The contribution of individual σ ^B-dependent general stress to oxidative stress resistance of Bacillus subtilis

The general stress regulon of Bacillus subtilis comprises approximately 200 genes and is under the control of the alternative sigma factor ÕB. Activation of ÕB occurs in response to multiple physical stress stimuli as well as energy starvation conditions. Expression of the general stress proteins provides growing and stationary non-sporulating vegetative cells with a non-specific and broad stress resistance. A previous comprehensive phenotype screening analysis of 94 general stress gene mutants in response to severe growth inhibiting stress stimuli including ethanol, NaCl, heat, and cold indicated that secondary oxidative stress may be a common component of severe physical stress. Here we tested the individual contributions of the same set of 94 mutants to resistance development against exposure to the superoxide generating agent paraquat and hydrogen peroxid (H2O2). In fact, 62 mutants displayed significantly decreased survival rates in response to paraquat and/or H2O2 stress compared to the wild type at a confidence level of a = 0.01. Thus, we were able to assign 47 general stress genes to survival of superoxide, 6 genes to protection from H2O2 stress and 9 genes to survival of both. Furthermore, we show that a considerable overlap exists between the phenotype clusters previously assumed to be involved in oxidative stress management and the actual group of oxidative stress sensitive mutants. Our data provide information that many general stress proteins with still unknown functions are implicated in oxidative stress resistance and further supports the notion that different severe physical stress stimuli elicit a common secondary oxidative stress.