Investigating the Role of FlhF Identifies Novel Interactions With Genes Involved in Flagellar Synthesis in Campylobacter jejuni

Abstract

FlhF is a key protein required for complete flagellar synthesis, and its deletion results in the complete absence of a flagella and thus motility in <i>Campylobacter jejuni</i>. However, the specific mechanism still remains unknown. In this study, RNA-Seq, EMSAs, ChIP-qPCR and β-Galactosidase assays were performed to elucidate the novel interactions between FlhF and genes involved in flagellar synthesis. Results showed that FlhF has an overall influence on the transcription of flagellar genes with an <i>flhF</i> mutant displaying down-regulation of most flagellar related genes. FlhF can directly bind to the <i>flgI</i> promoter to regulate its expression, which has significant expression change in an <i>flhF</i> mutant. The possible binding site of FlhF to the <i>flgI</i> promoter was explored by continuously narrowing the <i>flgI</i> promoter region and performing further point mutations. Meanwhile, FlhF can directly bind to the promoters of <i>rpoD</i>, <i>flgS</i>, and <i>fliA</i> encoding early flagellin regulators, thereby directly or indirectly regulating the synthesis of class I, II, and III flagellar genes, respectively. Collectively, this study demonstrates that FlhF may directly regulate the transcription of flagellar genes by binding to their promoters as a transcriptional regulator, which will be helpful in understanding the mechanism of FlhF in flagellar biosynthetic and bacterial flagellation in general.