Deficiency of the Mycobacterial Lipoarabinomannan Biosynthesis Glycosyltransferase MptC Enhances Antibacterial Immune Response and Rifapicin Antibiotic Susceptibility.

The mycobacterial complex cell envelope serves as a formidable barrier against host immunity and antibiotics. Lipomannan (LM) and lipoarabinomannan (LAM) are key structural components of the mycobacterial envelope and potent immunomodulators. The mycobacterial lipoarabinomannan biosynthesis mannosyltransferase MptC modifies the multiple α-(1→2)-linked branched mannan residues of LAM in the mycobacteria. However, the role of MptC in mycobacterial infectivity, antibiotic susceptibility and host immune regulation remains poorly understood. An mptC (also named MSMEG_4247) knockout Mycobacterium smegmatis mc2-155 (M. smeg) strain (designated as M. smegΔmptC) was generated using CRISPR-Cas12a technology. The effects of MptC on bacterial physiology, cell wall permeability, drug sensitivity, immune cell function, and survival during infection are analyzed through glycogen staining, drug sensitivity tests, and cellular and mouse infection models. MptC deficiency results in a loss of LM and increase in LAM synthesis. The M. smegΔmptC mutant strain exhibits enhanced cell wall permeability and reduces hydrophobicity. Functionally, the mptC knockout strain increases the intracellular cytokines (IFN-γ, TNF-a and IL-17) production of T cells in mice. Consequently, results based on both macrophage and mouse infection models demonstrate that the M. smegΔmptC strain has less bacterial loads and higher susceptibility to antibiotic rifampicin. Mannosyltransferase MptC plays an important role in maintaining cell wall integrity (via LM/LAM synthesis), regulating T cell responses, and influencing antibiotic susceptibility in mycobacteria.