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Positive regulation of flhDC expression by OmpR in Yersinia pseudotuberculosis

¹ State Key Laboratory of Virology, Wuhan Institute of Virology, the Chinese Academy of Sciences, Wuhan 430071, China
² Institute of Infection, Immunity and Inflammation, Centre for Biomolecular Sciences, University of Nottingham, Nottingham NG7 2UH, UK
³ Graduate School of the Chinese Academy of Sciences, Beijing 100049, China

OmpR has been demonstrated to negatively regulate the expression of the flagellar master operon flhDC in a wide variety of bacterial species. Here we report the positive regulation of flhDC expression by OmpR in Yersinia pseudotuberculosis. A ⁷⁰-dependent promoter was identified by primer extension analysis and an active region with two conserved OmpR-binding sites around the flhDC promoter was confirmed. To confirm the regulation of flhDC expression by OmpR, flhDC as well as the downstream flagellar genes fliA, flgD, flgA, flgM, fliC and flaA were fused to lacZ, and decreased expression of all these genes in an ompR mutant (ompR) was detected. Furthermore, ompR was defective in bacterial motility and flagella synthesis. This defect was due to the low level of expression of flhDC in ompR since overproduction of FlhDC in ompR restored bacterial motility. The importance of two conserved OmpR-binding sites around the flhDC promoter region in the regulation of flhDC expression by OmpR was demonstrated by the fact that mutation of either one or both sites significantly decreased the promoter activity in the wild-type but not in ompR. The binding of OmpR to these two sites was also demonstrated by DNA mobility shift assay. The possible mechanism underlying this positive regulation in Y. pseudotuberculosis is discussed. To our knowledge, this is the first report to demonstrate that OmpR positively regulates flhDC expression.

Correspondence
Shiyun Chen
sychen{at}wh.iov.cn

A supplementary table of primers used in this study and a supplementary figure showing the sequence alignment of OmpR from different bacterial species are available with the online version of this paper.