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Title: Progressive genome-wide introgression in agricultural Campylobacter coli

item SHEPPARD, SAMUEL - University Of Oxford
item DIDELOT, XAVIER - University Of Oxford
item JOLLEY, KEITH - University Of Oxford
item DARLING, AARON - University Of California
item KELLY, DAVID - University Of Sheffield
item COLLES, FRANCES - University Of Oxford
item STRACHEN, NORVAL - University Of Aberdeen
item OGDEN, IAN - University Of Aberdeen
item FORBES, KEN - University Of Aberdeen
item FRENCH, NIGEL - Massey University
item CARTER, PHILIP - Institute Of Environmental Science And Research
item Miller, William - Bill

Submitted to: Proceedings of the National Academy of Sciences (PNAS)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/21/2012
Publication Date: 12/20/2012
Citation: Sheppard, S.K., Didelot, X., Jolley, K.A., Darling, A.E., Kelly, D., Colles, F.M., Strachen, N.J., Ogden, I.D., Forbes, K.J., French, N., Carter, P., Miller, W.G. 2012. Progressive genome-wide introgression in agricultural Campylobacter coli. Proceedings of the National Academy of Sciences. 22:1051-1064.

Interpretive Summary: Campylobacters are one of the leading causes of bacterial food-borne illness worldwide. The Campylobacter species most associated with human food-borne illnesses are C. jejuni and C. coli. These two species are isolated often from birds and food animals. Campylobacter jejuni and C. coli are highly related in gene content and chromosomal genetic organization; however, core proteins of the two species are about 10% different on average. Nevertheless, even with this divergence in protein sequence, the two Campylobacter species exchange DNA, due in part to the natural transformation abilities of Campylobacter, where DNA can be taken up by cells and incorporated into the chromosome. Campylobacter coli strains fall into two major groups and each group has been accumulating C. jejuni DNA. In one group, almost a quarter of the C. coli genome has been replaced with DNA originating in C. jejuni; in the other group, the degree of C. jejuni DNA accumulation is much lower (around 10%). The interchange of DNA between the species would be expected to lead perhaps to niche colonization drift and the migration of C. coli into new habitats with possible increases in virulence and C. coli-caused human illness.

Technical Abstract: Hybridization between distantly related organisms can facilitate rapid adaptation but is constrained by epistatic fitness interactions. The zoonotic pathogens Campylobacter coli and C. jejuni differ from each other at an average of nearly 40 amino acids per gene. Nevertheless, they have started to exchange substantial amounts of DNA. We show that a single C. coli lineage successfully colonized the agricultural niche. Descendants fall into two groups, the ST-828 and ST-1150 clonal complexes both of which have been progressively accumulating C. jejuni DNA. The 1150 complex is less common but has undergone a substantially higher amount of introgression, leading to replacement of up to 23% of the C. coli core genome as well as import of novel DNA. By contrast, 828 complex strains have 10-11% introgressed DNA and C. jejuni and non-agricultural C. coli strains each have less than 2%. These findings highlight the importance of recombination in pathogen emergence and shows remarkable interchangeability of basic cellular machinery even after a prolonged period of independent evolution.