Bacteria's ability to exchange genes amongst each other may occur more frequently and involve the transfer of even more genetic material than previously believed, a new study suggests. Such a robust and frequent version of horizontal gene transfer (HGT) would explain bacteria's ability to consistently generate genetic variability, rapidly adapt to diverse environments, and widely disperse genes encoding key survival factors, like antibiotic resistance, the authors say. Bacteriophages, viral parasites found in most bacteria, are key vehicles for HGT. Phages exploit the bacterial host's DNA replication machinery to transcribe, cleave, and package their DNA into capsids (viruses' protein shells), resulting in phage particles that can infect other cells. During this process, some bacterial DNA may also be packaged and transferred, but this mechanism, called transduction, is thought to be rare and accidental. Now, John Chen and colleagues have revealed a mode of transduction that occurs at frequencies 1,000 times higher than previously observed. They studied Staphylococcus aureus infected with prophage - a phage genome that has been integrated into the bacteria's genome - finding that the prophage did not excise from the bacterium's chromosome until late in the virus life cycle. As a result, the phage DNA replicated while still incorporated within the bacterial genome, and both viral and bacterial DNA were cut and packaged into capsids. Because phage stuff their capsids with DNA until they are physically full, adjacent bacterial DNA was also incorporated in the capsid. Bacteria often have genes for virulence and antibiotic resistance located close to virus excision sites, thus transduction can contribute to rapid transmission of drug resistance, the authors say. They suspect the mechanism they identified is universal among bacteria and are currently expanding their study to other species. In a related Perspective, Alan Davidson discusses the implications of these findings.
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Journal
Science