Characterisation of the lipooligosaccharide biosynthesis gene cluster in Campylobacter species

The extensive genetic variation in the lipooligosaccharide (LOS) core biosynthesis gene cluster, a majority of which occurs in the LOS outer core biosynthesis gene content present between lgtF and waaV, have led to the development of a classification system; with 8 classes (I-VIII) for Campylobacter coli (C. coli) LOS region and four groups (1-4) with 23 classes (A-W) for Campylobacter jejuni (C. jejuni) LOS region. The aim of this work was to characterise the C. jejuni and C. coli LOS biosynthesis loci with special emphasis on their classes’ distribution and also to determine the role of LOS in mediating the host immune response. Analysis of the LOS locus gene content in 50 C. jejuni clinical isolates and 703 publicly available C. jejuni genome sequences revealed that the class B (Group 1) was the most abundant LOS locus class in C. jejuni. Two novel C. jejuni LOS types were identified from the GenBank database which may have arisen due to interspecies and intraspecies LOS gene recombination. In silico analysis of LOS locus gene content in 564 publicly available C. coli genome sequences identified previously unknown LOS inner core biosynthesis genes; all were located between waaF and gmhA and occurred in 5 C. coli LOS locus types (I, II, III, V, VIII). It was also determined that class III is the most abundant LOS locus type in C. coli and the environmental niches are the major reservoirs of C. coli. Moreover, this work highlighted that live and heat killed cells of both C. jejuni and C. coli, as well as, extracted LOS activate the NLRP3 [Nucleotide binding oligomerisation domain (NOD) like receptors with pyrin domain–containing 3] inflammasome dependent signalling in a human monocytic cell line, THP-1. However, C. jejuni 11168 LOS mutant live cells and its modified LOS with altered lipid A and lack of LOS core oligosaccharides both stimulated significantly reduced Caspase-1 and IL-1β compared to the wild-type 11168 live cells and LOS, which indicated that variation in LOS structure can alter NLRP3 inflammasome activation. This work extends the understanding of the Campylobacter LOS locus classification system and determines that LOS plays an important role in the development of host immune response during Campylobacter infection.