONTENTS TITLE PAGE i AUTHORIZATION i i ABSTRACT i i i TABLE OF CONTENTS v i LIST OF TABLES v i i LIST OF FIGURES v i i i ACKNOWLEDGMENT i x INTRODUCTION 1 LITERATURE REVIEW 1 A. B a c t e r i o c i n s 1 B. B a c t e r i o c i n Production by Pl a n t Pathogens 6 MATERIALS AND METHODS 15 A. B a c t e r i a l Cultures Used 15 B. Screening and Detection 15 C. P a r t i a l P u r i f i c a t i o n 17 D. E l e c t r o n Microscopy 20 E. Dual Culture Studies 21 RESULTS 23 A. Screening and Detection 23 B. P a r t i a l P u r i f i c a t i o n . 32 C. Antagonism i n Dual Cultures hi DISCUSSION hb A. Screening and Detection hb B. P a r t i a l P u r i f i c a t i o n 51 C. Dual Cul t u r e Studies 53 SUMMARY 55 LITERATURE CITED 56 LIST OF TABLES Table 1. S e n s i t i v i t y to and production of b a c t e r i o c i n s by s t r a i n s of the predominant potato serogroups of Erwinia carotovora i n B r i t i s h Columbia 24 Table 2, Table 3. Table 4. S e n s i t i v i t y of sel e c t e d s t r a i n s of four E r w i n i a  carotovora subsp. a t r o s e p t i c a serogroups to b a c t e r i o c i n s produced by s t r a i n s of Erw i n i a  carotovora subsp. carotovora serogroup XI i s o l a t e d from potato i n B r i t i s h Columbia B a c t e r i o c i n a c t i v i t y of s t r a i n s of E r w i n i a  carotovora subsp. carotovora serogroup XI' when induced with UV l i g h t and Mitomycin C as detected i n the spot assay technique by s e n s i t i v e s t r a i n s corresponding to four serogroups of Erw i n i a  carotovora subsp. a t r o s e p t i c a  Degree of i n h i b i t i o n of s e l e c t e d s t r a i n s of Erwinia  carotovora subsp. a t r o s e p t i c a by b a c t e r i o c i n -producing s t r a i n s of Erwinia carotovora subsp. carotovora serogroup XI 26 27 28 Table 5. R e c i p r o c a l d i l u t i o n end-point at which a c t i v i t y could be detected by the spot assay technique i n broth c u l t u r e f i l t r a t e s of non-induced and induced producer s t r a i n s of Erwinia carotovora subsp. carotovora serogroup XI 30 Table 6. Table 7. Table 8. Reci p r o c a l d i l u t i o n end-point at which a c t i v i t y could be detected i n broth c u l t u r e f i l t r a t e s of non-induced and induced producer s t r a i n s of Erw i n i a carotovora subsp. carotovora serogroup XI when induced with d i f f e r e n t concentrations of Mitomycin C , Re c i p r o c a l d i l u t i o n end-point at which a c t i v i t y could be detected by the spot assay technique i n d i f f e r e n t f r a c t i o n s of p a r t i a l l y p u r i f i e d b a c t e r i o c i n preparations Detection of s e n s i t i v e s t r a i n s of E r w i n i a  carotovora subsp. a t r o s e p t i c a a f t e r 48 h incubation i n dual broth c u l t u r e s with d i f f e r e n t s t a r t i n g r a t i o s of Erw i n i a carotovora subsp. carotovora serogroup XI 31 33 41 Table 9. Detection of s e n s i t i v e s t r a i n s of E r w i n i a carotovora subsp. a t r o s e p t i c a i n potato d i s c s 48 h a f t e r i n o c u l a t i o n with mixed c u l t u r e s containing d i f f e r e n t s t a r t i n g r a t i o s of Erw i n i a carotovora subsp. carotovora serogroup X I . . . . . LIST OF FIGURES Figure 1. Flow chart f o r p a r t i a l p u r i f i c a t i o n of b a c t e r i o c i n from Erwinia carotovora 19 Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. B a c t e r i o c i n a c t i v i t y against i n d i c a t o r s t r a i n s of Erwinia carotovora subsp. a t r o s e p t i c a i n t h r e e - f o l d d i l u t i o n % e r i e s (counter-clockwise) from Mitomycin C induced c u l t u r e f i l t r a t e s of Er w i n i a carotovora subsp. carotovora s t r a i n s at d i f f e r e n t stages i n p u r i f i c a t i o n 34 B a c t e r i o c i n a c t i v i t y (detected by i n d i c a t o r s t r a i n 504) i n the p a r t i a l l y p u r i f i e d "high-speed" supernatant ( s t r a i n 379) a f t e r f r a c t i o n a t i o n on a Sephacryl S-300 column 36 R e l a t i v e b a c t e r i o l y t i c a c t i v i t y (detected by i n d i c a t o r s t r a i n 504) i n f r a c t i o n s 33 to 46 obtained when the p a r t i a l l y p u r i f i e d high speed supernatant from producer s t r a i n 379 was run on a Sephacryl S-300 column 38 Standard curve of Kav Vs log molecular weight p l o t t e d using p r o t e i n of known molecular weights ( a p o f e r r i t i n , c a t a l a s e , phosphorylase B and cytochrome C) determined from gel f i l t r a t i o n (Sephacryl S-300). (A) i n d i c a t e s Kav Vs l o g molecular weight of the b a c t e r i o c i n - l i k e component at f r a c t i o n #19, at f r a c t i o n #37 (B) and at f r a c t i o n #41 (C) 39 E l e c t r o n micrograph of resuspended high speed p e l l e t f r a c t i o n from E_. carotovora s t r a i n s 379 (A) and 440 (B) 40 Growth curves f o r s t r a i n s 379 and 626 (Erwinia  carotovora subsp. carotovora) and s t r a i n 530 (Erw i n i a carotovora subsp. a t r o s e p t i c a ) i n n u t r i e n t broth at two d i f f e r e n t temperatures 43 ACKNOWLEDGMENT I wish to thank my sup e r v i s o r , Dr. R.3. Copeman f o r h i s e s s e n t i a l guidance, suggestions and c r i t i c a l readings p e r t a i n i n g to the completion of t h i s t h e s i s . Thanks are also due f o r t h e i r h e l p f u l suggestions to the other members of my graduate committee which included Dr. S.H. De Boer, A g r i -c u l t u r e Canada and Dr. V.C. Runeckles, Department of Pla n t Science. Thanks are extended to Dr. A. Greenland, Department of Pl a n t Science f o r a s s i s t a n c e i n gel f i l t r a t i o n experiments. I a l s o wish to thank Ms. B. Schroeder f o r as s i s t a n c e with the e l e c t r o n microscopy. I g r a t e f u l l y acknowledge the f i n a n c i a l support of the Malaysian government throughout my s t u d i e s . INTRODUCTION Er w i n i a carotovora (Oones) Bergey jst a l . i s an important b a c t e r i a l pathogen of potato causing the diseases s o f t r o t and b l a c k l e g . Since chemical c o n t r o l s have not proven e f f e c t i v e , current c o n t r o l programmes are almost e x c l u s i v e l y based on s a n i t a t i o n and c u l t u r a l p r a c t i c e s (Agrios 1978). A thorough knowledge of the ecology and population dynamics of the b a c t e r i a i n nature i s required f o r t h i s approach to be s u c c e s s f u l . One aspect of the ecology of the s o f t r o t t i n g erwinias deserving more a t t e n t i o n i s the a b i l i t y to produce b a c t e r i o c i n s . The s e l e c t i v e advantage conferred on producing s t r a i n s may be a f a c t o r i n e x p l a i n i n g the prevalence of c e r t a i n s t r a i n s i n nature. I t may also represent a mechanism that could be manipulated f o r the purpose of b i o l o g i c a l c o n t r o l . LITERATURE REVIEW A. B a c t e r i o c i n s G r a t i a (1925) f i r s t described a h i g h l y s p e c i f i c a n t i - b a c t e r i a l compound produced by a s t r a i n of E_. c o l i . This compound named " C o l i c i n e " was a c t i v e against only s t r a i n s of the same species ( G r a t i a and F r e d e r i c q 1946). A more general term " b a c t e r i o c i n e " was proposed by Jacob et a l . (1953) with the discovery of s i m i l a r compounds i n organisms other than the c o l i f o r m s . This term i s now s p e l l e d " b a c t e r i o c i n " without the f i n a l "e" (Mayr-Harting et a l . 1972). Compounds with s i m i l a r p r o p e r t i e s have been described as being produced by B a c i l l u s megaterium de Barry (megacins), by C l o s t r i d i u m spp. Prazmowski ( c l o s t o c i n s ) , by Streptococcus spp. Rosenbach ( s t r e p t o c o c c i c ) , by Staphycococcus Rosenbach ( s t a p h y l o c o c c i c ) and many more (Tagg et a l . 1976). Based on work done on the b a c t e r i o c i n s produced by E. c o l i , (Migula) C a s t e l l a n i and Chalmers, Nomura (1967) defined b a c t e r i o c i n s as n o n - r e p l i c a t i n g , b a c t e r i c i d a l , p r o t e i n - c o n t a i n i n g substances which are produced by c e r t a i n s t r a i n s and which are a c t i v e on the same or c l o s e l y r e l a t e d species. The requirement f o r having receptor s i t e s i s important i n d i s t i n g u i s h i n g b a c t e r i o c i n s from l e s s s p e c i f i c a n t i b i o t i c s . In the l a t e s t review Tagg et a l . (1976) l i s t e d the f o l l o w i n g s i x c r i t e r i a that have been used with varying degrees of consistency i n d e f i n i n g b a c t e r i o c i n s : i . B a c t e r i o c i n s have a narrow range of i n h i b i t o r y a c t i v i t y centered about the homologous species, i i . B a c t e r i o c i n s have an e s s e n t i a l b i o l o g i c a l l y a c t i v e p r o t e i n moeity. i i i . B a c t e r i o c i n s have a b a c t e r i c i d a l mode of a c t i o n , i v . B a c t e r i o c i n s show attachment to s p e c i f i c receptor s i t e s , v. The genetic determinant of b a c t e r i o c i n s i s plasmid-borne ( i n terms of production and host immunity), v i . Production of b a c t e r i o c i n s i s by l e t h a l b i o s y n t h e s i s . C r i t e r i a i , i i and i i i are g e n e r a l l y a p p l i c a b l e f o r many of the bet t e r c h a r a c t e r i z e d b a c t e r i o c i n s . C r i t e r i a i v and v have not been documented f o r many b a c t e r i o c i n s . C r i t e r i a v i has only been shown f o r i n d u c i b l e b a c t e r i o c i n s . Because there i s no u n i v e r s a l l y accepted d e f i n i t i o n f o r b a c t e r i o c i n s and many a n t i b a c t e r i a l compounds have not been adequately c h a r a c t e r i z e d , Tagg et a l . (1976) suggested that incompletely defined a n t a g o n i s t i c substances be designated " b a c t e r i o c i n - l i k e " . They reserved the term " b a c t e r i o c i n s " f o r those a n t i b a c t e r i a l compounds f u l f i l l i n g at l e a s t c r i t e r i a i i and i i i as noted above. By t h i s d e f i n i t i o n a wide range of heterogenous substances are i n c l u d e d . For example Stre p t o c o c c i n A-FF22 (Tagg et a l . 1973) with a molecular weight of 8000 D, B o t i c i n S-5 ( c o n s i s t i n g of bacteriophage t a i l - l i k e p a r t i c l e s ) with a molecular weight of 4 x 10 D produced by C l o s t r i d i u m botulinum Van Ermergen ( E l l i s o n and Kautter 1970) and the k i l l e r p a r t i c l e s produced by B a c i l l u s spp. (Ackermann 1973) are a l l i n c l u d e d . The l a t t e r resemble i n t a c t b a c t e r i o p h a g e - l i k e p a r t i c l e s but are not able to m u l t i p l y w i t h i n the s e n s i t i v e c e l l s . Bradley (1967) c l a s s i f i e d b a c t e r i o c i n s i n t o two major groups. The f i r s t c o n s i s t s of low molecular weight compounds, non-sedimentable by high speed c e n t r i f u g a t i o n which are t r y p s i n s e n s i t i v e , heat r e s i s t a n t and not resolved by e l e c t r o n microscopy. The second group contains high molecular weight compounds having the opposite c h a r a c t e r i s t i c s . The ma j o r i t y of b a c t e r i o c i n s are complex molecules c o n t a i n i n g p r o t e i n , l i p i d and carbohydrate components (Tagg et ^1_. 1976; B a l l e s t e r et aL. 1980). Stre p t o c o c c i n STH, produced by transformable group H Streptococcus spp., i s a complex molecule c o n t a i n i n g the e s s e n t i a l p r o t e i n component plus l i p i d and phosphate groups (Schlegel and Slade 1972). B a c t e r i o c i n s produced by two C l o s t r i d i u m spp. appear to be p r i m a r i l y p r o t e i n i n nature (Clarke et a l . 