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

The human pathogen Mycobacterium tuberculosis (Mtb) thrives in lipid-rich microenvironments. Long-chain fatty acids (LCFA) are some of the most abundant lipids encountered by Mtb during infection. Mtb has evolved to utilize LCFA as a preferred carbon source, however, LCFA are also known to be potent antimicrobials. Mtb must therefore employ mechanisms to utilize LCFA as a carbon source while avoiding its bactericidal properties. We used transposon sequencing (TnSeq) to define a Mtb LCFA resistome, and found it to be composed by 38 genes. Surprisingly, Mtb requires a diverse set of metabolic pathways to avoid LCFA toxicity, indicating pleiotropic effects of LCFA in Mtb metabolism. As a functional follow-up on the TnSeq screen, we investigated the function of the universal stress protein TB15.3 in LCFA metabolism and during infection. We show that TB15.3 acts as a "metabolic break" for LCFA uptake and catabolism, avoiding deleterious membrane hyperpolarization. This was associated with loss of viability in the chronic phase of infection in mice and in an in vitro caseum model. Our work highlights Mtb LCFA resistance mechanisms as an important adaptation to the host and a promising target space to be exploited for drug development.