Genes under positive selection in Mycobacterium tuberculosis.

We employed an evolutionary genomics approach to detect genes under lineage-specific positive selection for the two closely related Mycobacterium tuberculosis strains, the virulent H37Rv and the avirulent H37Ra, with the clinical isolate CDC1551 as the outgroup. We found six H37Rv-specific and six H37Ra-specific positively selected genes, among which the former comprised a flavoprotein, a RNA polymerase sigma factor SigM, two PPE family proteins, as well as two hypothetical proteins, while the latter consisted of a dehydrogenase, a (3R)-hydroxyacyl-ACP dehydratase subunit HadA, a PPE family protein, and three PE-PGRS family proteins. Obviously, the PE/PPE/PE-PGRS family proteins were the main targets of positive selection. The functional discussion of our findings implied that those positively selected genes were highly involved in antigen variations and immune evasions of Mycobacterium tuberculosis.