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Thursday, November 10, 2011

Microbial gene transfer


If we multicellular organisms want to transfer genes around, we have to reproduce.  Not so for bacteria, which are able to receive and donate genes to one another via horizontal gene transfer (HGT).  Just how common is this practice among the microbes? Eric Alm led a team of scientists from MIT in determining the frequency and specificity of these transfers.

HGT occurs when one bacterium transfers one or more genes to another completely unrelated bacterium, often by injecting the DNA straight through the recipient’s cell wall.  The two microorganisms don’t even have to be of the same species, proximity is the main limiting factor.  In fact, the researchers found over 10,000 cases of transfer between 2,235 different bacterial genomes.

Having the donor and recipient occupy the same ecological niche appears to be key for successful gene transfer.  For example, HGT was most common in bacteria with the same oxygen tolerance, or for those living in the same part of the body.

Why is HGT important?  Fully sixty percent of the transfer events involving human-associated bacteria included an antibiotic resistance gene.  Forty-two of these genes were found in the bacteria of both people and livestock, and on forty-three occasions antibiotic resistance genes had moved across national borders.  Clearly, we need to rethink our agricultural practices, especially the adding of prophylactic antibiotics to animal feed, a convention that is already banned in many European countries.