Horizontal Gene Transfer Widespread Among Bacteria

A group of investigators from the Massachusetts Institute of Technology (MIT) Department of Civil and Environmental Engineering and Department of Biological Engineering says that bacteria living today can easily pass on genes between each other.

The reason why this should be troubling to us is that the microorganisms can spread some of their more nefarious abilities, such as their resistance to particular drugs or the capability to infect human hosts with increased efficiency.

In order to transfer the genes, organisms use a mechanism called horizontal gene transfer (HGT). This enables them to move genes around freely and at great speeds, rivaling the rapidity of interpersonal data transfer methods we use today.

Details of the new investigation were published in the October 30 online issue of the top scientific journal Nature. The research group was led by MIT expert Eric Alm, who holds appointments with both departments involved in the new study.

During their latest experiments, the scientists were able to identify evidence that a gene-exchange process recently took place at a massive scale among numerous bacteria species. A total of 2,235 bacterial genomes, belonging to just as many species, were found to be involved in the exchange.

Researchers also found that these microorganisms exchanged about 10,000 unique genes through HGT alone, not counting the mutations they received from parents to offspring. These new discoveries can help account for the massive genetic variation bacteria display today.

“We are finding [completely] identical genes in bacteria that are as divergent from each other as a human is to a yeast. This shows that the transfer is recent; the gene hasn’t had time to mutate,” explains Alm, who holds an appointment as the MIT Karl Van Tassel Associate Professor.

“We were surprised to find that 60 percent of transfers among human-associated bacteria include a gene for antibiotic resistance,” lead paper author Chris Smillie explains. He is a graduate student of computational systems biology at MIT.

“Somehow, even though a billion years of genome evolution separate a bacterium living on a cow and a bacterium living on a human, both are accessing the same gene library. It’s powerful circumstantial evidence that genes are being transferred between food animals and humans,” Alm concludes.