EFFECT OF pH ON INTERMEDIATES PRODUCED DURING GROWTH AND SPORULATION OF BACILLUS CEREUS

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Abstract
Cultures of Bacillus cereus strain-T grown in an unbuffered glucose-yeast extract-mineral salts medium and in the same medium buffered at pH 6.4, 7.0 or 7.4 were examined to determine the effect of pH on the production and utilization of metabolic intermediates during growth and sporulation. Although the growth rate of the unbuffered cultures decreased as a result of changes in pH, the growth rates of the buffered cultures were constant and similar. Only slight differences were observed in the final number of spores produced and in the time required for the completion of the sporulation process. Acetic-and lactic-acids were the chief acidic end products of growth in buffered media, in which more than twice the amount of these acids accumulated than was detected in unbuffered cultures. In the latter cultures, pyruvic acid rather than lactic-acid was formed together with acetate. Acetoin also accumulated in the unbuffered cultures, but none was detected in any of the buffered cultures. All of these intermediates were rapidly utilized by the cells once sporulation began. Poly-[beta]-hydroxybutyric-acid accumulation in the cells during the early stages of sporulation was also influenced by pH, with the greatest accumulation of this polymer occurring in the cells grown at pH 6.2 to 6.4. These results support the hypothesis that high polymer content in the cells is not imperative for the completion of sporulation. However, if any is formed, it is completely utilized during the final stages of spore formation.