Contributions of Individual σ B -Dependent General Stress Genes to Oxidative Stress Resistance of Bacillus subtilis

Abstract

ABSTRACT The general stress regulon of Bacillus subtilis comprises approximately 200 genes and is under the control of the alternative sigma factor σ B . The activation of σ B occurs in response to multiple physical stress stimuli as well as energy starvation conditions. The expression of the general stress proteins provides growing and stationary nonsporulating vegetative cells with nonspecific 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 the development of resistance against exposure to the superoxide-generating agent paraquat and hydrogen peroxide (H 2 O 2 ). In fact, 62 mutants displayed significantly decreased survival rates in response to paraquat and/or H 2 O 2 stress compared to the wild type at a confidence level of an α value of ≤0.01. Thus, we were able to assign 47 general stress genes to survival against superoxide, 6 genes to protection from H 2 O 2 stress, and 9 genes to the survival against 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 support the notion that different severe physical stress stimuli elicit a common secondary oxidative stress.