An Intracellular Polysaccharide that Serves as a Carbon and Energy Source for Sporulation in "Bacillus Cereus" Strain T
Holmes, Christopher A.
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The Problem. "Bacillus cereus" strain T accumulates an intracellular polysaccharide during late logarithmic and early stationary phases of the growth cycle. The polysaccharide is subsequently degraded during the sporulation phase of the growth cycle. Initial research suggested that the polysaccharide was used as a carbon and energy storage compound for the completion of sporulation. Subsequent work involved using polysaccharide-minus mutants of the strain to support this hypothesis. This paper details the use of a mutant deficient in its ability to degrade the polysaccharide to verify the original hypothesis. Procedure. Spores of "Baccilus cereus" strain T were treated with the chemical mutagen ethyl methane sulfonate and screened for the ability to accumulate and not degrade the intracellular polysaccharide. A suitable mutant (CH-5) was isolated and compared to the wild-type in terms of growth characteristics, polysaccharide and poly-B-hydroxy butyrate (PHB) accumulation and degradation, spore heat resistance, and the ability to sporulate endotrophically. Findings. The mutant strain (CH-5) demonstrated growth characteristics almost identical to those of the wild-type strain (T). Polysaccharide and PHB accumulation were very similar in both strains under similar conditions but CH-5 was unable to degrade the polysaccharide during spore formation. Mutant spores, produced in the absence of intracellular PHB, were much less heat resistant than wild-type spores produced under the same conditions. The mutant strain was also unable to sporulate endotrophically when grown under conditions preventing PRB accumulation. Conclusions. The intracellular polysaccharide of "Bacillus cereus" strain T functions as a source of carbon and energy for sporulation, especially under conditions preventing PHB accumulation. The polysaccharide also appears to contribute to increased heat resistance of spores, possibly by an osmotic mechanism. Recommendations. It might be of interest to obtain mutants blocked at various stages of sporulation to see what effect this has on polysaccharide accumulation and degradation.
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