Physiological studies of a temperature-sensitive sporulation mutant of Bacillus cereus T

Growth of temperature-sensitive mutant Bacillus cereus T JS22-C occurred normally at the restrictive temperature (37 degrees C), but sporulation was blocked at stage 0. The production of extracellular and intracellular proteases and of alkaline phosphatase occurred at 37 degrees C, but the expression of a functional tricarboxylic acid cycle did not. At the permissive temperature (26 degrees C), the mutant sporulated at a slightly lower frequency (60%) and at a lower rate than the parent strain. The oxidation of organic acids, which accumulate in the growth medium began at T0 in cultures of the parent strain but was delayed until about T3 in cultures of the mutant. Later events in sporulation were also delayed in the mutant by about 3 h. Experiments in which the temperature of growth was shifted from 37 to 26 degrees C or from 26 to 37 degrees C at various times showed that the temperature-sensitive event began approximately 1 h after the end of exponential growth and ended when the cells reached the end of stage II (septum formation). The absence of a functional tricarboxylic acid cycle in cells of the mutant grown at 37 degrees C or shifted from 26 to 37 degrees C before T1 did not appear to be due to a lesion in one of the structural genes of the tricarboxylic acid cycle but was more likely due to the inability of the cells to derepress the synthesis of some of the enzymes of that cycle.