Identification and transcriptional analysis of new members of the σB regulon in Bacillus subtilis

Summary: Bacillus subtilis responds to various stimuli (heat, ethanol and salt stress, energy starvation) with the induction of general stress proteins (GSPs). Most of them belong to the stress and stationary-phase regulon controlled by the alternative sigma factor σB. The majority of σB-dependent proteins are thought to provide a precautionary general stress resistance in stressed or starved cells. In this report, the identification and transcriptional analysis of nine new members of the σB regulon are described. The biochemical function was not determined for any of the proteins encoded by the nine new σB-dependent stress genes, however, similarities to proteins in the databases allowed a distinction between proteins with putative (i-iv) and unknown (v) function. The putative functions of BmrU, YcdF, YdaD, YdaP, YhdN and YocK underline the suggested protective role of σB-dependent GSPs and also elucidate new areas where σB might play an important role. (i) The finding that the bmrUR operon is under σB control indicates that the elimination of multidrug compounds might be a new function in multiple stress resistance. (ii) YcdF and YdaD resemble NAD(P)-dependent dehydrogenases. Both proteins could be involved in the generation of NAD(P)H and therefore in the maintenance of the intracellular redox balance under stress. (iii) The ydaP gene might belong to the increasing number of σB-dependent genes whose orthologues are under the control of σS in Escherichia coli, indicating that both regulons may fulfil similar functions. (iv) YhdN shows weak similarities to potassium ion channel proteins and YocK shows resemblance to the DnaK suppressor protein DksA. (v) Three new σB-dependent genes (ydaE, ydaG and yfkM) encoding proteins with still unknown functions were also described. Further analyses of corresponding mutants might allow a first prediction of their function within the framework of the general stress regulon.