Comparative pangenomics of Campylobacter species

Bacterial genome sequencing has become very popular over the last 15 years in the field of bacterial genomics and evolution with over >1000 genome sequences generated for the zoonotic Campylobacter jejuni and Campylobacter coli species. The rapid improvement of culture and sequencing techniques has led to isolation and sequencing of new Campylobacter species from a variety of sources including birds, mammals, reptiles and the environment. Inter-species recombination has been demonstrated for C. jejuni and C. coli, but little is known about recombination between other species in the genus. We analysed the population genomic structure of whole genome sequenced isolates from different Campylobacter species using pangenome and phylogenetic analyses to investigate core and accessory gene variation and putative gene function. Characterizing the extend of genome segregation among multiple Campylobacter species isolated from the same and different hosts improved understanding of how ecology (physical isolation) maintains species and the extent to which intrinsic mechanistic and adaptive barriers are eroded when species cohabit. This broadly defines the limit of interspecies recombination and the non-reducible pangenomically-defined species. This raises important questions about the nature of species specific recombinational barriers, the genes that constitute the inter-species mobilome and the emergence of zoonoses through reticulate evolution in agricultural animals.