1975). S e n s i t i v i t y to s p e c i f i c enzymes such as proteinase, l i p a s e , e t c . have been widely used to i d e n t i f y e s s e n t i a l chemical components of b a c t e r i o c i n s . However, caution i n i n t e r p r e t a t i o n i s required because Hamon and Peron (1964) noted that p r o t e o l y t i c enzyme producers f r e q u e n t l y produced b a c t e r i o c i n s r e s i s t a n t to these enzymes. Conversely, b a c t e r i o c i n s produced by n o n - p r o t e o l y t i c b a c t e r i a are s u s c e p t i b l e to p r o t e o l y t i c enzymes. Since the b i o l o g i c a l l y - e s s e n t i a l component i s p r o t e i n , b a c t e r i o c i n s might be expected to be good antigens. In f a c t a n t i g e n i c d i f f e r e n c e s between four b a c t e r i o c i n s produced by C l o s t r i d i u m  p e r f r i n g e n s ( V e i l l o n and Zuber) Hauduray et j a l . i n double d i f f u s i o n t e s t s have been reported (Tubylewicz 1970). Two pyocins with d i f f e r e n t a c t i v i t y s p e c t r a , i s o l a t e d from Pseudomonas aeruginosa (Schroeter) Migula d i f f e r s e r o l o g i c a l l y (Govan 1974). A n t i s e r a against b a c t e r i o c i n s may be u s e f u l i n b a c t e r i o c i n c l a s s i f i c a t i o n , i n d i s t i n g u i s h i n g between components of complex b a c t e r i o c i n s and i n e l i m i n a t i n g b a c t e r i o c i n s when searching f o r l y s o g e n i c phage (Hamon 1956). However the f a i l u r e to produce antiserum against b a c t e r i o c i n s produced by Staphylococcus aureus Rosenbach has been noted by Gagliano and H i n s d i l l (1970) and Hale and H i n d s d i l l (1973). The receptor s i t e s f o r c o l i c i n s E3-CA38 (Sabet and Schnaitman 1973) and c o l i c i n M-K12 (Braun et a l . 1973, 1974; Braun and Wolff 1973) have been i d e n t i f i e d as a p r o t e i n i n the outer membrane. This receptor s i t e was also shown to be the receptor s i t e f o r T5 phage. The receptor s i t e s f o r c o l i c i n E may also be the receptor s i t e s f o r bacteriophage BF23 and Vitamin B12 (Buxton 1971 and Di Masi et a l . 1973). In other s t u d i e s the l i p o p o l y s a c c h a r i d e (LPS) component has been regarded as the c o l i c i n B receptor s i t e (Guterman and L u r i a 1969). S i m i l a r l y the LPS component of the c e l l envelope was also regarded as the receptor s i t e f o r pyocin R, a b a c t e r i o c i n produced from Pseudomonas aeruginosa (Ikeda and Egami 1973). Various modes of ac t i o n have been proposed f o r the c o l i c i n s . C o l i c i n s E1 and K, appear to act on the cytoplasmic membrane, i n h i b i t i n g ATP production, membrane tra n s p o r t and p e r m e a b i l i t y . The l o s s of K + ion from c o l i c i n - t r e a t e d c e l l s was noted (Broda 1979). C o l i c i n E2 has been regarded as a DNA endonuclease which degrades DNA and i n h i b i t s c e l l d i v i s i o n (Nomura 1963; S c h a l l e r and Nomura 1976) presumably a f t e r e n t e r i n g the c e l l , on the other hand, c o l i c i n E3 appears to act as an RNase c l e a r i n g the 16-S ribosomal RNA and hence prevent p r o t e i n s y n t h e s i s . (Bowman et a l . 1971; Senior and Holland 1971). With both c o l i c i n s E2 and E3 degradation occured _in_ v i t r o a f t e r the removal of a s p e c i f i c "immunity p r o t e i n " which forms a t i g h t complex with the b a c t e r i o c i n s . This "immunity p r o t e i n " was also coded by the c o l i c i n o g e n i c f a c t o r i t s e l f . I t i s not w e l l e s t a b l i s h e d whether the l e t h a l a c t i o n of c o l i c i n E2 and E3 i s due to d i r e c t enzymatic a c t i o n or a c t i v a t i o n of some endogenous enzymes r e s i d i n g i n the s e n s i t i v e c e l l s . The r o l e of b a c t e r i o c i n s i n nature may be associated with the r e g u l a t i o n of population dynamics. V i r i d i n s , b a c t e r i o c i n s of alpha-hemolytic s t r e p t o c o c c i l i v i n g as a component of normal m i c r o f l o r a of the t h r o a t , have been suggested as being res p o n s i b l e f o r r e s i s t a n c e to i n f e c t i o n by group A s t r e p t o c o c c i (Dajani et a l . 1976). When ba c t e r i o c i n o g e n i c Staphylococcus aureus s t r a i n s were ino c u l a t e d with group A s t r e p t o c o c c i i n mixed s k i n i n f e c t i o n s on hamster, the l a t t e r was el i m i n a t e d or reduced s i g n i f i c a n t l y (Dajani and Wannamaker 1973). However, some other attempts to demonstrate that b a c t e r i o c i n s may play a major r o l e i n the r e g u l a t i o n of the b a c t e r i a l populations have been u n s u c c e s s f u l . K e l s t r u p and Gibbon (1969) reported that b a c t e r i o c i n s probably do not play a major re g u l a t o r y r o l e i n b a c t e r i a l populations forming dental plaque because s t r e p t o c o c c a l b a c t e r i o c i n s were i n a c t i v a t e d by the enzyme protease found i n the o r a l c a v i t y . Also both b a c t e r i o c i n producer as w e l l as s e n s i t i v e s t r a i n s have been recovered simultaneously i n the same samples. The presence of matrix polysaccharide probably masks the receptor s i t e s hence enabling the escape of s e n s i t i v e s t r a i n s from the b a c t e r i o c i n - p r o d u c i n g s t r a i n s of Streptococcus spp. (Rogers 1974). B. B a c t e r i o c i n Production by P l a n t Pathogens Species of four genera of plant pathogenic b a c t e r i a have been reported to produce b a c t e r i o c i n s . However, only a few species have been c h a r a c t e r i z e d and p u r i f i e d . Vidaver (1972) reported d i f f e r e n t i a l b a c t e r i o c i n production and s e n s i t i v i t y among three Pseudomonas spp. A l l 38 s t r a i n s of P^ . syringae {P_. syringae pv. syringae Van H a l l ) produced b a c t e r i o c i n s having a broad a c t i v i t y s p e c t r a . Only 55% of 24 s t r a i n s of _P. g l y c i n e a (P. syringae pv. g l y c i n e a Van H a l l ) produced b a c t e r i o c i n s and these had a more r e s t r i c t e d a c t i v i t y spectrum than those of P_. syringae. Only 8% of 39 s t r a i n s of _P. p h a s e o l i c o l a (JP. syringae p v . p h a s e o l i c o l a (Burkholder) Young et al_.) produced b a c t e r i o c i n s and these had the narrowest range of a c t i v i t y . B a c t e r i o c i n s e n s i t i v i t y to heat and t r y p s i n v a r i e d so that not a l l conformed to Bradley's (1967) c l a s s i f i c a t i o n . B a c t e r i o c i n s produced by P_. syringae s t r a i n 4-A (Haag and Vidaver 1974) and s t r a i n W-1 (Smidt and Vidaver 1981) have been p u r i f i e d and c h a r a c t e r i z e d . Both b a c t e r i o c i n s appear to be s i m i l a r i n that they are high molecular weight bacteriophage t a i l - l i k e p a r t i c l e s which are heat s e n s i t i v e and t r y p s i n r e s i s t a n t . The molecular weight of s y r i n g a c i n 4~A 7 was determined to be 1.6 x 10 D. Production was enhanced by UV l i g h t or Mitomycin C and the product sedimented as a s i n g l e component i n u l t r a c e n t r i f u g a t i o n . The major composition of s y r i n g a c i n 4—A was p r o t e i n . Vidaver (1976) reported that when soybean seeds were tre a t e d with s y r i n g a c i n 4—A, p r i o r to challenge i n o c u l a t i o n with P_. g l y c i n e a the c o n t r o l (without b a c t e r i o c i n p r o t e c t i o n ) had 20% l e s s germination. Lesion counts on bean leaves were al s o s i g n i f i c a n t l y reduced when p u r i f i e d s y r i n g a c i n 4--A was sprayed p r i o r to challenge i n o c u l a t i o n with P_. p h a s e o l i c o l a . Whether t h i s treatment w i l l be s u c c e s s f u l on a f i e l d s c a l e has yet to be determined. B a c t e r i o c i n production by P^ . solanacearum (Smith) Smith has a l s o been reported by Cuppels ^ t j d . (1978). The b a c t e r i o c i n was i s o l a t e d and c h a r a c t e r i z e d from an a v i r u l e n t form of s t r a i n K-60 named s t r a i n B1 S e n s i t i v i t y to t h i s b a c t e r i o c i n was noted i n 43 of 51 i n d i c a t o r s t r a i n s . B a c t e r i o c i n production was enhanced ten f o l d by exposure to UV l i g h t but Mitomycin C (at a f i n a l c oncentration of 1 mg/ml or other chemical reagents (chloramphenicol or trimethorprim) caused only a doubling. The optimal temperature f o r b a c t e r i o c i n production was recorded as 30° C whereas the optimal growth temperature of the bacterium was 32° C. The b a c t e r i o c i n had an approximate molecular weight of 65 000 D, was sedimentable and r e s i s t a n t to enzymes. These c h a r a c t e r i s t i c s conformed to Bradley's (1967) low molecular weight group. (Chen and Echandi 1981) reported that seedling roots soaked i n suspensions of an a v i r u l e n t , b a c t e r i o c i n - p r o d u c i n g s t r a i n conferred a high degree of p r o t e c t i o n against the v i r u l e n t s t r a i n i n greenhouse t e s t s . Three s e n s i t i v e s t r a i n s known to have a wide spectrum of s e n s i t i v i t y to bacte r i o c i n - p r o d u c i n g s t r a i n s of P_. solanacearum have been employed as i n d i c a t o r s t r a i n s to detect unknown bac t e r i o c i n - p r o d u c i n g s t r a i n s i n s e r i a l d i l u t i o n s of North C a r o l i n a s o i l samples (Chen and Echandi 1982). The technique was reported to be s u c c e s s f u l f o r d e t e c t i o n and q u a n t i f i c a t i o n of P^ . solanacearum, i n v i t r o as w e l l as i n the s o i l samples c o l l e c t e d from the f i e l d s . The usefulness of t h i s technique depends on two p r e r e q u i s i t e f a c t o r s namely, reduction of other s o i l b a c t e r i a and fungi (hence the use of s e n s i t i v e s e l e c t i v e media) and the presence of wide spectrum i n d i c a t o r s t r a i n s . However, t h i s technique w i l l not be able to detect s t r a i n s that are not producing b a c t e r i o c i n s or producing b a c t e r i o c i n s to which the i n d i c a t o r s are not s e n s i t i v e . Production of b a c t e r i o c i n s by Corynebacterium michiganense (now C. michiganense pv. michiganense (Smith) Gensen) has been shown i n 55 of 96 s t r a i n s t e s t e d (Echandi 1976). The d i f f u s e i n h i b i t i o n zones, enzyme s e n s i t i v i t y and heat s t a b i l i t y of b a c t e r i o c i n s produced by four r e p r e s e n t a t i v e s t r a i n s suggest that b a c t e r i o c i n s corresponding to Bradley's (1967) low molecular weight group are i n v o l v e d . A t y p i n g scheme based on the s e n s i t i v i t y pattern of the i n d i c a t o r s t r a i n s enabled typing of 90% of the s t r a i n s i n t o 10 groups. Gross and Vidaver (1979) found that the ma j o r i t y of b a c t e r i o c i n s produced by species i n the genus Corynebacterium were b a c t e r i c i d a l p r o t e i n s , r e s i s t a n t to heat (75 - 80°C f o r 30 min ) and s e n s i t i v e to p r o t e o l y t i c enzymes. C. nebraskense (Schuster et ) Dye and Kemp, C_. michiganense and flaccumfaciens (Hedges) Dowson and Hedges produced two b a c t e r i o c i n s which were d i f f e r e n t i a t e d on the basis of heat s e n s i t i v i t y , s u s c e p t i b i l i t y to protease, c o n d i t i o n s f o r production and spectrum of a c t i v i t y . A b a c t e r i o c i n produced by jC. michiganense s t r a i n 15-2 has been p u r i f i e d and c h a r a c t e r i z e d (Huang and Echandi 1981). The b a c t e r i o c i n was found to be t r y p s i n s e n s i t i v e and heat l a b i l e (80°C f o r 15 min.) with bacteriophage t a i l - l i k e morphology under e l e c t r o n microscopy. Crude b a c t e r i o c i n preparations i s o l a t e d from C_. michiganense have been shown to be p r o t e c t i v e against b a c t e r i a l canker on tomato seedlings i n greenhouse experiments (Echandi 1975). Since only crude preparations were used, confirmation using the p u r i f i e d b a c t e r i o c i n preparations would be d e s i r a b l e . The best known b a c t e r i o c i n associated with plant pathogenic b a c t e r i a i s agrocin 84 produced by the non-pathogenic, b a c t e r i o c i n producing s t r a i n 84 of Agrobacterium radiobacter pv. radiobacter Keane et_ al_. and a c t i v e against the pathogenic form of A_. radiobacter pv. tumefaciens Keane et a l . (New and Kerr 1972; Kerr and Htay 1974). The b a c t e r i o c i n was i d e n t i f i e d as a low molecular weight, 6-N-phosphoramidate of an adenine nucleotide analogue (Roberts et _ a l . 