Enhanced biofilm formation and multi-host transmission evolve from divergent genetic backgrounds inCampylobacter jejuni

Multicellular biofilms are an ancient bacterial adaptation that can offer a protective environment for survival in hostile habitats. In microaerophilic organisms like Campylobacter, biofilms can play a key role in transmission to humans as the bacteria are exposed to atmospheric oxygen concentrations when leaving the reservoir host gut. The genetic determinants of biofilm formation can differ between species but little is known about how strains of the same species achieve the biofilm phenotype with different genetic backgrounds. We take an integrated genomics approach to combine genome-wide association studies with traditional microbiology techniques to investigate the genetic basis of biofilm formation in 102 Campylobacter jejuni isolates. The study quantified biofilm formation among the isolates and identified hotspots of genetic variation in homologous sequence that corresponded to variation in biofilm phenotypes. In total, 46 genes showed a statistically robust association including those involved in adhesion, motility, nitrosative and oxidative stress. Previously reported and novel genes, containing associated elements, clustered on the genome - including 9 multi-gene transcriptional units. This is consistent with genetic linkage and the horizontal acquisition of biofilm genes in recombining organisms such as C. jejuni. The genes associated with biofilm formation were different in the host generalist ST-21 and ST-45 clonal complexes, which are frequently isolated from multiple host species and clinical samples, but both had enhanced biofilm formation compared to host specialists. This suggests the evolution of enhanced biofilm from different genetic backgrounds and a possible role in colonisation of multiple hosts and transmission to humans