<i>Mycobacterium tuberculosis</i> novel DNA methyltransferaseenhances mycobacterial infectivity and survival within macrophages and modulates host pro‐inflammatory response via inhibition of phagolysosomal fusion

DNA methylation is an important epigenetic mechanism that impacts gene expression and helps the mycobacteria to survive inside the host in different microenvironments. About 3% of the genome of Mycobacterium tuberculosis , the tuberculosis (TB) causing bacteria, codes for methyl transferases, many of which are believedto play major role in modulating host‐bacterial pathogenesis. A hypothetical gene coding for a DNA methyl transferase, unique to mycobacterium tuberculosis complex was identified, cloned and transformed into Mycobacterium smegmatis in order to understand the characteristics and function of this gene. Expression of this methyltransferase in M. smegmatis caused growth retardation and morphological changes . In addition, recombinant M. smegmatis showed increased infectivity and intracellular survival in human macrophage cell line by escaping the phagolysosomal maturation. Infection of macrophages with recombinant M. smegmatis was associated with significant necrosis and increased levels of LDH as compared to controls, promoting higher dissemination of bacteria. Surprisingly it also plays role in forming granuloma‐like structures in infected macrophages. Furthermore, macrophages infected with recombinant M. smegmatis showed a significant reduction in the secretion of bactericidal factors such as nitric oxide and major inflammatory cytokines. Co‐culture of infected THP1 cells and T cells induced strong cell mediated immune response by releasing high levels of IFN‐γ and IL‐2, promoting T cell activation and expansion. These findings point to an important role of this DNA methyl transferase in mediating survival of mycobacteria within host cells and regulating pathogenesis.