Role of Salmonella enterica serovar Typhimurium two-component system PreA/PreB in modulating PmrA-regulated gene transcription.
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.
Merighi
Massimo
M
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.
Carroll-Portillo
Amanda
A
Septer
Alecia N
AN
Bhatiya
Aditi
A
Gunn
John S
JS
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
D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004251:DNA Transposable Elements; C081902:pmrA protein, Bacteria; D011112:Polymyxin B