Meet the Borg
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You might not think there are many cutting edge scientific discoveries waiting to be uncovered in a pile of mud. But earlier this year, Professor Jill Banfield, a microbiologist from the University of California, Berkeley, proved that the best scientific discoveries can be found even in the most unlikely places.
Banfield and her team were studying how microbes influence the carbon cycle - the way in which the carbon atoms are recycled from the air into living things and then back again. In particular, she was curious about the role of extrachromosomal elements - bits of DNA that float around outside the main microbial genome. Extrachromosomal elements often carry non-essential but useful genes that microbes can share between them. For example, genes for antimicrobial resistance are carried on small circles of DNA known as plasmids, which get swapped between bacteria and help to spread antibiotic resistance through the population.
Banfield and her team set about squelching through the Californian mud looking for bugs containing genes that could be involved in the carbon cycle. One of the microbes they found was a bacteria-like microbe called Methanoperedens (strictly speaking, a member of the kingdom of archaea, and not a bacterium at all). When they took a closer look at these bugs, they noticed something very strange going on with their extrachromosomal DNA.
While most bacterial plasmids are circles of DNA typically anywhere between about 500 to 2,500 ‘letters’, or bases, long these Methanoperedens microbes contained huge, linear pieces of DNA with 600,000-1 million base pairs, making them up to a third of the length of the main archaeal genome. Further inspection of the gigantic structures revealed that they carried many new genes that have been scavenged, collected, or otherwise assimilated from other organisms in the same environment.
These extrachromosomal elements were unlike anything Banfield had ever seen before, so she needed to come up with a name for them. In a discussion with her son over thanksgiving dinner, he suggested the name ‘Borg’ - after the legendary Star Trek villains - because of their ability to assimilate. And just like that - the biological Borgs had landed.
Maintaining huge molecular structures like Borgs is energetically expensive - so they must offer some benefit to the archaea who carry them. The Borgs found by Banfield and her team were associated with Methanoperedens achaea, which digest the carbon-based gas methane, suggesting that Borgs may be specifically involved in that process. But further genetic analysis of Borgs suggests that they may carry many more useful genes that they’ve pinched from their neighbours, allowing them to act as gigantic, floating molecular toolboxes.
Banfield immediately saw the technological potential of Borgs, exclaiming to Twitter that she ‘hasn’t been this excited since CRISPR’. She hopes that one day we will be able to recruit the Borgs and use them for our own purposes, including controlling greenhouse gases like methane in the fight against climate change. So, maybe not such a baddie after all.
References:
Borgs are giant extrachromosomal elements with the potential to augment methane oxidation, Biorxiv
Massive DNA 'Borg' structures perplex scientists, Nature
Mysterious New 'Borg' DNA Seems to Assimilate Genes From Different Organisms, Science Alert
Mysterious DNA sequences, known as ‘Borgs,' recovered from California mud, Science
