In Bacillus subtilis, heat shock proteins can be classified into two main groups: specific heat shock proteins (about 5) and general stress proteins (at least 14). Salt stress was very effective in the induction of general stress proteins (5 to 50-fold stimulation), but the synthesis of heat-specific stress proteins was not stimulated. Furthermore there were some proteins whose synthesis was accelerated only by salt stress.

Salt-induced changes in protein synthesis were investigated in the cyanobacterium Synechcystis sp. PCC 6803. Immediately after a salt shock of 684 mM-NaC1, total protein synthesis was almost completely blocked. Then, parallel to the accumulation of the osmoprotective compound glucosylglycerol, protein synthesis recovered gradually but remained diminished. The activation of glucosylglycerol synthesis was not inhibited by chloramphenicol at concentrations which totally inhibited protein synthesis. The qualitative protein composition of salt-shocked and control cells was similar. However, the rates of synthesis of single proteins were altered in cells shocked for 10 h and adapted to high salt conditions. Using two-dimensional gel electrophoresis, proteins were found which were synthesized at enhanced rates after adding salt.

The permissive temperature for sporulation of Bacillus rnegateriurn 27 (up to 42 "C) was found to be 4-5 "C lower than that for growth. The non-permissive temperature suppressed the initial phases of sporulation characterized by the synthesis of an extracellular proteinase but the cells retained the ability to sporulate for several hours. Neither growth at supraoptimal temperatures nor heat shock applied at the end of the growth phase increased the permissive sporulation temperature. The organism synthesized at least ten heat-shock proteins, the dominant one being HSP 69. These proteins were also found in cells after 3 h of incubation at 43.5 "C but their presence did not ensure the ability to sporulate at this temperature. The rise of temperature provoked an imbalance between synthesis and degradation of cellular proteins, whose role in suppression of sporulation is discussed.

Some of the presumable heat shock proteins will be produced in Bacillus subtilis in response to different environmental conditions, e.g. heat shock, amino acid limitation or oxygen limitation. During amino acid limitation or during oxygen limitation the relA+ strain is able of synthesizing this set of proteins but the relA strain is not. We suggest that the accelerated rate of the synthesis of some heat shock proteins depends on the induction of the stringent response because the (p)ppGpp production does not occur in the relA strain during amino acid or oxygen limitation. On the other hand the relA strain can produce heat shock proteins under heat stress. Therefore different mechanisms must be responsible for the expression of this set of genes during heat and other stress stimuli. It can be supposed that in B. subtilis the (p)ppGpp-dependent stringent control is a central defense reaction against different adverse environmental conditions and furthermore, that the synthesis of “stress” proteins as an essential component of the stringent response is part of a general adaptation mechanism under non-growing conditions.

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