Analysis of putative chemoreceptor proteins of Campylobacter jejuni

Campylobacter jejuni is the primary food borne bacterial pathogen in the developed world. A very important reservoir for C. jejuni is the gut of chickens, which are colonized efficiently and commensally by this organism. Predominantly the mucus filled crypts of the lower gastrointestinal tract are found to be colonized by C. jejuni and the bacteria are expected to be attracted to this environment by chemotaxis. In order to explore the role of chemotaxis in C. jejuni colonization and to identify chemoreceptors with matching attractants and/or repellants we have constructed deletion mutants of five putative chemoreceptors (tlp1, tlp2, tlp3, docB and docC) in the sequenced strain C. jejuni NCTC11168. The chemotactic capacity of these mutants were investigated by quantifying bacterial accumulation in capillaries filled with attractants or repellants and by measuring migration zones towards or away from substances dispensed in filter discs on PBS softagar. Interestingly, strong attractions towards substances with low pH were observed repeatedly in the filter assay but not in the capillary assay. However, there were no striking chemotactic difference between the mutants and the parental strain, hence indicating the chemoreceptors of C. jejuni to have overlapping sensing capacities. To facilitate independent investigation of the chemoreceptors are we now in the process of analyzing all 10 putative chemoreceptors of C. jejuni individually in an E. coli background. Furthermore, the five C. jejuni mutants are being analyzed in adherence and invasion assays with both human and chicken cells to explore the possibility that these membrane spanning proteins interact with host cells rather than operating as chemoreceptors.