Distribution of sigma factors delineates segregation of virulent and avirulent Mycobacterium

The genus Mycobacterium includes a wide range of species of both slow and rapid growth under major pathogens, opportunists, and saprophytes. The number and combination of sigma factors are extremely diversified among various species of Mycobacterium. The comparative genome analysis illustrates that SigC, SigD, SigG, SigH, SigK and SigI are dominant among the pathogens. Evolutionary analysis using Bayesian inference on 16S rRNA and MLST-based phylogeny using 14 housekeeping genes distinctly differentiate the slow-growing Mycobacterium from fast growers and segregate pathogens from opportunists and saprophytes. Based on the similarity coefficient upon the allotment of sigma factors in mycobacterial species through UPGMA dendrogram analysis, it is apparent that the pathogens are grouped separately following the similar trend observed from the evolutionary approach. Predominance of a set of sigma factors particularly the pathogenic Mycobacterium co-exists with the distribution of six well-known virulence factors of Mycobacterium (PhoP, PcaA, FbpA, Mce1B, KatG and PE_PGRS30). The pathogenicity responsible sigma factors elicit close resemblance with few notable characters of the known virulence factors. Thus the analysis renders that the distribution of sigma factors of different species of Mycobacterium can be a potential tool to predict their pathogenicity index.