Evaluation of the role of sigma B in Mycobacterium smegmatis

The alternate sigma factor, sigB, is known to play a crucial role in maintaining the stationary phase in mycobacteria. In this communication, we have studied the proteomics of Mycobacterium smegmatis mc(2)155 and its two derivatives, one of which has a disrupted sigB gene and the other, PMVSigB, which contains a multicopy plasmid containing sigB. We have identified by two-dimensional gel analyses, several proteins that are over-expressed in PMVSigB compared to mc(2)155. These proteins are either stress proteins or participate actively in different metabolic pathways of the organisms. On the other hand, when sigB deleted mycobacteria were grown until the stationary phase and its two-dimensional protein profile was compared to that of mc(2)155, few DNA binding proteins were found to be up-regulated. We have shown recently that upon over-expressing sigB, the cell surface glycopeptidolipids of M. smegmatis are hyperglycosylated, a situation similar to what was observed for nutritionally starved bacteria. Gene expression profile through quantitative PCR presented here identified a Rhamnosyltransferase responsible for this hyperglycosylation.