Evolution of Developmental Stages in Cultures of Bacillus cereus

SUMMARY: Cultures of Bacillus cereus grown in a chemically defined medium with glucose under standardized conditions followed a reproducible pattern of development giving good spore yields in less than 24 hr. Samples were withdrawn at intervals and individual organisms were classified into developmental states by four methods: (1) Gram reaction; (2) growth potential as revealed by the microcultures derived from single organisms or chains of organisms isolated into microdrops; (3) ability of individual organisms to take up neutral red; (4) electrophoretic distribution of organisms through a pH gradient. From the results we conclude that at most times the population was heterogeneous with respect to state of the organisms and that at least some of the shifts in state were quantal, in the sense that each state was relatively stable and that the transition from one state to the next rapid. There was a cyclical appearance and disappearance of organisms stainable with neutral red. Waves of stainable organisms were correlated with the break-up of chains into smaller units and with the lysis of a proportion of the organisms.