[Characterization of the expression and function of SigM an ECF sigma factor in mycobacteria]

The survival of M. tuberculosis within the macrophage depends on its ability to respond to oxidative stress, and the ECF subfamily of sigma factors likely play an important role. We studied SigM, a sigma factor whose gene is located near the origin of DNA replication. In both M. smegmatis and M. bovis BCG, the expression of sigM was induced at high temperature and in stationary phase. Mutants of M. smegmatis without an intact sigM were defective for survival in oxidative stress and also for the induction of thioredoxin reductase activity in oxidative stress. The thioredoxin system reduces disulfide bonds that are formed in oxidative stress. SigM thus appears to regulate thioredoxins and forms part of the bacteria's complex protective responses.