title: Role of Salmonella enterica serovar Typhimurium two-component system PreA/PreB in modulating PmrA-regulated gene transcription.
abstract: The PmrA/PmrB two-component system encoded by the pmrCAB operon regulates the modification of Salmonella enterica serovar Typhimurium lipopolysaccharide leading to polymyxin B resistance. PmrA and PhoP are the only known activators of pmrCAB. A transposon mutagenesis screen for additional regulators of a pmrC::MudJ fusion led to the identification of a two-component system, termed PreA/PreB (pmrCAB regulators A and B), that controls the transcription of the pmrCAB operon in response to unknown signals. The initial observations indicated that insertions in, or a deletion of, the preB sensor, but not the preA response regulator, caused upregulation of pmrCAB. Interestingly, the expression of pmrCAB was not upregulated in a preAB mutant grown in LB broth, implicating PreA in the increased expression of pmrCAB in the preB strain. This was confirmed by overexpression of preA(+) in preAB or preB backgrounds, which resulted in significant upregulation or further upregulation of pmrCAB. No such effect was observed in any tested preB(+) backgrounds. Additionally, an ectopic construct expressing a preA[D51A] allele also failed to upregulate pmrC in any of the pre backgrounds tested, which implies that there is a need for phosphorylation in the activation of the target genes. The observed upregulation of pmrCAB occurred independently of the response regulators PmrA and PhoP. Although a preB mutation led to increased transcription of pmrCAB, this did not result in a measurable effect on polymyxin B resistance. Our genetic data support a model of regulation whereby, in response to unknown signals, the PreB sensor activates PreA, which in turn indirectly upregulates pmrCAB transcription.
authors.affiliation: Department of Molecular Virology, Immunology, and Medical Genetics and Center for Microbial Interface Biology, The Ohio State University, 270 TMRF, 420 W. 12th Avenue, Columbus, OH 43210, USA.
authors.forename: Massimo
authors.initials: M
authors.lastname: Merighi
authors.forename: Amanda
authors.initials: A
authors.lastname: Carroll-Portillo
authors.forename: Alecia N
authors.initials: AN
authors.lastname: Septer
authors.forename: Aditi
authors.initials: A
authors.lastname: Bhatiya
authors.forename: John S
authors.initials: JS
authors.lastname: Gunn
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004251:DNA Transposable Elements; D015964:Gene Expression Regulation, Bacterial; D008826:Microbial Sensitivity Tests; D016254:Mutagenesis, Insertional; D009876:Operon; D011112:Polymyxin B / Q000494:pharmacology; D012486:Salmonella typhimurium / Q000187:drug effects / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D015398:Signal Transduction; D014158:Transcription, Genetic
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004251:DNA Transposable Elements; C081902:pmrA protein, Bacteria; D011112:Polymyxin B