Mycobacterium tuberculosis overcomes phosphate starvation by extensively remodelling its lipidome with phosphorus-free lipids

Abstract

Tuberculosis (TB) is the biggest cause of death from infectious disease worldwide [1-4]. The causative agent, Mycobacterium tuberculosis (Mtb), possesses a complex cell envelope that determines many of the key physiologic and virulence properties that facilitate infection, which comprises multiple classes of unique lipids [5-7]. The macrophage phagosome is a key reservoir of infection in pulmonary TB and multiple studies have shown that inorganic phosphate (Pi) is limiting in this environment [8-11]. The ability of Mtb to sense and respond to phosphate starvation is required for virulence in animal models and replication in human macrophages in vitro [12-14]. Here, we show that during Pi restriction the Mtb lipidome is markedly remodelled such that phospholipids are replaced with multiple classes of phosphorus-free lipids, some of which have not been documented before. Further, we discover that Mtb can metabolise phospholipid polar heads derived from host pulmonary surfactant as an alternative phosphate source, which sustains cell division for several generations during Pi restriction. These dual manipulations of phospholipid metabolism provide Mtb with an escape from phosphate restriction specific to the infection of alveolar macrophages, one of the earliest steps in establishing pulmonary tuberculosis. The changes in envelope lipidome remodelling, akin to that observed in some marine and terrestrial bacteria [15-20] suggests that standard Mtb culture conditions that use media with high concentrations of Pi do not reflect the physiologic environment during infection, thereby potentially undermining vaccine and drug development for tuberculosis. Moreover, the distinct Mtb phosphate-free lipids and the metabolic pathways that generate them could provide new antibiotic targets.