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A correlative study was made of some structural and functional features of a reasonably synchronized culture of Bacillus cereus strain terminalis during spore formation and maturation. The successive stages of development could be recognized by phase contrast microscopy and in electron micrographs of ultra-thin-sectioned cells. Attempts were made to correlate these changes with the acquisition of heat resistance and the synthesis of dipicolinic acid. The outer coat of the spores was observed to be formed first around the forespore; the exosporium, cortex, and inner coat then appeared sequentially and independently of existing sporangial membranes. Dipicolinic acid synthesis began in the early transitional stage, just after forespore formation, and reached one third of the maximum level before an increase of heat resistance in the population was detectable, indicating the possibility of a correlation only above a threshold level of the compound.
Hashimoto et al. (Fri,) studied this question.