Mycobacterium tuberculosis long-chain fatty acid resistome reveals universal stress protein TB15.3 as essential for infection

The human pathogen Mycobacterium tuberculosis (Mtb) thrives in lipid-rich microenvironments. A strong body of evidence demonstrated that, during infection, Mtb utilizes long-chain fatty acids (LCFA) as a preferred carbon source. However, LCFA also have antimicrobial properties. Mtb must therefore employ mechanisms to utilize LCFA while mitigating their toxicity. Using transposon sequencing (TnSeq), we defined the Mtb LCFA resistome as comprising 38 genes. Surprisingly, LCFA resistance requires diverse metabolic pathways, indicating pleiotropic effects of LCFA on Mtb physiology. We investigated the function of the TnSeq top-hit, the universal stress protein TB15.3, and demonstrate that it participates in a "metabolic brake" mechanism restricting LCFA uptake and catabolism to prevent membrane hyperpolarization. TB15.3 absence caused Mtb to lose viability during chronic infection in mice and in an in vitro caseum model. Our work highlights Mtb LCFA resistance mechanisms as an important host adaptation and a promising target space for drug development.