1977). Since there i s no b i o l o g i c a l l y a c t i v e p r o t e i n moeity i n t h i s b a c t e r i o c i n , i t may w e l l represent a new type; the nucleotide b a c t e r i o c i n s (Kerr 1980). Bothproduction and immunity are coded f o r by t r a n s f e r a b l e plasmids of 6 6 high molecular weight, 30 x 10 D and 124 x 10 D r e s p e c t i v e l y (Sciaky et a l . 1977) . The agrocin 84 producer a l s o possesses another plasmid that codes f o r u t i l i z a t i o n of nopaline, an unusual amino a c i d only o c c u r r i n g i n crown g a l l t i s s u e s . Kerr (1980) reported that on i t s own the plasmid that confers agrocin 84 production and immunity i s not conjugative but the plasmid that codes f o r the u t i l i z a t i o n of nopaline can promote conjugation by m o b i l i z i n g the agrocin plasmid making i t t r a n s f e r a b l e ( E l l i s and Kerr 1978). A l a r g e plasmid ( T i plasmid) was found to code f o r pathogenicity (Van Larebeke et a l . 1975; Watson et a^. 1975). The gene c o n t r o l l i n g agrocin s e n s i t i v i t y was also located i n t h i s plasmid (Engler et a l . 1975). The a b i l i t y of transconjugation between non-pathogenic, agrocin-producing and pathogenic forms of Agrobacterium has been shown i n v i t r o (Kerr 1980). The conjugants have the p o s s i b i l i t y of having both p r o p e r t i e s , the a b i l i t y to produce b a c t e r i o c i n as w e l l as being pathogenic or being both pathogenic and r e s i s t a n t to agrocin 84. The presence of nopaline (as a promoter) i n g a l l e d t i s s u e s i s a p r e r e q u i s i t e for t r a n s c o n j u g a t i o n . The use of agrocin 84 i n b i o l o g i c a l c o n t r o l programmes f o r crown g a l l has been very s u c c e s s f u l i n a v a r i e t y of crops i n the rosaceae world-wide (Moore and Warren 1979) . B i o l o g i c a l c o n t r o l was p o s s i b l e when a r a t i o of at l e a s t 1:1 of non-pathogen, agrocin producer to pathogen was employed (New and Kerr 1972). Seedlings or c u t t i n g s were soaked i n suspensions of _A. radiobacter s t r a i n 84 before p l a n t i n g . In a few cases, f o r example i n Greece, a breakdown i n c o n t r o l has been c i t e d probably due to the a b i l i t y f o r plasmid t r a n s f e r i n the presence of already g a l l e d t i s s u e s (Kerr 1980). However i n A u s t r a l i a l i t t l e or no plasmid t r a n s f e r appears to have occurred. This may be due to the f a c t that l i t t l e or no g a l l i n g has occurred, r e s u l t i n g i n no a v a i l a b l e nopaline as a promoter. Moore (1976) reported that l a t e n t i n f e c t i o n r e s u l t e d i n 24-36% r e s i s t a n c e to agrocin 84 i n the United S t a t e s . Obviously the use of healthy seedlings or c u t t i n g s i n o c u l a t e d with A. r a d i o b a c t e r s t r a i n 84 i s important to ensure e f f e c t i v e b i o l o g i c a l c o n t r o l . A mutant s t r a i n 84 with a d e f e c t i v e a b i l i t y f o r plasmid t r a n s f e r would be an i d e a l antagonist as i t would avoid the p o s s i b i l i t y of t r a n s c o n j u g a t i o n . In the genus E r w i n i a , b a c t e r i o c i n s from at l e a s t three species have been i n v e s t i g a t e d . B a c t e r i o c i n production from E. carotovora was f i r s t shown by Hamon and Peron (1961). Later Endo _et ^ 1 . (1975) and Kamimiya et_ a l . (1977) showed b a c t e r i o c i n a c t i v i t y i n the p e l l e t f r a c t i o n of c u l t u r e f i l t r a t e s a f t e r u l t r a c e n t r i f u g a t i o n (105 000 x j j f o r 60 min „). Bacteriophage t a i l - l i k e p a r t i c l e s were observed i n the p a r t i a l l y p u r i f i e d preparations. These macromolecular b a c t e r i o c i n s were f u r t h e r p u r i f i e d and c h a r a c t e r i z e d by Itoh et a^. (1978). B a c t e r i o c i n a c t i v i t y was recovered completely i n the p e l l e t f r a c t i o n a f t e r u l t r a c e n t r i f u g a t i o n (100 000 x g_ f o r 60 min ). C a r o t o v o r i c i n Er production was only detected a f t e r i n d u c t i o n with Mitomycin C. The b a c t e r i o c i n was r e s i s t a n t to various p r o t e o l y t i c enzymes but was completely destroyed by heat treatment (80°C f o r 10 min ). Echandi and Moyer (1979) showed that two s t r a i n s of E. chrysanthemi also produced b a c t e r i o c i n s with bacteriophage t a i l - l i k e p a r t i c l e s composed of c o n t r a c t i l e sheaths and cores. Loose cores and empty sheaths were a l s o observed. However, b a c t e r i o c i n production was spontaneous and enhanced with UV l i g h t or Mitomycin C i n d u c t i o n . On the basis of heat and enzyme s e n s i t i v i t y two types of b a c t e r i o c i n s produced by two d i f f e r e n t s t r a i n s of E. carotovora were d i s t i n g u i s h e d (Echandi 1976). Campbell and Echandi (1979) p a r t i a l l y p u r i f i e d two b a c t e r i o c i n s which were d i s t i n g u i s h a b l e by agar d i f f u s i b i l i t y and u l t r a c e n t r i f u g a t i o n . The one showing s m a l l , c l e a r i n h i b i t i o n zones was found to c o n s i s t of bacteriophage t a i l - l i k e p a r t i c l e s by e l e c t r o n microscopy. The one producing l a r g e r and d i f f u s e i n h i b i t i o n zones was not studied f u r t h e r . A s i m i l a r p a r t i c l e s t r u c t u r e was confirmed by Crowley and De Boer (1980) f o r a b a c t e r i o c i n produced by another s t r a i n of Erwinia carotovora. They noted that a low molecular weight b a c t e r i o c i n was probably present together with the high molecular weight type produced by a s t r a i n i n serogroup X based on agar d i f f u s i b i l i t y . The observation was not f u r t h e r i n v e s t i g a t e d . When s e m i - p u r i f i e d b a c t e r i o c i n preparations of E_. carotovora were a p p l i e d p r i o r to challenge i n o c u l a t i o n with the pathogen, potato s l i c e s were protected from s o f t rot (Campbell and Echandi 1979). However p r o t e c t i o n was not observed when n a t u r a l l y - i n f e s t e d tubers were t e s t e d . No explanation f o r t h i s f a i l u r e was given. However, i t i s probable that the b a c t e r i a n a t u r a l l y i n f e s t i n g the tubers were not s e n s i t i v e to the se m i - p u r i f i e d b a c t e r i o c i n p r e p a r a t i o n . In v i t r o s t u d i e s by Beer (1981) have shown that a non-pathogen, b a c t e r i o c i n producing s t r a i n of El. h e r b i c o l a i n h i b i t s the growth of E_. amylovora. When l i v i n g b a c t e r i a were employed, the degree of c o n t r o l was d i r e c t l y r e l a t e d to the b a c t e r i a l concentration used. When b a c t e r i o c i n preparations were used, disease incidence was g r e a t l y decreased (Beer 1981). Itoh et a l . (1980a, 1980b and 1981) have r e c e n t l y proposed the mode of a c t i o n f o r c a r o t o v o r i c i n Er. L y s i s of the s e n s i t i v e c e l l s was apparently due to degradation of the membrane phospholipid. This degradation was caused mainly by the a c t i v i t y of phospholipase A, an endogenous enzyme found i n the s e n s i t i v e c e l l s . This enzyme seemed to be a c t i v a t e d from a l a t e n t form by the a c t i o n of the b a c t e r i o c i n . However, a phospholipase A d e f i c i e n t mutant s t i l l r e t a i n e d binding to c a r o t o v o r i c i n Er but was not l y s e d . This i n d i c a t e d that adsorption of b a c t e r i o c i n to the receptor s i t e s i s an i n i t i a l step leading to c e l l death.The presence of phospholipase A i n the s e n s i t i v e c e l l s i s required f o r l y s i s but how binding of b a c t e r i o c i n s a c t i v a t e s l y s i s i s unknown. As noted above with Agrobacterium spp., production of b a c t e r i o c i n s may play a s i g n i f i c a n t r o l e i n r e g u l a t i n g the population dynamics of c l o s e l y r e l a t e d s p e cies. The few _in_ v i t r o s tudies with E_. carotovora also suggest that the b a c t e r i o c i n producing s t r a i n s have a s e l e c t i v e advantage over the s e n s i t i v e , non-producing s t r a i n s . Recently a serotyping scheme f o r E. carotovora has been e s t a b l i s h e d by De Boer et a l . (1979) based on the d i f f u s i b l e somatic antigen. Using t h i s scheme they noted that c e r t a i n serogroups ( I , I I I , IX, XI and XVI) are more commonly found i n nature than others. Among s t r a i n s of E_. carotovora subsp. a t r o s e p t i c a (Van H a l l ) Dye (Eca), those belonging to serogroup I are predominantly found associated with potato i n B r i t i s h Columbia (Dr. R.3. Copeman, personal communication) compared to those i n serogroups X V I I I , XX and X X I I ) . This p r o j e c t was undertaken to determine whether b a c t e r i o c i n production and s e n s i t i v i t y i s a f a c t o r i n the population dynamics and d i s t r i b u t i o n of s t r a i n s of J£. carotovora i n nature. The f o l l o w i n g s p e c i f i c o b j e c t i v e s were i d e n t i f i e d : To determine whether b a c t e r i o c i n production and s e n s i t i v i t y i s c o r r e l a t e d to the frequency of d i s t r i b u t i o n of the v a r i o u s serogroups i n nature. To determine whether ba c t e r i o c i n - p r o d u c i n g s t r a i n s are a n t a g o n i s t i c to the s e n s i t i v e s t r a i n s i n mixed c u l t u r e s t u d i e s and on potato d i s c s . To determine i f more than one b a c t e r i o c i n i s produced and to determine whether there are d i f f e r e n c e s i n c o n c e n t r a t i o n , type and a c t i v i t y . MATERIALS AND METHODS A. B a c t e r i a l C u l t u r e s Used A l l s t r a i n s except SR8 of E_. carotovora (see t a b l e s 1 and 2) used i n these s t u d i e s were o r i g i n a l l y i s o l a t e d by Dr. R.3. Copeman from potatoes grown i n B r i t i s h Columbia. Stock c u l t u r e s had been maintained at 4°C f o r 3 to 5 years on n u t r i e n t agar s l a n t s i n screw-capped tubes. Working stock c u l t u r e s f o r r o u t i n e use were maintained as t u r b i d b a c t e r i a l suspensions ( A ^ o * D i n d i s t i l l e d water at 4°C and renewed every 4 months. S t r a i n s were r o u t i n e l y streaked from the working stock c u l t u r e s onto n u t r i e n t agar p l a t e s and incubated f o r 48 h at 26°C. B a c t e r i a l suspensions or c o l o n i e s from these 48 h c u l t u r e s were incubated at 26°C. B. Screening and Detection B a c t e r i o c i n a c t i v i t y was detected by the modified agar overlay technique (Crowley and De Boer 1980). Test s t r a i n s were stab i n o c u l a t e d i n t o n u t r i e n t agar p l a t e s . The stab i n o c u l a t i o n technique was used i n the p r e l i m i n a r y screening and det e c t i o n of the various s t r a i n s i n serogroups while i n subsequent s t u d i e s the r e p l i c a p l a t i n g technique was used. A f t e r 48 h incubation at 26°C, d u p l i c a t e r e p l i c a p l a t e s were prepared f o r each t e s t i n d i c a t o r s t r a i n . B a c t e r i a were k i l l e d by i n v e r t i n g the p l a t e s over chloroform soaked f i l t e r paper f o r 20 min. The c o l o n i e s were scraped o f f the agar surface using s t e r i l e g l a s s microscope s l i d e s . Another 20 min - chloroform treatment was used to k i l l any remaining b a c t e r i a . Residual chloroform vapours were removed by exposing the p l a t e s i n a laminar a i r flow clean bench f o r 20 min. Suspensions of i n d i c a t o r s t r a i n s (AG60 * 0.1 or about 4 x 10 CFU/ml) were prepared i n s t e r i l e d i s t i l l e d water (SDW). A 0.1 u l a l i q u o t was added to 10 ml of molten peptone s o f t agar (con t a i n i n g 1% bacto-peptone and 0.6% agar) held at 50°C. The suspensions were mixed on a vortex mixer f o r about 20 s and poured over the surface of the t e s t agar p l a t e s . These p l a t e s were then incubated at 26°C and observed a f t e r 24 h to 48 h. Zones of i n h i b i t i o n were rated from s l i g h t to c l e a r on an a r b i t r a r y s c a l e of 0 to 5. This procedure f o r preparation of the i n d i c a t o r lawns was followed i n subsequent experiments unless otherwise noted. B a c t e r i o c i n a c t i v i t y was detected i n broth c u l t u r e s by the spot assay t e s t (Mayr-Harting et a l . 