NONSPECIFIC, GENERAL AND MULTIPLE STRESS RESISTANCE OF GROWTH-RESTRICTED BACILLUS-SUBTILIS CELLS BY THE EXPRESSION OF THE SIGMA(B) REGULON

Bacillus subtilis cells respond almost immediately to different stress conditions by increasing the production of general stress proteins (G SPs), The genes encoding the majority of the GSPs that are induced by heat, ethanol, salt stress or by starvation for glucose, oxygen or pho sphate belong to the sigma(B)-dependent general stress regulon, Despit e a good understanding of the complex regulation of the activity of si gma(B) and knowledge of a Very large number of general stress genes co ntrolled by sigma(B), first insights into the physiological role of th is nonspecific stress response have been obtained only very recently. To explore the physiological role of this regulon, we and others ident ified sigma(B)-dependent general stress genes and compared the stress tolerance of wild-type cells with mutants lacking sigma(B) or general stress proteins. The proteins encoded by sigma(B)-dependent general st ress genes can be divided into at least five functional groups that mo st probably provide growth-restricted B, subtilis cells with a multipl e stress resistance in anticipation of future stress, In particular, s igB mutants are impaired in non-specific resistance to oxidative stres s, which requires the sigma(B)-dependent dps gene encoding a DNA-prote cting protein. Protection against oxidative damage of membranes, prote ins or DNA could be the most essential component of sigma(B)-mediated general stress resistance in growth-arrested aerobic Gram-positive bac teria, Other general stress genes have both a sigma(B)-dependent induc tion pathway and a second sigma(B)-independent mechanism of stress ind uction, thereby partially compensating for a sigma(B) deficiency in a sigB mutant, In contrast to sigB mutants, null mutations in genes enco ding those proteins, such as clpP or clpC, cause extreme sensitivity t o salt or heat.