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Physical and chemical studies of the exopolysaccharide isolated from Pseudomonas fragi ATCC 4973

University of British Columbia

Pseudomonas fragi ATCC 4973, inoculated onto meat surfaces and incubated at 21°C, was examined by electron microscopy. Both scanning and transmission electron microscopy revealed an extracellular material (glycocalyx) which appeared to mediate cell-to-cell as well as cell-to-muscle attachment to the meat samples. Transmission electron micrographs of cells grown on solid medium, harvested at the early logarithmic growth phase, revealed bleb-like evaginations or protrusions on the cell surface. Stationary phase cells, however, exhibited no bleb-like evaginations. Fine extracellular material randomly distributed on the cell surface was observed. Transmission electron micrographs of bacterial cells grown in liquid medium, harvested at the early logarithmic growth phase, revealed no blebs or extracellular material. In contrast, stationary phase cells showed only few attached blebs as well as globules adjacent to the cells. The type of substrate (solid vs. liquid) influenced the expression of blebs on the surface of P. fragi cells. An association between the glycocalyx fibres and bleb-like evaginations was also noted. The exocytosic formation of blebs and globules into the immediate environment of the cell appeared to precede the formation of glycocalyx by P. fragi cells. Chemical studies on the isolated glycocalyx of P. fragi indicated a hexosaminoglycan structure. Trif luoroacetic acid and hydrogen fluoride were used in the hydrolysis of the polysaccharide. Quantitative amounts of the individual monosaccharides were obtained from the hydrolysed polysaccharide using preparative paper chromatography. Gas liquid chromatography and mass spectrometry were used in the verification of an N-acetyl amino sugar component. Monomeric units and substituents in the polysaccharide chain were determined by ¹H and ¹³C nuclear magnetic resonance spectroscopy. By methylation analysis, the polysaccharide of P. fragi was shown to consist of a linear repeating trisaccharide unit. The proposed partial hexosaminogly-can structure is: [See Thesis for Diagram]

Text

2010-06-12

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http://hdl.handle.net/2429/25614

Food Science

University of British Columbia

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