Isolation and characterization of 22 mesophilic methanococci

Twenty-two strains of mesophilic methanococci were isolated from salt marsh and other intertidal sediments of the southeastern United States. All the isolates were irregular cocci between 1 and 3 um in diameter, lysed rapidly in distilled water or 0.01% sodium dodecyl sulfate, used H 2 + CO 2 and formate as energy sources, and grew rapidly in salt-containing medium. The mol % G+C of six of the isolates was between 29.2 and 31.5. These isolates resembled Methanococcus voltae and required acetate, isoleucine, and leucine for growth. The mol % G+C of the remaining 16 isolates was between 32.6 and 34.4. They all grew autotrophically in mineral medium. The growth rates of eight of the autotrophic isolates were stimulated by either acetate or casamino acids. Although these isolates resembled several species of the genus Methanococcus, it was not possible to assign them to a species.