1972) f o r s t r a i n s 379, 373, 440 and 626. Test s t r a i n s were grown i n d u p l i c a t e i n 20 ml of n u t r i e n t broth i n 50 ml Erlenmeyer f l a s k s at 26°C f o r 48 h i n a shaking water bath. B a c t e r i a l c e l l s were removed by c e n t r i f u g a t i o n (head 874 - 10 000 x f o r 20 min.) at 4°C i n an IEC Centrifuge Model 20-8 (from now on c a l l e d low-speed c e n t r i f u g a t i o n ) . The supernatants were f i l t e r - s t e r i l i z e d and t h r e e - f o l d d i l u t i o n s e r i e s were prepared i n SDW. A 10 y l drop of each d i l u t i o n i n the s e r i e s was placed i n d u p l i c a t e onto i n d i c a t o r lawns. I n h i b i t i o n zones were observed a f t e r 24-48 h. Induction experiments were done using a standard UV l i g h t source (General E l e c t r i c Germicidal Tube G30T8). S t r a i n s 379, 373, 440, 625 and 626 were tested i n in d u c t i o n experiments. A l i q u o t s (0.1 ml) of b a c t e r i a l c e l l suspensions (Aggo 53 0.1) of each s t r a i n were in o c u l a t e d i n t o 30 ml n u t r i e n t broth i n 50 ml Erlenmeyer f l a s k s . The f l a s k s were incubated on a shaking water bath f o r 8 h (mid-exponential growth phase). Each 30 ml was equally d i v i d e d i n t o two p e t r i dishes and placed 26 cm below the u n f i l t e r e d UV l i g h t f o r 20 sec. The exposed c u l t u r e s were placed back i n t o the f l a s k s and incubated another 4 h on the shaking water bath. The suspensions received a low-speed c e n t r i f u g a t i o n and the supernatants were f i l t e r s t e r i l i z e d . D i l u t i o n s e r i e s were prepared and 10 y l a l i q u o t s were spot assayed. The experiments were d u p l i c a t e d and repeated twice. The p l a t e s were incubated at 26°C f o r 48 h before observation f o r i n h i b i t i o n zones which were recorded as p o s i t i v e , weak or no i n h i b i t i o n . C. P a r t i a l P u r i f i c a t i o n To determine the optimal concentration of Mitomycin C (Sigma Chemical Co. St. L o u i s , U.S.A.) required f o r i n d u c t i o n , s o l u t i o n s at the f i n a l concentrations of 0.2, 0.4, 0.6, 0.8 and 1.0 yg/ml were prepared i n SDW. Each concentration was added at the mid-exponential growth phase to n u t r i e n t broth c u l t u r e s of s t r a i n s 379, 373, 440 and 626 incubated i n a shaking water bath. Further incubation was done f o r another 6 hours. The preparations received low-speed c e n t r i f u g a t i o n and the supernatants were f i l t e r s t e r i l i z e d . Three-fold d i l u t i o n s e r i e s i n SDW were prepared and spot assayed onto the i n d i c a t o r lawns prepared as pr e v i o u s l y noted. I n h i b i t i o n zones were observed a f t e r 48 h incubation and an a r b i t r a r y r a t i n g from 0 to 5 was recorded. The ba c t e r i o c i n - p r o d u c i n g s t r a i n s were c u l t u r e d i n 1 L of n u t r i e n t broth. S t a r t i n g inoculum c o n s i s t e d of 1 ml of b a c t e r i a l suspension (Aggo B 1) prepared i n SDW. These c u l t u r e s were incubated f o r 8 h (to mid-exponential growth phase) on a shaker at 26°C. Mitomycin C was added to a f i n a l concentration of OA yg/ml. A f u r t h e r incubation of 6 h was allowed before harvest. B a c t e r i a l c e l l s were removed by low speed c e n t r i f u g a t i o n . An equal volume of saturated (NHi+)2S0i t s o l u t i o n was added drop-wise with s t i r r i n g . The mixture was adjusted to pH 7.0 and allowed to stand overnight at 4°C. The r e s u l t i n g p r e c i p i t a t e s were c o l l e c t e d by low speed c e n t r i f u g a t i o n and r e d i s s o l v e d i n 10 ml 0.01 M phosphate b u f f e r (PBS) pH 7.2 co n t a i n i n g 0.85% NaCl. These s o l u t i o n s were d i a l y s e d overnight at 4°C against PBS. The d i a l y s a t e s were c e n t r i f u g e d i n a Beckman LS-40, type 65 f i x e d angle r o t o r at 100 000 x £ and 120 000 x £ f o r 60 min, and at 150 000 x £ f o r 90 min. The p e l l e t s recovered were resuspended i n 5 ml 0.01M PBS. An a d d i t i o n a l low speed c e n t r i f u g a t i o n removed i n s o l u b l e m a t e r i a l . The p u r i f i c a t i o n procedure i s summarized i n Figure 1. Both p e l l e t f r a c t i o n s and supernatants were test e d f o r b a c t e r i o c i n a c t i v i t y against the s e n s i t i v e i n d i c a t o r s t r a i n s by the spot assay technique as described above. Supernatant f r a c t i o n s were run on a Sephadex G-200 column (5.5 cm high and 1.5 cm diameter) p r e v i o u s l y e q u i l i b r a t e d with 25 ml PBS. Samples (2.5 ml) were allowed to run i n and PBS added. Void volumes (3.5 ml) and included volumes (8.5 ml) were c o l l e c t e d i n PBS b u f f e r . Three-fold d i l u t i o n s e r i e s were prepared from the void volumes and the included volumes. A l i q u o t s (10 y l ) were spot assayed f o r b a c t e r i o c i n a c t i v i t y as pr e v i o u s l y described. A c t i v i t y was recorded as the l a s t d i l u t i o n at which i n h i b i t o r y a c t i v i t y was detected on the i n d i c a t o r lawn. The high speed supernatants were al s o f r a c t i o n a t e d on a Sephacryl S-300 column (33 cm high and 2.5 cm diameter). The column was Mitomycin C induced broth c u l t u r e s c e n t r i f u g a t i o n (10,000 g f o r 20 min) P e l l e t d i s c a r d C e l l f r e e cu ture f i l r a t e (NHi +)2S0i t p r e c i p i t a t i o n c e n t r i f u g a t i o n (10,000 g f o r 20 min) Supernatant ( S ^ P e l l e t ( P i ) i A d i a l y s i s (PBS: contained 0.01M K 2HP0 4-KH 2P0 l t b u f f e r at pH 7.2 + 0.85% NaCl) c e n t r i f u g a t i o n (10,000 g f o r 20 min) Supernatant ( S 2) P e l l e t ( P 2 ) - d i s c a r d -I c e n t r i f u g a t i o n (90 min at 150 000 g) Supernatant ( S 3 ) P e l l e t ( P 3 ) (resuspended i n 3 ml PBS) Gel f i l t r a t i o n (Sephadex G-200) Retained Excluded Figure 1. Flow chart f o r p a r t i a l p u r i f i c a t i o n of b a c t e r i o c i n from Erwinia carotovora. e q u i l i b r a t e d with PBS p r i o r to use. Samples of the high speed supernatant (2 ml a l i q u o t s ) were run i n and 50, 2.5 ml f r a c t i o n s were c o l l e c t e d at a flow r a t e of 2.5 ml/min. U l t r a v i o l e t absorption was monitored sp e c t r o p h o t o m e t r i c a l l y at 253 nm with a UV-monitor. Each f r a c t i o n was test e d f o r b a c t e r i o l y t i c a c t i v i t y against i n d i c a t o r s t r a i n 504 by the spot assay technique. The type and r a t i n g or diameter of the i n h i b i t i o n zones were recorded. A standard curve was also determined on the same column using proteins of known molecular weight, c a t a l a s e (MW 2.5 x 1 0 5 ) , a p o f e r r i t i n (MW 4.8 x 1 0 5 ) , cytochrome C (MW 1.22 x 10 4) and phosphorylase B (MW 9.2 x 10 ). These p r o t e i n s were run i n at the concentration of 2.5 mg/ml. C h a r a c t e r i s t i c s of the p a r t i a l l y p u r i f i e d b a c t e r i o c i n preparations were al s o s t u d i e d . S e n s i t i v i t y to t r y p s i n (Sigma Chemical Co. St. Louis U.S.A. Type I I , crude t r y p s i n from porcine pancreas) was tested using the method of Itoh ^ t a l . (1978). However, the sample s i z e used i n the present work was 100 y l p a r t i a l l y p u r i f i e d b a c t e r i o c i n preparations (the resuspended p e l l e t s and supernatant f r a c t i o n s ) from u l t r a c e n t r i f u g a t i o n . S t a b i l i t y to heat (50°C and 80°C f o r 10 min ) was determined with 1 ml a l i q u o t s i n t h i n - w a l l glass t e s t tubes with constant shaking. The r e s i d u a l b a c t e r i o c i n a c t i v i t y ( a f t e r treatment with t r y p s i n or heat) was te s t e d by the spot assay technique using a l l the re p r e s e n t a t i v e i n d i c a t o r s t r a i n s . The presence or absence of i n h i b i t o r y zones was recorded. D. E l e c t r o n microscopy The resuspended high-speed p e l l e t s and supernatants were dropped onto copper g r i d s coated with c o l l o d i o n - c a r b o n . The g r i d s were st a i n e d with 2% phosphotungstic acid (20 drops) pH 7.1. Preparations were observed i n a P h i l l i p s EM 300 e l e c t r o n microscope and photographed. E. Dual C u l t u r e Studies C u l t u r e c o n d i t i o n s f o r these studies were maintained as p r e v i o u s l y noted. S t r a i n s 379, 373, 440 and 626 were used as r e p r e s e n t a t i v e s t r a i n s of Ecc from serogroup XI and s t r a i n s SR8 ( I ) , 504 ( X V I I I ) , 530 (XX) and 496 (XXII) from the s e n s i t i v e serogroups. B a c t e r i a l suspensions (A660 K D were prepared i n SDW as a s t a r t i n g concentration and a t e n - f o l d d i l u t i o n s e r i e s (corresponding to A 6 6 0 » 1, 0.1, 0.01, 0.001, 0.0001 and 0.00001) were prepared. The concentration of the s e n s i t i v e s t r a i n s was kept constant at Aggo ra 0.01 (3 x 10 5 CFU/ml). While the f u l l concentration range of the producer c e l l s was employed, the s t a r t i n g r a t i o s of the producers to s e n s i t i v e c e l l s were designated as 100:1, 10:1, 1:1, 1:10, 1:100 and 1:1000. The c o n t r o l s consisted of the same s t a r t i n g r a t i o of a non-producer to s e n s i t i v e c e l l s as w e l l as s e n s i t i v e c e l l s alone. The dual c u l t u r e s were v i g o r o u s l y mixed f o r about 20 s on a vortex mixer. A l i q u o t s of 0.1 ml from the mixed c u l t u r e s were in o c u l a t e d i n t o 20 ml of n u t r i e n t broth i n 50 ml Erlenmeyer f l a s k s . They were incubated i n a shaking water bath. A f t e r 48 h s e r i a l d i l u t i o n s were prepared and plated i n d u p l i c a t e onto a-MG-TZC s e l e c t i v e medium ( P h i l l i p s and Kelman 1982). The pl a t e s were incubated f o r 72 h at 26°C. A f t e r incubation the number of red c o l o n i e s (Eca) and the number of opaque c o l o n i e s (Ecc) were recorded. In some experiments mixed c u l t u r e s at the i d e n t i c a l s t a r t i n g r a t i o s were simultaneously i n o c u l a t e d onto potato tuber d i s c s . The d i s c s were prepared from potato tubers which were s u r f a c e - d i s i n f e s t e d by immersion f o r 10 min i n 10% Chlorox ( f i n a l concentration of NaOCl 0.5%). A s t e r i l e cork borer (4mm diam.) was used to cut 3 mm-thick potato d i s c s . The d i s c s were placed i n t o the w e l l s of s t e r i l i z e d spot p l a t e s and each treatment r e p l i c a t e d four times. Each d i s c received 0.1 ml of a mixed c u l t u r e suspension. Ten f o l d s e r i a l d i l u t i o n s of the r o t t e d t i s s u e s were prepared i n SDW and in o c u l a t e d to d u p l i c a t e p l a t e s of a-MG-TZC medium. Colony counts were made as noted above. RESULTS A. Screening and Detection B a c t e r i o c i n production and s e n s i t i v i t y i n E. carotovora as demonstrated by the agar overlay technique v a r i e d among s t r a i n s i n the eleven serogroups tested (Table 1 ). The one or two s t r a i n s tested i n each of seven biochemically E_. carotovora subsp. carotovora (Ecc) serogroups ( I I I , IV, V, IX, XI, XVI and XXI), were b a c t e r i o c i n producers. The one or two s t r a i n s t e s t e d i n each of seven serogroups ( I , I I I , IV, V, XVII I , XX and XXII) were b a c t e r i o c i n s e n s i t i v e . Three serogroups ( I I I , IV and V) contained s t r a i n s that were both b a c t e r i o c i n producers and b a c t e r i o c i n i n d i c a t o r s . A l l E. carotovora subsp. a t r o s e p t i c a (Eca) serogroups ( I , X V I I I , XX and XXII) were found to be non-producers and b a c t e r i o c i n s e n s i t i v e against s t r a i n s employed i n t h i s study. Representative s t r a i n s i n four serogroups (IX, XI, XVI and XXI) were not s e n s i t i v e to b a c t e r i o c i n s produced by any of the eleven serogroups t e s t e d . S e n s i t i v i t y to some producer s t r a