Food poisoning bacteria show signs of merging
25 April 2008
Research has shown that two species of bacteria known to cause serious food poisoning in people could be merging into one species. The team behind the study thinks that human activity - possibly intensive farming - may have created a new environment that allows increased gene exchange between the two bugs.
The findings, published in the journal Science, also suggest that the process by which new species evolve is common between animals and bacteria.
Campylobacter jejuni and C. coli are the most common bacterial causes of gastroenteritis in humans around the world. These bacteria live in the intestines of many animals and birds, including those reared for farming. The infection spreads by fecal matter from infected humans or animals getting into someone’s mouth, for example, by eating undercooked meat from an infected pig, cow or chicken.
The two types of bacterium are closely related, sharing around 87 per cent of their most conserved genes, but they are still distinct species. However, these species often swap genes, producing hybrid bacteria that are intermediate between the two types.
Now, researchers at the University of Oxford, led by Wellcome Trust Senior Research Fellow Professor Martin Maiden, have found evidence of extensive gene exchange between the two species that suggests C. coli and C. jejuni are, in fact, merging.
The researchers studied the genetic sequence of different bacterial isolates at the same seven conserved genes. They found that C. jejuni genes seen in C. coli hybrids looked the same as the C. jejuni genes found in farm animals and birds, but different to those found in wild birds. This led the researchers to suggest that farms and the modern agriculture techniques used on them could have provided an environment that encourages gene swapping between the two species.
The process by which these bacteria are merging is thought to be the opposite of speciation - where one or more new species evolves from a single existing species because of geographical isolation. C. coli hybrids containing C. jejuni genes were much more common than C. jejuni with C. coli genes, which suggests C. coli could be ‘despeciating’ - basically, turning into C. jejuni.
It is not yet known what these changes could mean in terms of human disease, but this work does show how human activity has the potential to influence the evolution of bacteria. Research is needed to investigate this ‘despeciation’ further and to see if this process is occurring in other types of bacteria.
References
Sheppard SK et al. Convergence of Campylobacter species: implications for bacterial evolution. Science 2008;320(5873):237-9.