A highly conserved two-gene operon is crucial for lipoarabinomannan localization, pathogenesis, and cell envelope function in Mycobacterium abscessus

Abstract

Mycobacterium abscessus is an emerging threat, causing infections that are difficult to treat due to intrinsic resistance to most antibiotics. Determinants of M. abscessus physiology and pathogenesis remain poorly understood, hampering therapeutic development. Here, we show that in M. abscessus, the lprg-mfs operon is essential for virulence in macrophages and in mice. Loss of lprg-mfs in M. abscessus causes accumulation of the glycolipid lipoarabinomannan (LAM) on the cell surface and in culture supernatant suggesting that this system participates in LAM import. This contrasts with its proposed role in M. tuberculosis where lprg-mfs has been implicated in the export of various lipids. Consistent with altered lipid distribution, the lprg-mfs mutant displays severe defects in mycomembrane permeability, fluidity, and integrity, and expression of mfs alone restores only a subset of these phenotypes, revealing a surprising uncoupling of envelope fluidity and permeability. Using a suppressor screen to further investigate factors that control the distribution of lipoarabinomannan we find that a point mutation in the unannotated gene MAB_0995 can fully or partially complement all deletion mutant phenotypes. Our data also show that lipoarabinomannan in the mycomembrane is dynamically regulated in response to environmental conditions, including hypoxia and macrophage infection. Together, these findings redefine the role of LprG/Mfs in mycobacterial cell envelope homeostasis and reveal unexpected plasticity in mycomembrane lipid regulation in M. abscessus. ImportanceThe emerging pathogen Mycobacterium abscessus causes life-threatening lung infections in certain patients that are extremely difficult to treat due to its intrinsic resistance to most antibiotics. However, the process by which this organism establishes infection is poorly understood, as are the specific determinants of antibiotic tolerance. Better knowledge of the genes required for virulence and impermeability to antibiotics in M. abscessus could enable to development of more effective treatments. The significance of this study is the demonstration that the lprg-mfs operon is required both for pathogenesis and for impermeability in M. abscessus. Further, our study shows a correlation between cell envelope characteristics and the distribution of the molecule lipoarabinomannan, suggesting a specific mechanism by which these crucial characteristics are mediated.