Relationship among oxidative stress, growth cycle, and sporulation in Bacillus subtilis

The sensitivity of Bacillus subtilis to hydrogen peroxide (oxidative stress) was found to vary with the position of the culture in the growth cycle. The most dramatic change occurred at the stationary phase, when the cells became totally resistant to 10 mM H2O2, in contrast to the loss of 3 to 4 log units of viability when treated at the early log phase. Two of the eight proteins induced by a protective concentration of H2O2 (50 muM) were also induced (in the absence of oxidative stress) on entry into the late log phase of growth. The response of five isogenic spo0 mutants (spo0B, spo0E, spo0F, spo0H, and spo0J) to oxidative stress was identical to that of the wild-type parental strain. In an isogenic spo0A strain, mid-log-phase cells were 100-fold less sensitive to 10 mM H2O2 than was the wild type. Pretreatment with 50 microM H2O2 induced little further protection, suggesting that the response is constitutive in this strain. By comparison of proteins induced by 50 microM H2O2 in the wild-type, spo0A, spo0H, and spo0J strains, four proteins were identified that may be essential for protection against lethal concentrations of H2O2. The presence of multiple copies of the spo0H gene in a spo0A background converted the stress phenotype of the spo0A mutant to that of the wild type but left the sporulation phenotype unaltered.