UBC Theses and Dissertations
A preliminary investigation of some of the factors affecting the percentage germination of lyophilized conidia of Aspergillus niger Van Tieg Anastasiou, Joan Diane
Variations of the techniques and materials used during lyophilization procedures are considered for their effect upon the percentage viability of the conidia of Aspergillus niger (van Tieg.) after freeze-drying. Of the factors investigated, those affecting percentage survival are: (1) Age of the culture from which the conidia are harvested. At 24-26°C., maximum survival occurs after two to six days of incubation. (2) The temperature at which the culture is incubated. A temperature of 6°C. slows the loss of viability after lyophilization. (3) The carrier in which the conidia are dried. Solutions containing 20% sucrose allowed the best survival of the diluents tested. 0.5% ascorbic acid depressed viability immediately after drying and after 13 months storage. (4) Degassing the spore suspension before freezing it. This treatment increased survival after lyophilization. This is not a surface phenomenon. (5) The length of time and the temperature at which the conidia are suspended before being frozen. A long period and a high temperature of spore suspension produces a rapid loss of viability after drying. (6) The general method of lyophilization. The Edwards centrifuge method of freeze-drying produces better survival than either of the other two methods described. Those factors which do not significantly affect conidial survival are: (1) Concentration of conidia in the drying suspension. Only a narrow range of dilutions were tested. (2) The length of time from 5 minutes to 10 hours that the suspension is frozen at -50°C. before evacuating.
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