title: Phosphate starvation: a novel signal that triggers ESX-5 secretion in Mycobacterium tuberculosis.
abstract: Mycobacterium tuberculosis uses the Type VII ESX secretion systems to transport proteins across its complex cell wall. ESX-5 has been implicated in M. tuberculosis virulence, but the regulatory mechanisms controlling ESX-5 secretion were unknown. Here we uncover a link between ESX-5 and the Pst/SenX3-RegX3 system that controls gene expression in response to phosphate availability. The DNA-binding response regulator RegX3 is normally activated by phosphate limitation. Deletion of pstA1, which encodes a Pst phosphate uptake system component, causes constitutive activation of RegX3. A ΔpstA1 mutant exhibited RegX3-dependent overexpression of esx-5 genes and hyper-secretion of the ESX-5 substrates EsxN and PPE41 when the bacteria were grown in phosphate-rich medium. In wild-type M. tuberculosis, phosphate limitation activated esx-5 transcription and secretion of both EsxN and PPE41, and this response required RegX3. Electrophoretic mobility shift assays revealed that RegX3 binds directly to a promoter within the esx-5 locus. Remarkably, phosphate limitation also induced secretion of EsxB, an effector of the virulence-associated ESX-1 secretion system, though this induction was RegX3 independent. Our work demonstrates that the Pst/SenX3-RegX3 system directly regulates ESX-5 secretion at the transcriptional level in response to phosphate availability and defines phosphate limitation as an environmental signal that activates ESX-5 secretion.
authors.affiliation: Department of Microbiology and Immunology, Minneapolis, MN, 55455, USA.
authors.forename: Sarah R
authors.initials: SR
authors.lastname: Elliott
authors.affiliation: Department of Microbiology and Immunology, Minneapolis, MN, 55455, USA.|Center for Infectious Diseases and Microbiology Translational Research, University of Minnesota Twin Cities, Minneapolis, MN, 55455, USA.
authors.forename: Anna D
authors.initials: AD
authors.lastname: Tischler
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites / Q000235:genetics; D024202:Electrophoretic Mobility Shift Assay; D004789:Enzyme Activation / Q000502:physiology; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics; D009169:Mycobacterium tuberculosis / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity; D010710:Phosphates / Q000378:metabolism*; D010770:Phosphotransferases / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding / Q000502:physiology; D000069377:Type VII Secretion Systems / Q000235:genetics / Q000378:metabolism*; D037521:Virulence Factors / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism
chemical_list: D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; C000621160:ESX-5 protein, Mycobacterium tuberculosis; D010710:Phosphates; C110608:RegX3 protein, Mycobacterium; D000069377:Type VII Secretion Systems; D037521:Virulence Factors; C078408:phosphate-specific transport protein A, bacteria; D010770:Phosphotransferases; C110607:SenX3 protein, Mycobacterium