Impaired oxidative stress resistance ofBacillus subtilis sigBmutants and the role ofkatAandkatE

Two catalases of B. subtilis have been studied which are subject to two different regulatory mechanisms. Whereas KatA belongs to the group of proteins specifically induced by oxidative stress, KatE is a general delta B-dependent stress protein, not induced by oxidative stress. There are two mechanisms of oxidative stress resistance, the adaptive resistance induced by low H2O2 concentrations and an unspecific resistance acquired in glucose-starved cells. Mutants lacking KatA are defective in the adaptive resistance and both exponentially growing and glucose-starved cells are 100-fold more sensitive against lethal concentrations of H2O2. Under both conditions, however, a katE mutant was just as resistant as the wild type. Therefore, the role of KatE in oxidative stress tolerance remains obscure. sigB mutants which are no longer able to induce delta B-dependent general stress proteins in glucose-starved cells are characterized by a strong impairment in the unspecific oxidative stress resistance but not in the H2O2-induced oxidative stress resistance. This is the first evidence that sigB mutants have an obvious phenotype compared to the wild type and indicates that delta B-dependent general stress proteins may function in providing starving cells with resistance against oxidative stress.