CmeR functions as global regulator in Campylobacter jejuni

In Campylobacter jejuni CmeR functions as a transcriptional repressor modulating the expression of the multidrug efflux pump CmeABC, which plays an important role in the resistance to antimicrobial agents and bile compounds. Using DNA microarray, we identified multiple genes that are either activated or repressed by CmeR in C. jejuni. The DNA microarray data was independently confirmed by quantitative real-time RT-PCR. The CmeR-regulated genes encode products of diverse functions including membrane proteins, drug efflux transporters, the C4-dicarboxylate transport/utilization system, and enzymes involved in the biosynthesis of capsular polysaccharide (CPS). Immunoblotting and Alcian blue staining further showed that CPS production is reduced in the cmeR mutant, confirming the regulation of CPS production by CmeR. Electrophoretic mobility shift assay revealed that recombinant CmeR bound specifically to several intergenic regions in the CPS gene cluster, suggesting that CmeR directly regulates this gene cluster. In the chicken host, the mutant carrying a null mutation in cmeR was severely outcompeted by the isogenic wild-type strain. Together these data indicate that CmeR functions as a global regulator in C. jejuni, modulates the expression of genes encoding diverse functions, and is important for the fitness of Campylobacter in the intestinal tract. Keywords: cell type comparison To compare the transcriptomes of the CmeR mutant and NCTC11168, equal volumes of Cy3- or Cy5-labeled cDNAs from the wild-type or cmeR mutant strain were combined and then hybridized to the microarray slides. A second microarray slide was hybridized with the dyes reversed to the two samples to normalize for dye bias. The hybridization experiment was repeated three times by using total RNA isolated from three independent experiments. Thus, six technical replicates from three biologically independent experiments were used for data analysis.