How microbes “retweet” antibiotic resistance

Haley Bridger, November 10th, 2011
  • Researchers looked in more than 2,000 bacterial genomes for gene transfers,
    including the genome of Salmonella typhimurium, shown in red in this color-
    enhanced scanning electron micrograph.
    Rocky Mountain Laboratories, NIAID, NIH

Just as researchers come together to share great ideas and new techniques, resourceful bacteria share their innovations, too. Eric Alm, an associate member of the Broad Institute and associate professor at MIT, was one of more than 30 speakers to share his work with the rest of the Broad community at the Broad Retreat, which took place on Monday and Tuesday. Eric reminded us that humans are largely outnumbered: for every human cell in our body, there are ten microbes living on and within us. And when it comes to exchanging information, they are quick.

Eric’s work on how bacteria swap genetic information appeared last week in Nature. Most of the time, when scientists talk about the transfer of genetic material from one organism to another, they are referring to the genetic material that a parent passes down to a child when the child is conceived. This is called vertical gene transfer. However, some organisms, such as bacteria, are able to give pieces of genetic material to one another in the way that humans might share a link on Facebook or Twitter – once one person finds something, she can rapidly share it with her friends, who can share it with their friends, and so on. The genetic innovations that bacteria share contribute to traits that help them survive, such as antibiotic resistance.

Eric and his team wanted to find out what factors influence the flow of genes among bacteria. They wondered if things like physical distance or the environments in which bacteria thrive might play a role in how rapidly genetic information is shared across species. They report many gene transfers among bacteria from different parts of the tree of life and across continents, with more than 43 instances of antibiotic-resistance genes crossing between countries.

Eric and his colleagues found that where a bacterium makes its home (which is often inside of us) has a big impact on gene exchange – it’s more important than geographic or evolutionary distance. They also found that, even in distantly related bacteria, many recently transferred genes are known to play an important role in disease. They suggest that other transferred genes whose functions are not yet known could potentially play a role in disease too – following up on these genes could reveal how antibiotic resistance spreads and help in the search for new drug targets.

Other researchers at the Broad, including Bruce Birren’s group, are also studying and cataloging the microorganisms living on your skin, in your mouth, in your gut, and elsewhere. If you’re curious to learn more, you can read about their ongoing efforts as part of the Human Microbiome Project, visit the Alm lab’s web site, or read more about the bacterial gene marketplace on Discover’s “Not Exactly Rocket Science” blog.