Slow growth of Mycobacterium tuberculosis at acidic pH is regulated by phoPR and host‐associated carbon sources

Abstract

Summary During pathogenesis, Mycobacterium tuberculosis (Mtb) colonizes environments, such as the macrophage or necrotic granuloma, that are acidic and rich in cholesterol and fatty acids. The goal of this study was to examine how acidic pH and available carbon sources interact to regulate Mtb physiology. Here we report that Mtb growth at acidic pH requires host-associated carbon sources that function at the intersection of glycolysis and the TCA cycle, such as pyruvate, acetate, oxaloacetate and cholesterol. In contrast, in other tested carbon sources, Mtb fully arrests its growth at acidic pH and establishes a state of non-replicating persistence. Growth-arrested Mtb is resuscitated by the addition of pyruvate suggesting that growth arrest is due to a pH-dependent checkpoint on metabolism. Additionally, we demonstrate that the phoPR two-component regulatory system is required to slow Mtb growth at acidic pH and functions to maintain redox homeostasis. Transcriptional profiling and functional metabolic studies demonstrate that signals from acidic pH and carbon source are integrated to remodel pathways associated with anaplerotic central metabolism, lipid anabolism and the regeneration of oxidized cofactors. Because phoPR is required for Mtb virulence in animals, we suggest that pH-driven adaptation may be critical to Mtb pathogenesis.

EspR, a regulator of the ESX-1 secretion system in Mycobacterium tuberculosis, is directly regulated by the two-component systems MprAB and PhoPR

“…Although mutations in this region disrupted binding of these response regulators in EMSAs, we did not detect a corresponding effect on expression of espR in recombinant strains carrying the same mutations. However, both PhoPR and MprAB are stress-responsive TCSs (Baker et al, 2014;He et al, 2006; and it is possible that these regulatory sites are utilized under conditions not tested in our study. Mutations in MprA Region-2, however, were associated with reduced expression of espR and EspR-target genes.…”

“…Rv2745c (ClgR) is a regulator associated with the responses to redox stress, DNA damage and recovery from hypoxia (McGillivray et al, 2014;Sherrid et al, 2010;Wang et al, 2011). As PhoPR is involved in the maintenance of redox homeostasis (Baker et al, 2014), it is possible that Rv2745c is part of the PhoPR regulon as well as the MprAB/ SigE and EspR regulons.…”

Rv3852 (H-NS) of Mycobacterium tuberculosis Is Not Involved in Nucleoid Compaction and Virulence Regulation

“…As PhoPR is required to slow growth at acidic pH (26), the ΔphoP strain (27) was used as a control. At neutral pH, the ΔphoP mutant showed a slight growth defect (Fig.…”

Interplay of human macrophages and Mycobacterium tuberculosis phenotypes

“…This could originate from ongoing bacterial replication at the time of infection that is not slowed upon delivery to acidic phagolysosomes and by lysosomal effectors within the first day yet, but later during the course of infection, reflecting that Mtb needs time to adapt to host pressures. Mtb is well equipped to withstand acidic conditions and hence slows its replication [247][248][249] as reflected in Paper 1, Figure 1A.…”

“…Being capable of tolerating acidic stress that is lethal for many other microbial pathogens, Mtb possesses a membrane protein maintaining neutral intracellular pH in an acidic environment [247], and a pH-responsive locus, aprABC, present exclusively in the Mtb complex strains. aprABC expression is regulated by the phoP two component regulatory system that -in an acidic environment -slows Mtb growth, stops growth when certain carbon sources are missing, and induces genes for lipid metabolism [248,249]. Therefore, the acidic environment per se does not affect Mtb viability, but rather prepares the bacterium to adapt to intracellular challenges, and phagolysosomal effector functions such as hydrolytic enzymes are in many cases dependent on acidic pH.…”