Rapid evolution and the importance of recombination to the gastro-enteric pathogen Campylobacter jejuni

Wilson, D. J., E. Gabriel, A. J. H. Leatherbarrow, J. Cheesbrough, S. Gee, E. Bolton, A. Fox, C. A. Hart, P. J. Diggle and P. Fearnhead (2009)
Molecular Biology and Evolution 26: 385-397. (pdf)

Responsible for the majority of bacterial gastro-enteritis in the developed world, Campylobacter jejuni is a pervasive pathogen of humans and animals, but its evolution is obscure. In this paper we exploit contemporary genetic diversity and empirical evidence to piece together the evolutionary history of C. jejuni and quantify its evolutionary potential. Our combined population genetics-phylogenetics approach reveals a surprising picture. C. jejuni is a rapidly evolving species, subject to intense purifying selection that purges 60% of novel variation, but possessing a massive evolutionary potential. The low mutation rate is offset by a large effective population size, so that a mutation at any site can occur somewhere in the population within the space of a week. Recombination has a fundamental role, generating diversity at twice the rate of de novo mutation, and facilitating gene flow between C. jejuni and its sister species C. coli. We attempt to calibrate the rate of molecular evolution in C. jejuni based solely on within-species variation. The rates we obtain are up to 1,000 times faster than conventional estimates, placing the C. jejuni – C. coli split at the time of the Neolithic revolution. We weigh the plausibility of such recent bacterial evolution against alternative explanations and discuss the evidence required to settle the issue.