Unravelling the protective effects: PknJ modulates MmaA4 expression and rifampicin susceptibility in Mycobacterium bovis BCG.

Mycobacterium tuberculosis establishes long-term persistence within the host, requiring a better understanding of the molecular processes controlling intracellular survival by altering immunological responses. The adaptability and persistence of mycobacteria are strongly influenced by post-translational modifications, particularly phosphorylation and methylation. This study examined the role of serine/threonine kinase PknJ in regulating slow growth and intracellular survival of Mycobacterium bovis BCG through its association with Rv0642c (MmaA4), a key mycolic acid methyltransferase. Deletion of pknJ led to a significant reduction in mmaA4 expression and methyltransferase activity during extracellular growth, whereas both parameters were enhanced during intracellular growth within murine macrophages. The pknJ mutant also exhibited increased sensitivity to rifampicin under extracellular conditions, accompanied by increased nitric oxide production in infected macrophages and an altered tolerance to acidic stress. Collectively, the present findings highlight a PknJ-MmaA4 regulatory axis in an avirulent mycobacterial model. This axis appears to integrate cell-wall remodelling, stress adaptation, and intracellular persistence of mycobacteria.