The Mycobacterium tuberculosis sigJ gene controls sensitivity of the bacterium to hydrogen peroxide

Sigma factors are important global regulators which control bacterial gene expression during growth and in response to stress. Previous work showed that mRNA of the sigJ gene was up-regulated in late stationary-phase and after rifampicin treatment. In order to verify the function of SigJ, we constructed a Mycobacterium tuberculosis mutant lacking the sigJ gene. In a microaerophilic stationary-phase model, the sigJ mutant showed the same growth pattern as the wild-type strain. In an immune stasis murine model in which the bacterial number plateaued between the second and the 15th week, the mutant showed a similar growth curve to the wild-type strain. However, the sigJ mutant was more susceptible to killing by H2O2 than its parental strain. The parental level of sensitivity to H2O2 was recovered in the sigJ complemented strain. These data suggest that the SigJ protein is not essential for survival in long-term stationary phase or in bacterial stasis in mice. However, the sigJ gene may control an alternative H2O2 resistance pathway.