The evolution of Campylobacter jejuni and Campylobacter coli

Abstract

The global significance of Campylobacter jejuni and Campylobacter coli as gastrointestinal human pathogens has motivated numerous studies to characterize their population biology and evolution. These bacteria are a common component of the intestinal microbiota of numerous bird and mammal species and cause disease in humans, typically via consumption of contaminated meat products, especially poultry meat. Sequence-based molecular typing methods, such as multilocus sequence typing (MLST) and whole genome sequencing (WGS), have been instructive for understanding the epidemiology and evolution of these bacteria and how phenotypic variation relates to the high degree of genetic structuring in C. coli and C. jejuni populations. Here, we describe aspects of the relatively short history of coevolution between humans and pathogenic Campylobacter, by reviewing research investigating how mutation and lateral or horizontal gene transfer (LGT or HGT, respectively) interact to create the observed population structure. These genetic changes occur in a complex fitness landscape with divergent ecologies, including multiple host species, which can lead to rapid adaptation, for example, through frame-shift mutations that alter gene expression or the acquisition of novel genetic elements by HGT. Recombination is a particularly strong evolutionary force in Campylobacter, leading to the emergence of new lineages and even large-scale genome-wide interspecies introgression between C. jejuni and C. coli. The increasing availability of large genome datasets is enhancing understanding of Campylobacter evolution through the application of methods, such as genome-wide association studies, but MLST-derived clonal complex designations remain a useful method for describing population structure.

Figure 1.

Allelic diversity in Campylobacter jejuni and Campylobacter coli genomes. (A) The average number of alleles per locus at 1035-core gene loci present 194 C. jejuni and C. coli isolates. (B) The distribution of allelic diversity showing that C. coli genes within the same isolate collection are, on average, more diverse, reflecting the deep branching 3-clade structure within this species.

Figure 2.

Population structure and evolution of Campylobacter jejuni and Campylobacter coli. The tube diagrams illustrate (A) the two main human disease-associated species, (B) clonal complex and clade structure in C. jejuni and C. coli, (C) an example of New Zealand lineage branching from the common ancestor of C. jejuni and C. coli, (D) the timescale of evolution based on Sheppard et al. (2010a), and (E) a despeciation evolutionary scenario, resulting from high recombination (R) among the species. C. upsaliensis, Campylobacter upsaliensis; C. helveticus, Campylobacter helveticus.