Comparative genomics and genome biology of <i>Campylobacter showae</i>

<i>Campylobacter showae</i> a bacterium historically linked to gingivitis and periodontitis, has recently been associated with inflammatory bowel disease and colorectal cancer. Our aim was to generate genome sequences for new clinical <i>C. showae</i> strains and identify functional properties explaining their pathogenic potential. Eight <i>C. showae</i> genomes were assessed, four strains isolated from inflamed gut tissues from paediatric Crohn’s disease patients, three strains from colonic adenomas, and one from a gastroenteritis patient stool. Genome assemblies were analyzed alongside the only 3 deposited <i>C. showae</i> genomes. The pangenome from these 11 strains consisted of 4686 unique protein families, and the core genome size was estimated at 1050 ± 15 genes with each new genome contributing an additional 206 ± 16 genes. Functional assays indicated that colonic strains segregated into 2 groups: adherent/invasive vs. non-adherent/non-invasive strains. The former possessed Type IV secretion machinery and S-layer proteins, while the latter contained Cas genes and other CRISPR associated proteins. Comparison of gene profiles with strains in Human Microbiome Project metagenomes showed that gut-derived isolates share genes specific to tongue dorsum and supragingival plaque counterparts. Our findings indicate that <i>C. showae</i> strains are phenotypically and genetically diverse and suggest that secretion systems may play an important role in virulence potential.