Diversity and function of the lipooligosaccharide biosynthesis genes from Campylobacter jejuni

The enteric pathogen, Campylobacter jejuni, produces a range of LOS structures, however, the precise functions of LOS molecules in infection are largely undetermined. LOS structural diversity is known to arise from variation in LOS biosynthesis gene content and gene sequence. In determining the extent of LOS biosynthesis gene content variation in a group of mainly clinical C. jejuni isolates, in this study two new clusters of LOS biosynthesis genes have been identified. The C. jejuni LOS core can also undergo phase variation due to the presence of GC homopolymeric tracts in the protein coding sequence of biosynthesis genes in the cluster. Therefore, the variation in homopolymeric tract length was investigated in five genes including those in the LOS biosynthesis cluster. Many bacteria are known to vary LPS or LOS structure in response to different environment stimuli. Following the identification of a number of promoters in the LOS core biosynthesis cluster, promoter activity was measured following growth under several different conditions. Although promoter expression did not vary extensively with the different environmental stimuli, less LOS was extracted from cell grown under iron-limitation. The other aim of this work was to investigate LOS biosynthesis gene function. The genes waaF and lpxL are involved in core and lipid A biosynthesis respectively. Mutation of both genes had a substantial effect on LOS core structure and preliminary studies indicate both genes are important for adhesion and invasion of human intestinal cells. The deletion of several genes from the general protein glycosylation pathway also led to the truncation of the LOS core, indicating overlap between the two carbohydrate biosynthesis pathways.