Borg (microbiology)
Borgs are large (up to ~1 Mbp) extrachromosomal linear DNA elements found in methanotrophic archaea (specifically Methanoperedens spp.) that live in oxygen-starved environments such as deep mud. They have been found in organisms isolated from wetland, aquifer, and riverbed environments, as well as a deserted mercury mine, in California and Colorado.