i n s v a r i e d between s t r a i n s i n the same serogroup when more than one s e n s i t i v e s t r a i n was t e s t e d . With the exception of serogroup X V I I I , s t r a i n s i n serogroups s e n s i t i v e to one producer were also s e n s i t i v e to at l e a s t a second producer serogroup. Serogroups I I I and V showed s e n s i t i v i t y to s i x and four producer serogroups r e s p e c t i v e l y . At l e a s t one s t r a i n i n a l l Eca serogroups was s e n s i t i v e to the re p r e s e n t a t i v e producing s t r a i n s i n serogroup XI (E c c ) . Only some Eca serogroups were s e n s i t i v e to the remaining producer serogroups (V, IX and XXI). B a c t e r i o c i n production as detected by the agar overlay technique with s e n s i t i v e s t r a i n s i n four serogroups (Eca) was not an absolute Table 1. S e n s i t i v i t y to and production of b a c t e r i o c i n s by s t r a i n s of the predominant potato serogoups of Erwinia carotovora i n B r i t i s h Columbia B a c t e r i o c i n s e n s i t i v i t y of s t r a i n s i n serogroups B a c t e r i o c i n I I I I IV V IX XI XVI XVIII XX XXI XXII producing — — Serogroup s t r a i n SR8 82 95 14 90 94 84 270 385 315 17 368 530 295 555 I SR8,82 a _ - - - - -I I I 95 _ + + - - - - - -IV 14 - - + - + + - - - _ - -V 90,94 + + + - - - - - - - - - + + IX 84 + - ± - - - - - - - - + XI 270,385 + + ± - - - - - - - + - + + XVI 315 ± - + + - - - _ - -XVIII 17 - - - - - - - _ - -XX 368,530 _ - - - - - - _ - -XXI 295 - + + + + + - - - - - + XXII 555 - - - - - - - - - - -a No i n h i b i t i o n i n a l l r e p l i c a t e s , ± weak + i n h i b i t i o n i n at l e a s t two r e p l i c a t e s . i n h i b i t i o n i n at l e a s t one r e p l i c a t e , Results of two r e p l i c a t e s i n each of two experiments. serogroup c h a r a c t e r i s t i c (Table 2 ) . Representative s t r a i n s from a l l four serogroups were s e n s i t i v e to 31/44 of the bac t e r i o c i n - p r o d u c i n g s t r a i n s i n serogroup XI. These s t r a i n s were designated as " t y p i c a l producers". S e n s i t i v i t y of s t r a i n s w i t h i n and among the four s e n s i t i v e serogroups v a r i e d against 10 serogroup XI s t r a i n s r e f e r r e d to as " d i f f e r e n t i a l producers". None of the i n d i c a t o r s t r a i n s was s e n s i t i v e to three s t r a i n s c l a s s i f i e d as "non-producers". S t r a i n s i n serogroup XVIII which were biochemically Ecc showed s i m i l a r s e n s i t i v i t y patterns to s t r a i n s that were biochemically Eca. Both Mitomycin C and UV l i g h t induced b a c t e r i o c i n production i n n u t r i e n t broth c u l t u r e s tested by the spot assay (Table 3 ) . Noninduced broth c u l t u r e s of s t r a i n 440 and the "non-producers" showed no b a c t e r i o c i n a c t i v i t y against any of the four s e n s i t i v e s t r a i n s . However a f t e r i n d u c t i o n , a c t i v i t y was detected i n broth c u l t u r e s of s t r a i n 440 by a l l the s e n s i t i v e s t r a i n s . Both non-producers showed b a c t e r i o c i n a c t i v i t y a f t e r i n d u c t i o n by Mitomycin C but not UV l i g h t . Only s t r a i n s i n serogroups XVIII and XXII showed s e n s i t i v i t y to b a c t e r i o c i n induced i n the "non-producers". Enhanced b a c t e r i o c i n production by the " t y p i c a l producer" s t r a i n 379 and " d i f f e r e n t i a l producer" s t r a i n 373 a f t e r i n d u c t i o n by both Mitomycin C and UV l i g h t was observed as greater c l e a r i n g of the i n h i b i t i o n zones. The degree of c l e a r i n g observed i n the agar overlay technique v a r i e d among s e n s i t i v e serogroups and with the s t r a i n s used i n any one serogroup (Table 4 ) . " T y p i c a l producer" s t r a i n s showed maximum a c t i v i t y (a r a t i n g of 5) against s t r a i n s i n serogroup I , intermediate a c t i v i t y against most s t r a i n s i n serogroup XVIII and high a c t i v i t y (a r a t i n g Table 2. S e n s i t i v i t y of selected s t r a i n s of four Erwlnia carotovora subsp. atroseptica serogroups to b a c t e r i o c i n s produced by s t r a i n s of Erwinia carotovora subsp. carotovora serogroups XI i s o l a t e d from potato i n B r i t i s h Columbia Reaction of sen s i t i v e s t r a i n s i n serogroups Producer I XVIII XX XXII s t r a i n s i n serogroup XI * * * og c - i ^ o m < j o o ^ H f n o o C T » c s i m o ^ H i n r ^ i n v D O f - t c s m ^ D r ^ o c N v o "Typical producers" *1 *4 350 360 + 3 + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + 361 37* 377 379-38* 386-390 393-*00 *02 *05 608 270 + + + + + + + + + + + + + + + - - + + + + + + + + + + + + + + + + + + " D i f f e r e n t i a l producers" 20 - - - - - - - - + + - + + + - . - - - - - - - -27 + + + + + + + + - - - + - + - + - - - - + + + + + + + + + + + + + + + 282 - - - - - - - + - - - - . _ - . - - - - - - - - - - + + + + + + + + + 362 - - - - - - + - - - + - - - - - - - - - - - - - -371 - - - - - - - - . - - - - + + + - - - - - - - - - - . 373 + + + + + + + ± - - - ± ± ± - - - . - _ + + + + + + . 376 + + + + + + + + + + + + + + + + - - - - + + + + - + -385 + + + + + + + + + + + + + + + + - - - - + + + + - + + 401 + . - - + + + - - - - - + + - . - + -**0 + + + + + + + - - - - - - - - - _ _ _ _ ± + ± + + - -+ - + + + + + + ± + + + + + + + + + + - + - + + + + + - + "Non-producers" 351 625 626 a+ i n h i b i t i o n i n at least two r e p l i c a t e s , ± weak i n h i b i t i o n i n at least one r e p l i c a t e , - no i n h i b i t i o n i n a l l r e p l i c a t e s . Results of two r e p l i c a t e s i n each of two experiments. •Indicates E. carotovora subsp. caratovora s t r a i n s . Table 3. Bacteriocin a c t i v i t y of s t r a i n s of Erwinla carotovora subsp. carotovora serogroup XI when induced with UV l i g h t and Mitomycin C as detected i n the spot assay technique by s e n s i t i v e s t r a i n s corresponding to four serogroups of Erwinla carotovora subsp. atroseptica Bacteriocin production detected by s e n s i t i v e s t r a i n s i n serogroups St r a i n s i n I XVIII XX XXII serogroup XI SR8 504 530 496 Non- UV Mitomycin Non- UV Mitomycin Non- UV Mitomycin Non- UV Mitomycin induced l i g h t C Induced l i g h t C Induced l i g h t C Induced l i g h t C Typical producer 379 + + + + + + + + + + + + i no D i f f e r e n t i a l producers 373 ± + + ± + + ± + + + + + 362 - + + - + + - + + - + + 440 - + + - + + - + + - + . + Non-producers 625 . . . . . + . _ _ . . + 626 . _ . . _ + . _ . . _ + a+ i n h i b i t i o n i n at leas t two r e p l i c a t e s , ± weak i n h i b i t i o n i n at leas t one r e p l i c a t e , - no I n h i b i t i o n i n a l l r e p l i c a t e s . Results of two r e p l i c a t e s i n each of two experiments. Table 4. Degree of i n h i b i t i o n of selected s t r a i n s of Erwinia carotovora subsp. a t r o s e p t i c a by b a c t e r i o c i n - producing s t r a i n s of Erwinia carotovora subsp. carotovora serogroup XI Degree of i n h i b i t i o n by b a c t e r i o c i n s e n s i t i v e s t r a i n s i n serogroups S t r a i n s i n I XVIII XX XXII serogroup XI SR8 193 142 18 504 620 530 531 495 496 T y p i c a l producers 379 5 a 5 5 3.5 3.5 4 5 5 3.5 4 380 5 5 5 2.5 2 2 5 4 4 4 385 5 5 5 3.5 2.5 2.5 5 4 4 4 394 5 5 5 2.5 2.5 3 4.5 4 3 4 D i f f e r e n t i a l producers 20 0 0 0 3 5 2 0 0 0 0 282 0 0 0 0 0 0 1 0 1 0 373 5 5 5 0.5 0.5 1 5 5 3 4 440 5 5 5 0 0 0 5 5 3.5 4 Non-producers 625 0 0 0 0 0 0 0 0 0 0 626 0 0 0 0 0 0 0 0 0 0 Numbers i n d i c a t e degree of i n h i b i t i o n from s l i g h t (1) to complete (5) i n the agar overlay technique. Mean r a t i n g of two r e p l i c a t e s i n each of three experiments. of 4) against serogroup XX and XXII. " D i f f e r e n t i a l producer" s t r a i n s 20 and 282 showed poor or no a c t i v i t y against the r e p r e s e n t a t i v e s e n s i t i v e s t r a i n s i n most of the serogroups. S t r a i n s 373 and 440 showed good a c t i v i t y against s t r a i n s i n serogroups I , XX and XXII but weak or no a c t i v i t y against s t r a i n s i n serogroup XV I I I . These data suggested that the threshold quantity required by the s e n s i t i v e s t r a i n s to show b a c t e r i o c i n s e n s i t i v i t y v a r i e d . The r e c i p r o c a l of the d i l u t i o n end-point from broth c u l t u r e s c o n t a i n i n g b a c t e r i o c i n a c t i v i t y confirmed t h i s observation (Table 5 ) . S t r a i n s i n serogroups XVIII and XXII were more s e n s i t i v e than s t r a i n s i n other serogroups tested to b a c t e r i o c i n i n noninduced broth c u l t u r e s of 379. Other s t r a i n s were e i t h e r not s e n s i t i v e or only weakly s e n s i t i v e . In general three to twenty-seven f o l d increases i n b a c t e r i o c i n production were induced with Mitomycin C. S e n s i t i v i t y of the four i n d i c a t o r s t r a i n s was ge n e r a l l y highest i n b a c t e r i o c i n preparations of s t r a i n 379 followed by 373, 440 and 626. Considering both induced and non-induced c u l t u r e s of Ecc s t r a i n s , s t r a i n 496 was the most s e n s i t i v e i n d i c a t o r s t r a i n . The f i n a l concentration of Mitomycin C that induced maximum b a c t e r i o c i n production v a r i e d from 0.2 - 0.8 pg/ml depending upon the combination of both the producer and i n d i c a t o r s t r a i n s (Table 6 ) . The optimum f i n a l concentration of Mitomycin C was defined as the minimum f i n a l concentration of Mitomycin C that induced maximum b a c t e r i o c i n production. These optimum values v a r i e d depending upon the combination of both the producer and i n d i c a t o r s t r a i n s . V a r i a b i l i t y i n the optimum values occurred due to d i f f e r e n t i a l s e n s i t i v i t y of the i n d i c a t o r s t r a i n s to the b a c t e r i o c i n being produced. Detectable b a c t e r i o c i n a c t i v i t y was Table 5. R e c i p r o c a l d i l u t i o n end-point at which a c t i v i t y could be detected by the spot assay technique In broth c u l t u r e f i l t r a t e s of non-induced and induced producer s t r a i n s of E r w i n i a carotovora subsp. carotovora serogroup XI Log3 r e c i p r o c a l d i l u t i o n end-point of the b a c t e r i o l y t i c a c t i v i t y against s e n s i t i v e s t r a i n s i n serogroups S t r a i n s i n serogroup XI SR8 XVIII XX XXII 504 530 496 T y p i c a l producers 379 Non-Induced Induced 4 2 4 1 4 2 5 D i f f e r e n t i a l producers 373 Non-induced 0 0 0 2 Induced 1 4 2 4 D i f f e r e n t i a l producer 440 Non-Induced - -Induced 1 1 2 2 Non-producer 626 Non-induced - - - -Induced 0 2 - 2 Each value Is the mean of two r e p l i c a t e s i n each of two experiments. - tes t e d but no a c t i v i t y detected. Table 6. R e c i p r o c a l d i l u t i o n end-point at which a c t i v i t y could be detected by the spot assay technique i n broth c u l t u r e f i l t r a t e s of non-induced and induced producer s t r a i n s of Erwinia  carotovora subsp. carotovora serogroup XI when induced with d i f f e r e n t concentrations of Mitomycin C Log3 of r e c i p r o c a l d i l u t i o n end-point of the S t r a i n s b a c t e r i o l y t i c a c t i v i t y against s e n s i t i v e s t r a i n s with Mitomycin C (yg/ml) Producer S e n s i t i v e '. 