Abstract
Inorganic polyphosphate (poly P) has been postulated to play a regulatory role in the transition to bacterial persistence. In bacteria, poly P balance in the cell is maintained by the hydrolysis activity of the exopolyphosphatase PPX. However, the Mycobacterium tuberculosis PPX has not been characterized previously. Here we show that recombinant MT0516 hydrolyzes poly P, and an MT0516-deficient M. tuberculosis mutant exhibits elevated intracellular levels of poly P and increased expression of the genes mprB, sigE, and rel relative to the isogenic wild-type strain, indicating poly P-mediated signaling. Deficiency of MT0516 resulted in decelerated growth during logarithmic-phase in axenic cultures, and tolerance to the cell wall-active drug isoniazid. The MT0516-deficient mutant showed a significant survival defect in activated human macrophages and reduced persistence in the lungs of guinea pigs. We conclude that exopolyphosphatase is required for long-term survival of M. tuberculosis in necrotic lung lesions.
Highlights
It is estimated that 2 billion people worldwide have latent tuberculosis (TB) infection, representing a vast potential reservoir for subsequent reactivation disease, in the setting of the HIV pandemic [1]
During the Escherichia coli stringent response, intracellular poly P levels increase significantly as a result of inhibition of PPX activity by the alarmone (p)ppGpp [14], which is synthesized by Rel when uncharged tRNA binds nonenzymatically to the acceptor site of an elongating ribosome stalled at a codon on an mRNA, signaling that the environment is limited in amino acids [15]
Supporting a potential role for poly P as a growth regulatory molecule in M. tuberculosis (Mtb), recent studies found that that the expression of Rv2984, encoding the poly P kinase PPK1, is induced during stationary phase [19] and inorganic phosphate starvation [40]. We have identified another mechanism for Mtb regulation of intrabacillary poly P levels through expression of Rv0496/MT0516, which encodes a PPX responsible for poly P hydrolysis
Summary
It is estimated that 2 billion people worldwide have latent tuberculosis (TB) infection, representing a vast potential reservoir for subsequent reactivation disease, in the setting of the HIV pandemic [1]. Latent TB infection is believed to result from the immunological control of a small number of nonreplicating and slowly metabolizing organisms [2], which have adapted to the unfavorable microenvironmental conditions within lung granulomas [3], likely including hypoxia [4], nutrient limitation, and acidic pH [5]. These ‘‘dormant’’ bacilli exhibit phenotypic tolerance to bactericidal antibiotics such as isoniazid [6], which inhibits the mycolic acid synthesis pathway required for cell wall synthesis [7,8]. P induces expression of the rpoS gene [16,17], which is regulated by (p)ppGpp, and the encoded RNA polymerase sigma factor RpoS directs the transcription of .50 genes involved in cascades downshifting growth and metabolism, thereby adjusting the cell to a persistent state [18]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
