It adds that the University of California, Berkeley's Jill Banfield spotted the enigmatic DNA elements when analyzing mud samples for signs of viruses that infect archaea. Instead, she and her colleagues uncovered long, linear pieces of DNA that appeared to harbor a particular pattern. They further found additional examples of these extrachromosomal elements within sediment samples from Colorado and other spots in California. As they report in a preprint posted to BioRxiv, Banfield and her colleagues found that these Borg elements have accumulated genes from Methanoperedens, the methane-oxidizing archaeon they appear to be associated with, and may augment its methane oxidation.
But what exactly the Borg are — the name was proposed by Banfield's son, according to Science — is unclear. "It is fascinating to ponder their possible evolutionary origins. Are they giant linear viruses or plasmids unlike anything previously reported? Alternatively, are they auxiliary chromosomes? Perhaps they were once a sibling Methanoperedens lineage that underwent gene loss and established a symbiotic association within Methanoperedens?" Banfield and her colleagues write in their preprint.