0 0.2 0.4 0.6 0.8 1.0 T y p i c a l 379 SR8 (I) 1 a 3 4 4 4 4 504 (XVIII) 2 4 4 5 5 5 530 (XX) 1 3 4 4 5 5 496 (XXII) 2 3 5 6 6 6 f f e r e n t i a l 373 SR8 (I) 0 1 1 1 2 2 504 (XVIII) 0 3 4 4 4 4 530 (XX) 0 2 2 4 5 5 496 (XXII) 2 4 4 4 4 4 440 SR8 (I) b 1 1 1 1 1 504 (XVIII) - 1 1 1 1 1 530 (XX) - 2 2 4 5 5 496 (XXII) - 2 2 5 5 5 >n-producer 626 SR8 (I) _ _ 0 0 0 504 (XVIII) - - 2 2 2 2 530 (XX) - - - - - -496 (XXII) - - 2 2 2 2 Each value i s the mean of two r e p l i c a t e s i n each of two experiments. - t e s t e d but no a c t i v i t y was detected. apparent even at the lowest f i n a l concentration of Mitomycin C tes t e d (0.2 ug/ml) except f o r non-producer s t r a i n 626 where a higher f i n a l c o n centration (0.4 yg/ml) was r e q u i r e d . In a few cases the lowest f i n a l c o ncentration of Mitomycin C seemed to be a l l that was needed to induce maximum b a c t e r i o c i n a c t i v i t y . B. P a r t i a l P u r i f i c a t i o n P a r t i a l p u r i f i c a t i o n g r e a t l y enhanced b a c t e r i o c i n a c t i v i t y i n the " t y p i c a l " and " d i f f e r e n t i a l producers" as detected by the spot assay t e s t (Table 7 ) . A f t e r (NHu^SOk p r e c i p i t a t i o n and u l t r a c e n t r i f u g a t i o n the r e c i p r o c a l s of the d i l u t i o n end-points f o r the resuspended p e l l e t s were higher than those from the supernatants. S t r a i n s i n serogroups X V I I I , XX and XXII were g e n e r a l l y more s e n s i t i v e to the resuspended p e l l e t f r a c t i o n s of the " t y p i c a l producer" s t r a i n 379 and " d i f f e r e n t i a l producer" s t r a i n 440 but t h i s pattern of s e n s i t i v i t y was not c l e a r against b a c t e r i o c i n producing s t r a i n 373. Only s t r a i n s i n serogroups XVIII and XXII showed s e n s i t i v i t y to the p a r t i a l l y p u r i f i e d b a c t e r i o c i n of the "non-producer" s t r a i n 626. When the supernatants were f r a c t i o n a t e d on Sephadex G-200, a c t i v i t y was detected both i n the void volumes and i n the f r a c t i o n s r e t a i n e d by the columns (the included volume). The same pattern of d i f f e r e n t i a l s e n s i t i v i t y noted above was apparent i n both of these f r a c t i o n s . S t r a i n SR8 (serogroup I) was not s e n s i t i v e to the f r a c t i o n s r etained on the column. Only s t r a i n 504 and 496 showed d i f f e r e n t i a l s e n s i t i v i t y to the "non-producer" s t r a i n 626. Both c l e a r and d i f f u s e i n h i b i t i o n zones were detected i n the spot assay t e s t s from the various f r a c t i o n s (Figure 2 ) . The resuspended p e l l e t s always showed c l e a r zones of i n h i b i t i o n of uniform diameter Table 7. R e c i p r o c a l d i l u t i o n end-point at which a c t i v i t y could be detected by the spot assay technique i n d i f f e r e n t f r a c t i o n s of p a r t i a l l y p u r i f i e d b a c t e r i o c i n preparations S t r a i n s and F r a c t i o n s Log3 of r e c i p r o c a l d i l u t i o n end-point of the b a c t e r i d y t i c a c t i v i t y against s t r a i n s i n serogroups SR8 XVIII 504 XX 530 XXII 496 T y p i c a l producer 379 pf S 3 G200 ex. S 3 G200 r e t d , D i f f e r e n t i a l producer 373 P 3 S 3 S 3 G200 ex. S 3 G200 r e t . 440 P 3 S 3 S 3 G200 ex. S 3 G200 r e t . Non-Producer 626 P 3 S 3 S 3 G200 ex. S 3 G200 r e t . 10* 3 2 9 3 0 3 2 0 14 7 4 3 7 3 3 2 4 4 2 2 2 4 0 15 6 4 1 9 3 0 2 4 3 0 2 15 5 5 4 9 3 0 2 6 4 0 2 2 4 3 2 In d i c a t e s p e l l e t (3) resuspended i n PBS from high speed c e n t r i f u g a t i o n . Refers to supernatant (3) a f t e r high speed c e n t r i f u g a t i o n . Refers to void volume (3.5 ml) c o l l e c t e d when 2.5 ml of S 3 was run through Sephadex G-200. Refers to included volume (8.5 ml) eluted from Sephadex G-200 column. Each value i s the means of two r e p l i c a t e s i n each of two experiments. f - t e s t e d but no a c t i v i t y detected. Figure 2 . B a c t e r i o c i n a c t i v i t y against i n d i c a t o r s t r a i n s of Erwinia carotovora subsp. a t r o s e p t i c a i n t h r e e - f o l d d i l u t i o n s e r i e s (counter-clockwise) from Mitomycin C induced c u l t u r e f i l t r a t e s of Erwinia carotovora subsp. carotovora s t r a i n s at d i f f e r e n t stages i n p u r i f i c a t i o n . _A. Clear i n h i b i t i o n zones detected i n the resuspended p e l l e t f r a c t i o n f o l l o w i n g (NHi+JSO^ p r e c i p i t a t i o n and u l t r a c e n t r i f u g a t i o n f o r 90 min. at 150 000 x q. B. D i f f u s e i n h i b i t i o n zones surrounding c l e a r zones detected i n the supernatant f r a c t i o n f o l l o w i n g (NH l t ) 2 S 0 i + p r e c i p i t a t i o n and u l t r a c e n t r i f u g a t i o n f o r 90 min. at 150 000 x _g_. C_. D i f f u s e i n h i b i t i o n zones surrounding c l e a r zones detected i n the void volume when the supernatant f r a c t i o n s were run on Sephadex G-200 column. D_. D i f f u s e i n h i b i t i o n zones detected i n the included volume when supernatant f r a c t i o n s were run on a Sephadex G-200 column. r e g a r d l e s s of d i l u t i o n (Figure 2A). This was c h a r a c t e r i s t i c of p a r t i a l l y p u r i f i e d b a c t e r i o c i n preparations against the s e n s i t i v e s t r a i n s i n a l l serogroups. Clear i n h i b i t i o n zones were also found with a l l s e n s i t i v e s t r a i n s against the "high-speed" supernatants. But s t r a i n s 504, 530 and 496 i n a d d i t i o n had l a r g e r d i f f u s e i n h i b i t i o n zones surrounding the c l e a r zones (Figure 2B). The diameters of the c l e a r zones remained constant u n t i l l o s t by d i l u t i o n . The diameter of the d i f f u s e zones decreased with d i l u t i o n and were l o s t at lower d i l u t i o n s than the c l e a r zones. The "high-speed" supernatant f r a c t i o n s d i d not show b a c t e r i o l y t i c a c t i v i t y against the producing s t r a i n s . Mitomycin C c o n t r o l (at the f i n a l c oncentration of 0.4 mg/ml) gave only small (2mm) and weak i n h i b i t i o n zones. These r e s u l t s suggested that two b a c t e r i o c i n s were present at d i f f e r e n t concentrations or that the s e n s i t i v i t y of the i n d i c a t o r s t r a i n s to the two types of b a c t e r i o c i n s v a r i e d . When the p a r t i a l l y - p u r i f i e d supernatants from the t y p i c a l and d i f f e r e n t i a l producers were f r a c t i o n a t e d on Sephadex G-200, both c l e a r and d i f f u s e zones were associated with the void volumes (Figure 2C). A l l the i n d i c a t o r s t r a i n s showed a s i m i l a r s e n s i t i v i t y . In contrast only d i f f u s e zones were associated with the ret a i n e d f r a c t i o n s (Figure 2D) detected by s t r a i n s 504, 530 and 496. Further separation of the high speed supernatant on Sephacryl S-300 showed a c t i v i t y against s t r a i n 504 (serogroup XVIII) i n two s e r i e s of f r a c t i o n s (Figure 3 ) . F r a c t i o n s 17-24 showed only c l e a r i n h i b i t i o n zones whereas f r a c t i o n s 33-46 showed only d i f f u s e zones. S e r i a l d i l u t i o n s of f r a c t i o n s 33-46 r e s u l t e d i n an a c t i v i t y spectrum suggesting 5 10 15 20 25 30 35 40 45 FRACTION NO. Figure 3. B a c t e r i o c i n a c t i v i t y (detected by i n d i c a t o r s t r a i n 504) i n the p a r t i a l l y p u r i f i e d "high speed" supernatant ( s t r a i n 379) a f t e r f r a c t i o n a t i o n on a Sephacryl S-300 column. a maximum of two peaks with only weak evidence f o r the second peak (Figure 4 ) . The estimated molecular weights c a l c u l a t e d from the peaks of the i n h i b i t o r y a c t i v i t y i n f r a c t i o n s 17-24 was about 224 500 D, i n f r a c t i o n s 33-39 was about 29 500 D and i n f r a c t i o n s 40-46 was about 17 500 D (Figure 5 ) . Resuspended high speed p e l l e t preparations when v i s u a l i z e d under the e l e c t r o n microscope contained bacteriophage t a i l - l i k e p a r t i c l e s (Figure 6A and 6B). The dimensions of the p a r t i c l e s were about 139 x 20 nm. Most p a r t i c l e s from s t r a i n 379 preparations showed contracted sheaths s i t u a t e d at various p o s i t i o n along the inner cores. Some p a r t i c l e s were v i s u a l i z e d as empty sheaths without the inner cores, others j u s t as the inner cores without the sheaths. The empty sheaths were more fr e q u e n t l y observed i n preparations from s t r a i n 440. However, no bacteriophage t a i l - l i k e p a r t i c l e s or components were observed i n the supernatant f r a c t i o n s . A l l four f r a c t i o n s which showed b a c t e r i o c i n a c t i v i t y or " b a c t e r i o c i n - l i k e " a c t i v i t y were heat l a b i l e when subjected to 80°C f o r 10 min. However, the four b a c t e r i o l y t i c f r a c t i o n s were not s e n s i t i v e to t r y p s i n . C. Antagonism i n Dual C u l t u r e s In v i t r o antagonism was demonstrated i n dual broth c u l t u r e s of the producer and s e n s i t i v e s t r a i n s (Table 8 ) . The growth of s e n s i t i v e s t r a i n s i n serogroups X V I I I , XX and XXII was not detected even at the s t a r t i n g r a t i o of approximately one t y p i c a l producer c e l l to 1000 s e n s i t i v e c e l l s . Growth of s t r a i n SR8 (serogroup I) was prevented at the s t a r t i n g r a t i o of one producer to 10 s e n s i t i v e c e l l s . The a c t i v i t y 243 Z 81-| 6 a. Q Z 2 7 H 3J 35 40 FRACTION NO. 45 Figure 4. R e l a t i v e b a c t e r i o l y t i c a c t i v i t y (detected by i n d i c a t o r s t r a i n 504) i n f r a c t i o n s 33 to 46 obtained when the p a r t i a l l y p u r i f i e d high speed supernatant from producer s t r a i n 379 was run on a Sephacryl S-300 column. I APOFERRITIN T 1 r 4 5 5.0 5.5 LOG MOLECULAR WEIGHT Figure 5. Standard curve of Kav Vs lo g molecular weight p l o t t e d using p r o t e i n of known molecular weights ( a p o f e r r i t i n , c a t a l a s e , phosphorylase B and cytochrome C) determined from g e l f i l t r a t i o n (Sephacryl S-300). (A) i n d i c a t e s Kav Vs log molecular weight of the b a c t e r i o c i n - l i k e component at f r a c t i o n #19, at f r a c t i o n #37 (B) and at f r a c t i o n #41 (C). Figure 6. E l e c t r o n micrograph of resuspended high speed p e l l e t f r a c t i o n from E. carotovora s t r a i n s 379 (A) and 440 (B). Table 8. Detection of s e n s i t i v e s t r a i n s of E r w i n i a carotovora subsp. a t r o s e p t i c a a f t e r 48 h incubation i n dual broth c u l t u r e s with d i f f e r e n t s t a r t i n g r a t i o s of Erw i n i a carotovora subsp. carotovora serogroup XI Detection at s t a r t i n g r a t i o s of producer to s e n s i t i v e s t r a i n s S e n s i t i v e S t r a i n s i n s t r a i n s and serogroup XI serogroups 100:1 10:1 1:1 1:10 1:100 1:1000 " T y p i c a l producer" 379 SR8 504 530 496 (I) (XVIII) (XX) (XXII) " D i f f e r e n t i a l producers" 373 SR8 504 530 496 (I) (XVIII) (XX) (XXII) + + 440 SR8 504 530 496 (I) (XVIII) (XX) (XXII) + + + + + + + + + + + + + + + + + "Non-producer" 626 SR8 504 530 496 (I) (XVIII) (XX) (XXII) + + + + + + + + + + + + + + + + + + + + +. + + + - no detectable growth of Erwinia carotovora subsp. a t r o s e p t i c a on a-MG-TZC medium a f t e r 72 h. Results of two r e p l i c a t e s i n each of two experiments. + growth of Erw i n i a carotovora subsp. a t r o s e p t i c a detected on a-MG-TZ medium a f t e r 72 h. Results of at l e a s t two r e p l i c a t e s i n each of two experiments. spectrum of _in v i t r o antagonism f o r the " d i f f e r e n t i a l producers" v a r i e d between s t r a i n s . " D i f f e r e n t i a l producer" s t r a i n 373 was g e n e r a l l y more a n t a g o n i s t i c than s t r a i n 440 and both displayed a completely d i f f e r e n t a c t i v i t y spectrum against the s e n s i t i v e s t r a i n s . Growth of s t r a i n s SR8, 504 and 496 was not detected i n the mixed c u l t u r e s with " d i f f e r e n t i a l producer" s t r a i n 373 at the low s t a r t i n g r a t i o s (1:100 or 1:1000) of producer to s e n s i t i v e c e l l s . A higher s t a r t i n g r a t i o of producer to s e n s i t i v e c e l l s (1:1 or higher) was needed to e l i m i n a t e the growth of the l a t t e r i n mixed c u l t u r e s of s t r a i n 373 against 504 and s t r a i n 440 against SR8, 530 and 496. " D i f f e r e n t i a l producer" s t r a i n 440 was not an e f f e c t i v e antagonist against s t r a i n 504. By c o n t r a s t the "non-producer" permitted the growth of a l l the s e n s i t i v e s t r a i n s even at the highest s t a r t i n g r a t i o (100:1) of the former to the l a t t e r . Because of the apparently longer l a g phase of Eca compared to Ecc (Figure 7) the r a t i o s a f t e r 48 h i n mixed c u l t u r e s would not be l e s s than those at s t a r t i n g time. When mixed c u l t u r e s were in o c u l a t e d onto potato d i s c s , a pattern of antagonism s i m i l a r to that i n dual broth c u l t u r e s was observed (Table 9 ) . Depending upon the producer s t r a i n s and the s e n s i t i v e s t r a i n s employed, the growth of the s e n s i t i v e s t r a i n was completely i n h i b i t e d by a s t a r t i n g r a t i o of one " t y p i c a l producer" to 100 or 1000 s e n s i t i v e c e l l s . By c o n t r a s t the non-producing s t r a i n 626 at a s t a r t i n g r a t i o of 100 to one d i d not prevent growth and d e t e c t i o n of the s e n s i t i v e i n d i c a t o r s t r a i n . 