Inorganic polyphosphate accumulation suppresses the dormancy response and virulence in Mycobacterium tuberculosis

Abstract

Stringent response pathways involving inorganic polyphosphate (PolyP) play an essential role in bacterial stress adaptation and virulence. The intracellular levels of PolyP are modulated by the activities of polyphosphate kinase-1 (PPK1), polyphosphate kinase-2 (PPK2), and exopolyphosphatases (PPXs). The genome of <i>Mycobacterium tuberculosis</i> encodes two functional PPXs, and simultaneous deletion of <i>ppx1</i> and <i>ppx2</i> results in a defect in biofilm formation. We demonstrate here that these PPXs cumulatively contribute to the ability of <i>M. tuberculosis</i> to survive in nutrient-limiting, low-oxygen growth conditions and also in macrophages. Characterization of single (Δ<i>ppx2</i>) and double knockout (<i>dkppx</i>) strains of <i>M. tuberculosis</i> indicated that PPX-mediated PolyP degradation is essential for establishing bacterial infection in guinea pigs. RNA-Seq-based transcriptional profiling revealed that relative to the parental strain, the expression levels of DosR regulon-regulated dormancy genes were significantly reduced in the <i>dkppx</i> mutant strain. In concordance, we also provide evidence that PolyP inhibits the autophosphorylation activities associated with DosT and DosS sensor kinases. The results in this study uncover that enzymes involved in PolyP homeostasis play a critical role in <i>M. tuberculosis</i> physiology and virulence and are attractive targets for developing more effective therapeutic interventions.