MBE Advance Access published online on November 13, 2008
Molecular Biology and Evolution, doi:10.1093/molbev/msn264
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Research Article |
Rapid evolution and the importance of recombination to the gastro-enteric pathogen Campylobacter jejuni
1 Department of Maths and Statistics, Lancaster University, Lancaster LA1 4YF, UK
2 Department of Medicine, Lancaster University, Lancaster LA1 4YB, UK
3 Faculty of Veterinary Science, University of Liverpool, Leahurst, Neston CH64 7TE, UK
4 Preston Microbiology Services, Royal Preston Hospital, Lancashire Teaching Hospitals NHS Foundation Trust, Preston PR2 9HT, UK
5 Manchester Medical Microbiology Partnership, PO Box 209, Clinical Sciences Building, Manchester Royal Infirmary, Manchester M13 9WZ, UK
6 Division of Medical Microbiology, School of Infection and Host Defence, University of Liverpool, Liverpool L69 3GA, UK
* To whom correspondence should be addressed. E-mail djw{at}uchicago.edu. Present address: Department of Human Genetics, University of Chicago, 920 East 58th Street, CLSC 410, Chicago, IL 60637. Telephone 773-834-3936. Fax 773-834-0505.
Received for publication September 19, 2008. Accepted for publication November 6, 2008.
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.
Key Words: Campylobacter jejuni • molecular clock • recombination • selection • coalescent • Neolithic
Present address: Université d'Avignon, IUT STID, Site Agroparc, BP 1207, 84 911 Avignon, France. 
Deceased.
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