0.7-i 5 10 15 20 25 30 35 T I M E ( I t ) Figure 7. Growth curves f o r s t r a i n s 379 and 626 Er w i n i a carotovora subsp. carotovora) and s t r a i n 530 (Erwinia carotovora subsp. a t r o s e p t i c a ) i n n u t r i e n t broth at two d i f f e r e n t temperatures. - w _ Table 9. Detection of s e n s i t i v e s t r a i n s of Erw i n i a carotovora subsp. a t r o s e p t i c a i n potato d i s c s 48 h a f t e r i n o c u l a t i o n with mixed c u l t u r e s containing d i f f e r e n t s t a r t i n g r a t i o s of Erwinia carotovora subsp. carotovora serogroup XI Detection at s t a r t i n g r a t i o s of producer to s e n s i t i v e s t r a i n s Non-Producer producer S e n s i t i v e s t r a i n s t r a i n s s t r a i n 100:1 10:1 1:1 1:10 1:100 1:1000 379 20,626 530 530 385 496 _ _ _ _ _ + 371 496 + + + + + + - no detectable growth of Erwinia carotovora subsp. a t r o s e p t i c a on oc-MG-TZC medium a f t e r 72 h~ Two r e p l i c a t e s i n each of two separate experiment. + growth of Erw i n i a carotovora subsp. a t r o s e p t i c a on oc-MG-TZC medium a f t e r 72 h. Results of at l e a s t two r e p l i c a t e s i n each of two separate experiments. DISCUSSION A. Screening and Detection Based on the one or two r e p r e s e n t a t i v e s t r a i n s from each serogroup used i n the p r e l i m i n a r y screening and d e t e c t i o n experiments, b a c t e r i o c i n production v a r i e d among serogroups (Table 1). Only s t r a i n s which were biochemically Ecc produced b a c t e r i o c i n s . Campbell and Echandi (1979) reported that both Eca and Ecc were able to produce b a c t e r i o c i n s spontaneously i n n a t u r a l media which suggests that b a c t e r i o c i n production i s not a subspecies c h a r a c t e r i s t i c . However, t h e i r observation was not confirmed i n the present work. B a c t e r i o c i n production by s t r a i n s i n serogroup V, IX and XI was observed which confirmed the report of Crowley and De Boer (1980). In a d d i t i o n a r e p r e s e n t a t i v e s t r a i n i n serogroup XXI, not test e d i n the previous r e p o r t , was also shown to be a b a c t e r i o c i n producer. A l l serogroups containing Eca s t r a i n s and some serogroups co n t a i n i n g Ecc s t r a i n s were s e n s i t i v e to one or more b a c t e r i o c i n s of the producing s t r a i n s (Table 1). Eca s t r a i n s i n two new serogroups t e s t e d i n t h i s study were also observed to be s e n s i t i v e , non-producers. S e n s i t i v i t y of s t r a i n s w i t h i n serogroups was sometimes found to be v a r i a b l e i n those instances where two r e p r e s e n t a t i v e s t r a i n s i n each serogroup were t e s t e d . Some s t r a i n s had a wide s e n s i t i v i t y s p e c t r a . For example, most s t r a i n s i n serogroups I , I I I , V and XXII were s e n s i t i v e to b a c t e r i o c i n s produced by s t r a i n s i n sev e r a l d i f f e r e n t serogroups. By contrast,some s t r a i n s had a narrow s e n s i t i v i t y s p e c t r a . For example re p r e s e n t a t i v e s t r a i n s i n serogroups V, XVIII and IV were s e n s i t i v e to only b a c t e r i o c i n s produced by s t r a i n s i n serogroups I I I , XI and XXI r e s p e c t i v e l y . In a d d i t i o n one or two re p r e s e n t a t i v e s t r a i n s i n each of four serogroups were s e n s i t i v e to the b a c t e r i o c i n s produced by s t r a i n s i n serogroups XI and XXI. De t a i l e d i n v e s t i g a t i o n of seve r a l s t r a i n s i n one Ecc and four Eca serogroups suggested that b a c t e r i o c i n production and s e n s i t i v i t y i n these s t r a i n s at l e a s t , was a serogroup c h a r a c t e r i s t i c (Table 2 ) . The f a c t that serogroup XVIII s t r a i n s which were e i t h e r Eca or Ecc reacted s i m i l a r l y f u r t h e r supported the conclusion that b a c t e r i o c i n s e n s i t i v i t y i s a serogroup c h a r a c t e r i s t i c rather than a subspecies c h a r a c t e r i s t i c . There i s no conclusive evidence that the a b i l i t y to produce b a c t e r i o c i n s plays a major r o l e i n r e g u l a t i n g the occurence of the predominant serogroups i n nature. Several l i n e s of evidence do not support t h i s hypothesis. The most common serogroup (I) i s b a c t e r i o c i n s e n s i t i v e and a non-producer. Another common serogroup ( I I I ) i s als o b a c t e r i o c i n s e n s i t i v e but produces a b a c t e r i o c i n to which only a rarely-found serogroup i s s e n s i t i v e . In a d d i t i o n s t r a i n s i n three r a r e l y - i s o l a t e d serogroups (XXI, IV and V) were b a c t e r i o c i n producers. However, some evidence supporting the hypothesis was also obtained. S t r a i n s i n three common serogroups (IX, XI and XVI) were b a c t e r i o c i n producers and were n o n - s e n s i t i v e . Also s t r a i n s i n the r a r e l y - i s o l a t e d serogroups (XVIII and XX and XXII) were a l l s e n s i t i v e non-producers. I t i s p o s s i b l e that b a c t e r i o c i n s may play a r o l e i n the d i s t r i b u t i o n of only c e r t a i n serogroups but do not represent a general mechanism i n a l l . Some s t r a i n s p r e v i o u s l y reported by Crowley and De Boer (1980) to be non-producers d i d produce b a c t e r i o c i n s i n t h i s study. S t r a i n 95 ( i d e n t i c a l to s t r a i n 195 i n the previous study) was reported to be a non-producer, s e n s i t i v e to producer s t r a i n s i n serogroups V, IX, XI and X I I . The present work confirmed the s e n s i t i v i t y towards the f i r s t three i s o l a t e s (the fo u r t h was not t e s t e d ) . However s t r a i n 95 was found to be a producer against serogroup V s t r a i n s . S i m i l a r l y , s t r a i n s 14 ( i d e n t i c a l to s t r a i n 190 i n the previous study) and 315 ( i d e n t i c a l to s t r a i n 94 i n the previous study) i n serogroup IV and XVI r e s p e c t i v e l y were reported as being ne i t h e r s e n s i t i v e nor producer s t r a i n s but both were found to be a n t a g o n i s t i c against s t r a i n s i n serogroup I I I and V (Table 1). S t r a i n s 90 and 94 i n serogroup V were not s e n s i t i v e to producer s t r a i n 385 (serogroup XI) or producer s t r a i n 84 (serogroup I X ) . Such a r e s u l t i s not unexpected with s t r a i n 385 sin c e Crowley and De Boer (1980) found that only 14% of the s t r a i n s i n serogroup V were s e n s i t i v e to t h i s s t r a i n . However, the observed i n s e n s i t i v i t y to s t r a i n 84 where Crowley and De Boer (1980) had p r e v i o u s l y found 100% of the s t r a i n s t e s t e d i n serogroup V to be s e n s i t i v e was not expected. Since s t r a i n 84 did produce b a c t e r i o c i n which was detected by i n d i c a t o r s t r a i n s SR8, 95 and 555, the reason f o r the i n s e n s i t i v i t y of s t r a i n s i n serogroup V i s not known. S i m i l a r l y , s t r a i n SR8 (serogroup I) was s e n s i t i v e to s t r a i n 84 ( i d e n t i c a l to s t r a i n 63 i n the previous study) but none of the 13 s t r a i n s i n serogroup I test e d by Crowley and De Boer (1980) was s e n s i t i v e to i t . The di s c r e p a n c i e s with the previous report may be due to the p o s s i b i l i t y that some of the s t r a i n s l o s t the plasmids which confer b a c t e r i o c i n production. The plasmids determining a v a r i e t y of p r o p e r t i e s i n many d i f f e r e n t b a c t e r i a are g e n e r a l l y s t a b l e ( E l w e l l and S h i p l e y 1980). However, plasmids are t r a n s f e r a b l e ( E l l i s and Kerr 1978; Broda 1979) and are l o s t at higher rates than normal mutation frequency (Broda 1979). Temperature of incubation may al s o have some e f f e c t on d e t e c t i o n . In one instance when c u l t u r e s were incubated a c c i d e n t l y at 32°C, poor or no i n h i b i t i o n zones was observed. By contrast incubation at 26°C gave good i n h i b i t i o n zones. Crowley and De Boer (1980) used 28°C. Whether reduced production due to the 2°C temperature d i f f e r e n c e was another reason f o r the dis c r e p a n c i e s remains to be determined. However, Vidaver et a l . (1972) have reported that the optimum growth temperature (28 to 32°C) of some Pseudomonas spp. was higher than the optimum temperature f o r b a c t e r i o c i n production (20 to 24°C). A thorough i n v e s t i g a t i o n of the i n t e r a c t i o n between re p r e s e n t a t i v e s t r a i n s i n the four Eca serogroups against a n a t u r a l population of s t r a i n s i n serogroup XI i n d i c a t e d that both b a c t e r i o c i n s e n s i t i v i t y and spontaneous production were not absolute serogroup c h a r a c t e r i s t i c s . V a r i a b i l i t y i n the s e n s i t i v i t y of s t r a i n s i n serogroup I and XVIII was not reported by Crowley and De Boer (1980) but was common i n the other serogroups studied by them. The f a c t that the present study showed v a r i a b i l i t y i n both plus the two a d d i t i o n a l Eca serogroups was probably because 44 producing s t r a i n s i n serogroup XI were tested instead of j u s t one s t r a i n as used by them. This v a r i a b i l i t y was used to group the population of serogroup XI s t r a i n s i i n t o " t y p i c a l " , " d i f f e r e n t i a l " and "non-producer" s t r a i n s . Since b a c t e r i o c i n production could be enhanced i n " d i f f e r e n t i a l producers" by both UV and Mitomycin C and induced i n "non-producer" s t r a i n s by Mitomycin C, the a b i l i t y to produce b a c t e r i o c i n s may w e l l be a serogroup c h a r a c t e r i s t i c . Apparently, the expression of t h i s p o t e n t i a l seems to have been l o s t i n some s t r a i n s . Demonstration of b a c t e r i o c i n production by the same s t r a i n v a r i e d depending upon the techniques used (Tables 4 an 5 ) . For the purpose of d e t e c t i o n alone, the agar overlay technique was more s e n s i t i v e than the spot assay from the c u l t u r e f i l t r a t e of the uninduced c u l t u r e p r e p a r a t i o n s . There are several reasons f o r t h i s observation. In the agar overlay technique growth of the producer c e l l s i s concentrated i n a small area maximizing the concentration of b a c t e r i o c i n . B a c t e r i o c i n production i n broth c u l t u r e s by c o n t r a s t was d i s t r i b u t e d i n a l a r g e volume that d i l u t e d the a c t u a l amount released by the producers. However, the p o t e n t i a l f o r q u a n t i f y i n g the concentration of b a c t e r i o c i n s produced by determining the d i l u t i o n end-point, makes the spot assay technique e s p e c i a l l y u s e f u l with h i g h - t i t r e d preparations recovered a f t e r i n d u c t i o n or p u r i f i c a t i o n . The spot assay method i s also h i g h l y r e p r o d u c i b l e under standardised experimental c o n d i t i o n s (Mayr-Harting et^ a l . 