The finding has important biomedical implications because such gene-swapping, or lateral gene transfer, is the way many pathogenic bacteria pick up antibiotic resistance or become more virulent.

"To maintain effective treatments and develop new antibiotics, it's important to monitor the rates and patterns of lateral gene transfer," said team member Howard Ochman, a UA professor of biochemistry and molecular biophysics and a member of UA's BIO5 Institute.

The research also solves a long-standing evolutionary puzzle. Many scientists have argued that drawing traditional family trees does not make sense for bacteria, because their genomes represent a mix of genetic material from their parental cells and from other species of bacteria.

Ochman and his colleagues' work shows that bacterial lineages can still be traced by considering only the "traditional" forms of genetic inheritance. The widespread exchange of genes does not blur the line of descent because the acquired genes get lost from the genome at a later point or, if they do persist, the bacteria then transmit them to their offspring.

Being able to classify bacteria is crucial for medicine, Ochman said. "If you go to the doctor with strep throat he can be pretty certain that it's the result of an infection with a species of Streptococcus and can therefore prescribe an appropriate antibiotic. If you couldn't classify bacteria because they have genes from all over, doctors wouldn't be able to do this."

The research report is published in the current issue of PLoS Biology, available on www.plosbiology.org. Ochman's coauthors are Nancy Moran, UA Regents' Professor of ecology and evolutionary biology and BIO5 member, and Emmanuelle Lerat, now at Universite Claude Bernard (Lyon, France) and Vincent Daubin,
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Contact: Daniel Stolte
stolte@email.arizona.edu
520-626-4407
University of Arizona
7-Apr-2005