HEAT-SHOCK APPLIED EARLY IN SPORULATION AFFECTS HEAT-RESISTANCE OF BACILLUS-MEGATERIUM SPORES

Cells of Bacillus megaterium 27 were challenged by a 30-min heat shock at 45-degrees-C during various sporulation stages and then shifted ba ck to a temperature permissive for sporulation (27-degrees-C), at whic h they developed spores. Heat shock applied at 120 min after the end o f the exponential phase induced synthesis of heat shock proteins (HSPs ) in the sporangia and delayed the inactivation of spores at 85-degree s-C. Several HSPs, mainly HSP 70, could be detected in the cytoplasm o f these spores. An analogous HSP, the main HSP induced by increased te mperature during growth, belongs to the GroEL group according to its N -terminal sequence. The identity of this protein was confirmed by West ern blot (immunoblot) analysis with polyclonal antibodies against B. s ubtilis GroEL. Sporangia treated by heat shock immediately or 240 min after exponential phase also synthesized HSPs, but none of them could be detected in the spores in an appreciable amount. These spores showe d only a slightly increased heat resistance.