1972). The a r b i t r a r y numerical r a t i n g s given i n the agar overlay technique f o r the degree of i n h i b i t i o n d i d not correspond to the t i t r e of b a c t e r i o c i n produced i n broth c u l t u r e s as shown by the d i l u t i o n end-points i n the spot assay. B a c t e r i o c i n produced by s t r a i n 379 tested against 504 gave a 3.5 r a t i n g whereas against s t r a i n SR8, i t gave a 5 r a t i n g . Assuming that the same r e l a t i v e production occurs i n l i q u i d and s o l i d media the 3.5 r a t i n g had i n f a c t three f o l d higher b a c t e r i o c i n t i t r e than the 5 r a t i n g i n uninduced c u l t u r e . This r e s u l t showed that the degree of c l e a r i n g i n the agar overlay technique was not a good parameter i n q u a n t i f y i n g b a c t e r i o c i n production. The spot assay technique was a more accurate q u a n t i t a t i v e measurement of the b a c t e r i o c i n t i t r e . However, i n d u c t i o n was necessary since only small amounts were produced i n uninduced c u l t u r e s (Table 5 ) . Although b a c t e r i o c i n production was induced by both UV and Mitomycin C, the l a t t e r was p r e f e r r e d f o r s e v e r a l reasons. Only Mitomycin C was able to induce the non-producer s t r a i n s to produce b a c t e r i o c i n (Table 3 ) . Optimum UV l i g h t exposure (as determined by Crowley and De Boer 1980) did not r e s u l t i n detectable b a c t e r i o c i n production i n the non-producer s t r a i n . Mitomycin C was more convenient to use since i t involved the a d d i t i o n of the chemical to e x p o n e n t i a l l y growing c u l t u r e s . I t also provided a more uniform contact with the i n d i v i d u a l c e l l s . By c o n t r a s t , only c e l l s on the surface have greater access to the UV l i g h t exposure. Echandi and Moyer (1979) found that the duration of UV exposure was c r u c i a l because greater or l e s s than 30 s or 60 s (depending on s t r a i n s ) a c t u a l l y reduced the b a c t e r i o c i n t i t r e . Haag and Vidaver (1974) working with S y r i n g a c i n 4-A production by Pseudomonas syringae s t r a i n 4-A also found that Mitomycin C induced 100 f o l d more b a c t e r i o c i n a c t i v i t y compared to i n d u c t i o n using UV l i g h t . D i f f e r e n t optimum f i n a l concentrations of Mitomycin C (0.2 - 0.8 yg/ml) were found to induce maximum b a c t e r i o c i n production depending on the combination of producer and s e n s i t i v e s t r a i n s (Table 6 ) . The optimum f i n a l concentration of Mitomycin C i n other s t u d i e s also v a r i e d , 0.8 - 1.0 yg/ml f o r P. syringae (Haag and Vidaver 1974) and 1 yg/ml f o r Corynebacterium michiganense (Echandi 1976). When higher f i n a l concentrations of Mitomycin C (1.0 - 2.5 yg/ml) were used, the b a c t e r i o c i n production by E_. chrysanthemi l e v e l l e d o f f (Echandi and Moyer 1979). S i m i l a r patterns were observed i n t h i s study. B. P a r t i a l P u r i f i c a t i o n P a r t i a l p u r i f i c a t i o n and concentration of the b a c t e r i o c i n s produced by s t r a i n s i n serogroup XI r e s u l t e d i n b a c t e r i o l y t i c a c t i v i t y being detected i n both the supernatant and resuspended p e l l e t f r a c t i o n s f o l l o w i n g u l t r a c e n t r i f u g a t i o n . A c t i v i t y was not detected i n the p e l l e t f r a c t i o n s r e s u l t i n g from a 1 h c e n t r i f u g a t i o n at 100 000 x £ and 120 000 x £ as reported by Itoh et a l . (1978) and Crowley and De Boer (1980). However, high b a c t e r i o l y t i c a c t i v i t y was obtained i n the resuspended p e l l e t f r a c t i o n s a f t e r a 90 min u l t r a c e n t r i f u g a t i o n at 150 000 x g and t y p i c a l bacteriophage t a i l - l i k e p a r t i c l e s (139 x 20 mm) were observed by e l e c t r o n microscopy. The dimensions of the p a r t i c l e s estimated from the elecron micrographs i n the report by Itoh et a l . (1978) and Crowley and De Boer (1980) were 176 x 20 mm and 156 x 20 mm r e s p e c t i v e l y . The f a c t that the p a r t i c l e s i z e c a l c u l a t e d i n t h i s work was smaller might e x p l a i n why a c t i v i t y was not detected at the lower c e n t r i f u g a t i o n speeds. Production of r a p i d l y d i f f u s i n g small molecular weight b a c t e r i o c i n s as w e l l as the macromolecular type by a s i n g l e s t r a i n of E_. carotovora was pr e v i o u s l y noted by Crowley and De Boer (1980). Production of e i t h e r one type or the other by d i f f e r e n t s t r a i n s of E. carotovora has also been reported by Campbell and Echandi (1979). However, t h i s i s the f i r s t r e p o r t , c l e a r l y e s t a b l i s h i n g the production of both types of b a c t e r i o c i n s i n a s i n g l e s t r a i n of E. carotovora. The b a c t e r i o l y t i c a c t i v i t y i n the supernatant was resolved i n t o components which gave d i s t i n c t l y d i f f e r e n t r e a c t i o n s i n the spot assay. Both n o n - d i f f u s i n g c l e a r zones of i n h i b i t i o n and spreading d i f f u s e zones of i n h i b i t i o n were observed. A high molecular weight component which was excluded from a Sephadex G-200 column and eluted o f f f i r s t on a Sephacryl S-300 column was r e s p o n s i b l e f o r the c l e a r i n h i b i t i o n zones. The estimated molecular weight (224 500 D) corresponded with the n o n - d i f f u s i b i l i t y observed. The second peak of a c t i v i t y eluted from Sephacryl S-300 gave only d i f f u s e i n h i b i t i o n zones. R e c i p r o c a l d i l u t i o n end-points of the b a c t e r i o c i n a c t i v i t y of each f r a c t i o n suggested that there were two peaks which were not w e l l separated by t h i s column. The d i l u t i o n end-points between p e l l e t f r a c t i o n s and the supernatants, while not s t r i c t l y comparable due to d i f f e r e n c e s i n volume, would suggest that the macromolecular bacteriophage t a i l - l i k e p a r t i c l e s are r e s p o n s i b l e f o r most of the b a c t e r i o l y t i c a c t i v i t y . The high-speed supernatant f r a c t i o n s were c l a s s i f i e d as " b a c t e r i o c i n - l i k e " compounds because they were a c t i v e against c l o s e l y r e l a t e d s t r a i n s but not a c t i v e against the producing s t r a i n s . The b a c t e r i o l y t i c a c t i v i t y was also not due to r e s i d u a l Mitomycin C. The d i f f u s e zones were detected only i n the spot assays from induced c u l t u r e preparations a f t e r p a r t i a l p u r i f i c a t i o n and c o n c e n t r a t i o n . This suggests that the small molecular weight " b a c t e r i o c i n - l i k e " compounds are e i t h e r produced i n low concentration and are not detected by the s e n s i t i v e i n d i c a t o r s t r a i n s or that they are perhaps breakdown products of the macromolecular b a c t e r i o c i n s . However, Itoh et^ a K (1978) reported that denatured c a r o t o v o r i c i n Er i s e a s i l y digested by t r y p s i n whereas " b a c t e r i o c i n - l i k e " compounds described i n the present study were t r y p s i n r e s i s t a n t . A l l four b a c t e r i o l y t i c f r a c t i o n s (the macromolecular phage t a i l - l i k e p a r t i c l e s plus three " b a c t e r i o c i n - l i k e " components were produced i n d i f f e r e n t concentrations by a l l types of serogroup XI (Table 6 ) . Production by the " t y p i c a l producer" was highest and the "non-producer"the lowest. A l a r g e r quantity of the " b a c t e r i o c i n - l i k e " components i s needed to confirm the i n s e n s i t i v i t y of the i n d i c a t o r s t r a i n s SR8 and 496 to the b a c t e r i o c i n s induced i n the "non-producers". C. Dual C u l t u r e Studies Dual c u l t u r e s t u d i e s c l e a r l y i n d i c a t e d that when producer and i n d i c a t o r s t r a i n s were growing together, i n h i b i t i o n of the s e n s i t i v e s t r a i n s occurred. The f a c t that s t a r t i n g r a t i o s of one producer to 100 or 1000 s e n s i t i v e c e l l s r e s u l t e d i n i n h i b i t i o n by the " t y p i c a l producer" s t r a i n and a r a t i o of 100 "non-producer" to one s e n s i t i v e c e l l d i d not prevent d e t e c t i o n of the l a t t e r e l i m i n a t e s n u t r i e n t competition as the mechanism of i n h i b i t i o n . Since the producers and the "non-producers" have s i m i l a r growth rates (Figure 2 ) , the a n t a g o n i s t i c behaviour observed with the producers probably i s due to the production of b a c t e r i o c i n s . While b a c t e r i o c i n a c t i v i t y i t s e l f was not monitored i n e i t h e r the dual c u l t u r e s or potato d i s c experiments, b a c t e r i o c i n production i n s i m i l a r broth c u l t u r e s have been demonstrated i n other experiments (Table 5 and 6 ) . The demonstrated a b i l i t y of the " t y p i c a l producer" s t r a i n s (serogroup XI) to antagonise a l a r g e number of s e n s i t i v e c e l l s would give the producing s t r a i n s a s e l e c t i v e advantage i n nature and be i d e a l l y s u i t e d f o r use i n b i o l o g i c a l c o n t r o l work. In the A. radiobacter - A. tumefaciens system at l e a s t a one to one r a t i o of non-pathogenic b a c t e r i o c i n producer to pathogenic c e l l s was needed to r e s u l t i n complete p r o t e c t i o n from crown g a l l . Since J£. carotovora i s pathogenic to potato the idea of using v i r u l e n t , b a c t e r i o c i n - p r o d u c i n g s t r a i n s to c o n t r o l disease i s not a t t r a c t i v e . A p o s s i b l e a l t e r n a t i v e would be to use p u r i f i e d b a c t e r i o c i n preparations. P a r t i a l l y p u r i f i e d b a c t e r i o c i n from IE. carotovora applied p r i o r to i n o c u l a t i o n with the pathogen has been reported by Campbell and Echandi (1979) to c o n t r o l s o f t rot on potato s l i c e s in_ v i t r o . The same preparation f a i l e d to c o n t r o l s o f t r o t of whole n a t u r a l l y - i n f e s t e d potato tubers. P u r i f i e d S y r i n g a c i n 4-A, a b a c t e r i o c i n produced by Pseudomonas syringae s t r a i n 4-A, has been used experimentally to c o n t r o l P_. p h a s e o l i c o l a s t r a i n BE and f o r seed treatment against P_. g l y c i n e a (Vidaver 1976). B a c t e r i o c i n s have the p o t e n t i a l of being an e f f e c t i v e b i o l o g i c a l c o n t r o l against the s e n s i t i v e s t r a i n s i n the long run since they are more acceptable environmentally and more s e l e c t i v e against the target organisms than very broad-spectrum chemicals and a n t i b i o t i c s . There i s a l s o a p o s s i b i l i t y of expanding the a b i l i t y to produce b a c t e r i o c i n s i n non-producer s t r a i n s . In Agrobacterium the b a c t e r i o c i n o g e n i c f a c t o r has been shown to be coded by plasmid genes (Sciaky j^t 1978; Merlo and Nester 1977). This plasmid i s a l s o t r a n s f e r a b l e i n the presence of nopaline which behaves as a promoter ( E l l i s and Kerr 1978). I f s i m i l a r plasmids e x i s t i n the E_. carotovora system, the p o t e n t i a l e x i s t s f o r i n t r o d u c i n g the genes determining production of various b a c t e r i o c i n s i n t o a s i n g l e s t r a i n . Through genetic engineering, a non-pathogenic i d e a l antagonist producing b a c t e r i o c i n s with a wide a c t i v i t y spectrum may be created. However, the d e l e t i o n of other c h a r a c t e r i s t i c s enabling s u r v i v a l of the b a c t e r i a i n nature should not be ignored. SUMMARY 1. B a c t e r i o c i n production by s t r a i n s i n serogroup XI (Ecc) and b a c t e r i o c i n s e n s i t i v i t y of s t r a i n s i n serogroups I , XVI I I , XX and XXII (Eca) were ge n e r a l l y a serogroup c h a r a c t e r i s t i c . 2. A l l Ecc s t r a i n s tested were b a c t e r i o c i n producers at l e a s t a f t e r mitomycin C i n d u c t i o n . 3. Some Ecc s t r a i n s were both b a c t e r i o c i n s e n s i t i v e as w e l l as being b a c t e r i o c i n producers. 4. A l l Eca s t r a i n s tested regardless of serogroup were b a c t e r i o c i n s e n s i t i v e and non producers. 5 . Production of and s e n s i t i v i t y to b a c t e r i o c i n s were not c o r r e l a t e d with the frequency of d i s t r i b u t i o n of s t r a i n s i n the most commonly i s o l a t e d serogroups (I and I I I ) i n B r i t i s h Columbia. 7 . 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