A newly-isolated marine methanogen harbors a small cryptic plasmid.

Of 21 recently isolated strains of methanococci, one was found to harbor a small, cryptic, low copy number plasmid. Reproducible recovery was achieved by alkaline lysis of cells pretreated with proteinase K in an osmotically stabilizing buffer. The plasmid was found to contain a single AvaI site. No homology was detected between the plasmid and DNA from any of the other new strains or from five known species of methanococci.