Intracellular compartmentalization shapes lipid access and metabolic fitness of mycobacteria

Intracellular mycobacteria encounter distinct metabolic environments as they transition between vacuolar and cytosolic compartments within host cells, yet how nutrient access is shaped by this compartmentalization remains poorly understood. Here, we use Mycobacterium marinum fatty acyl- CoA ligase 6 (FACL6) as a functional entry point to examine how lipid acquisition and processing are coordinated during intracellular infection. By combining host and bacterial genetic perturbations with dual RNA-sequencing and high-resolution imaging in genetically tractable amoebal infection models, and validating key phenotypes in mammalian cells, we show that lipid metabolic programs in intracellular mycobacteria are tightly linked to subcellular localization. Sterol utilization and neutral lipid storage are preferentially engaged during the intravacuolar phase, whereas cytosolic exposure is associated with reduced lipid accumulation. Deletion of facl6 disrupts this coordinated scenario, resulting in altered bacterial cell envelope architecture, premature membrane damage, defective neutral lipid storage, and reduced intracellular fitness despite enhanced cytosolic access. Together, these findings reveal that loss of FACL6 causes intrinsic defects in lipid handling and highlight how compartment-specific lipid environments shape the outcome of mycobacterial infection. TeaserLoss of FACL6 reveals how intracellular compartmentalization shapes mycobacterial lipid metabolism