Graduate Thesis Or Dissertation
 

A comparison of some physiological properties of Bacillus cereus 569R with a mutant strain

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  • The purpose of this investigation was to compare some of the properties of a spore-forming mutant of Bacillus cereus 569R with the wild type. The strains were grown under identical conditions in liquid medium. The mutant, strain 45, was characterized with respect to growth rate, pH changes in the medium, morphological development, cell density during the growth cycle, the effect of oxygen deprivation on the time of spore formation, and the production of an extracellular protease. Strain 45 was found to maintain a higher growth rate than 569R. The pH curves indicated that, in time, strain 45 was about 30 minutes ahead of wild type. Morphologically, strain 45 exhibited no long chain stage characteristic of early logarithmic growth B. cereus 569R. Poly β hydroxybutyrate was accumulated before the sharp rise in pH in 45. This comparatively early synthesis suggested that acetate utilization and polymer synthesis may not be coordinately controlled in this mutant. Spore formation occurred two and one-half hours earlier in strain 45, and the spores were twice as large as spores of wild type. The production of protease in the mutant occurred earlier, and in higher concentration when compared with 569R. The results of these experiments fell into two classes. The first class included growth rate, pH, and cell density shifts. These events occurred approximately one-half hour earlier in cultures of strain 45, and appeared to be correlated with the cell mass. The second class of results--the time of polymer synthesis, the period when the time of sporulation was sensitive to oxygen, the time of protease production, and the time of sporulation- - appeared to be independent of cell mass, and occurred markedly earlier in strain 45. The very early appearance of these sporulation- related events in the culture cycle suggested that the mutant strain 45 may be catabolically derepressed for sporulation. Characterization of two asporogenous mutants of B. cereus 569R was also undertaken.
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