Changes of sensitivity to heat shock during logarithmic growth of Bacillus subtilis.

The effect of heat shock on B. subtilis was found to vary within the logarithmic growth phase. Depending on the age of the culture, all cells, or as little as less than 1% of the population, may survive heating for 6 min at 54 degrees C. These characteristic changes in sensitivity to heat shock were observed with B. subtilis grown on various media, as well as with E. coli. The increased sensitivity of B. subtilis to heat shock was observed within a rather narrow time span in the log phase. Preheating at 45 degrees C had a protective effect on the samples collected at the time of greatest heat sensitivity. It is suggested that besides heat shock proteins other factors are also involved in the processes leading to survival after heat shock.