FucR Functions as a Transcriptional Regulator for L-Fucose Utilization in Campylobacter jejuni

<i>Campylobacter jejuni</i> is an enteric pathogen and a major cause of foodborne illness worldwide. It has been shown that <i>C. jejuni</i> primarily utilizes amino acids as its preferred energy source, but its ability to utilize L-fucose can grant a competitive advantage during intestinal colonization. In <i>C. jejuni</i>, fucose utilization is encoded by a variable region named plasticity region 2 (PR2); however, the regulatory mechanism for the region remains unknown and is investigated in this study. Genomic sequence analysis revealed that immediately upstream of the fucose utilization operon is a putative IclR-type transcriptional regulator, <i>cj0480c</i> (named <i>fucR</i> here). To determine whether <i>fucR</i> regulates the expression of the fucose utilization operon, we generated a knock-out mutant of <i>fucR</i>. RT-PCR and microarray analysis found that all the genes in the operon were polycistronic and significantly upregulated in the <i>fucR</i> mutant compared with their expression in the wild-type strain. In the presence of fucose, expression of the fucose utilization genes was induced in the wild-type strain but no longer inducible in the <i>fucR</i> mutant, suggesting that FucR functions as a repressor for the fucose utilization operon. To determine whether FucR directly or indirectly regulates the fucose utilization operon, a 6xHis-tagged full-length FucR was produced in <i>Escherichia coli</i>, and the purified recombinant FucR was used in electrophoretic mobility shift assay, which demonstrated that FucR bound specifically to the promoter region of the fucose utilization operon. Together, these results indicate that the L-fucose utilization operon in <i>C. jejuni</i> is directly regulated by FucR, which functions as a transcriptional repressor and modulates the expression of the operon in response to fucose.