YjjQ Represses Transcription of flhDC and Additional Loci in Escherichia coli

The presumptive transcriptional regulator YjjQ has been identified as being virulence associated in avian pathogenicEscherichia coli (APEC). In this work, we characterize YjjQ as transcriptional repressor of theflhDC operon, encoding the master regulator of flagellar synthesis, and of additional loci. The latter includegfc (capsule 4 synthesis),ompC (outer membrane porin C),yfiRNB (regulated c-di-GMP synthesis), and loci of poorly defined function (ybhL andymiA-yciX ). We identify the YjjQ DNA-binding sites at theflhDC andgfc promoters and characterize a DNA-binding sequence motif present at all promoters found to be repressed by YjjQ. At theflhDC promoter, the YjjQ DNA-binding site overlaps the RcsA-RcsB DNA-binding site. RcsA-RcsB likewise represses theflhDC promoter, but the repression by YjjQ and that by RcsA-RcsB are independent of each other. These data suggest that YjjQ is an additional regulator involved in the complex control offlhDC at the level of transcription initiation. Furthermore, we show that YjjQ represses motility of theE. coli K-12 laboratory strain and of uropathogenicE. coli (UPEC) strains CFT073 and 536. Regulation offlhDC ,yfiRNB , and additional loci by YjjQ may be features relevant for pathogenicity.IMPORTANCE Escherichia coli is a commensal and pathogenic bacterium causing intra- and extraintestinal infections in humans and farm animals. The pathogenicity ofE. coli strains is determined by their particular genome content, which includes essential and associated virulence factors that control the cellular physiology in the host environment. However, the gene pools of commensal and pathogenicE. coli are not clearly differentiated, and the function of virulence-associated loci needs to be characterized. In this study, we characterize the function ofyjjQ , encoding a transcription regulator that was identified as being virulence associated in avian pathogenicE. coli (APEC). We characterize YjjQ as transcriptional repressor of flagellar motility and of additional loci related to pathogenicity.