PecS regulates the urate-responsive expression of type 1 fimbriae in klebsiella pneumoniae CG43

In the Klebsiella pneumoniae CG43 genome, the divergently transcribed genes coding for PecS, the MarR-type transcription factor, and PecM, the drug metabolite transporter, are located between the type 1 and type 3 fimbrial gene clusters. The intergenic sequence pecO between pecS and pecM contains three putative PecS binding sites and a CpxR box. Electrophoretic mobility shift assay revealed that the recombinant PecS and CpxR could specifically bind to the pecO sequence, and the specific interaction of PecS and pecO could be attenuated by urate. The expression of pecS and pecM was negatively regulated by CpxAR and PecS, and was inducible by exogenous urate in the absence of cpxAR. Compared with CG43S3DcpxAR, the derived mutants CG43S3DcpxARDpecS and CG43S3DcpxARDpecSDpecM exerted similar levels of sensitivity to H₂O₂ or paraquat, but higher levels of mannose-sensitive yeast agglutination activity and FimA production. The promoter activity and transcript levels of fimA in CG43S3DcpxAR were also increased by deleting pecS. However, no binding activity between PecS and the fimA promoter could be observed. Nevertheless, PecS deletion could reduce the expression of the global regulator HNS and release the negative effect of HNS on FimA expression. In CG43S3DcpxAR, the expression of FimA as well as PecS was inducible by urate, whilst urate-induced FimA expression was inhibited by the deletion of pecS. Taken together, we propose that K. pneumoniae PecS indirectly and negatively regulates the expression of type 1 fimbriae, and the regulation is urateinducible in the absence of CpxAR.