Differential formation of nitrate-responsive mycobacterial intracytoplasmic membranes during Mycobacterium tuberculosis infection.

Subcellular compartmentalization of metabolic processes is a main feature of prokaryotic and eukaryotic architecture. Environmental bacteria generate intracytoplasmic membranes (ICMs) as a crucial strategy to adapt their metabolism to environmental changes. While pathogenic intracellular bacteria also perceive various stressful stimuli during host interactions, the subsequent re-organization of their internal architecture has not been explored. Using cryo-electron tomography, we show that Mycobacterium tuberculosis (Mtb), a major human pathogen, is able to form ICMs outside and inside host cells in a strain-dependent manner. We characterize these Mycobacterial intracytoplasmic Membranes (MIMs) as nitrate-induced structures. Furthermore, we uncover that MIM formation in Mtb during macrophage infection correlates with limited cellular inflammatory responses. Our findings reveal a cytoplasmic structure in Mtb and link it to a functional mechanism that enables the bacterium to adapt to its intracellular niche.