METHANOBACTERIUM SUBTERRANEUM SP. NOV., A NEW ALKALIPHILIC, EURYTHERMIC AND HALOTOLERANT METHANOGEN ISOLATED FROM DEEP GRANITIC GROUNDWATER

Deep subterranean granitic aquifers have not been explored regarding m ethanogens until now. Three autotrophic methane-producing Archaea were isolated from deep granitic groundwater at depths of 68, 409 and 420 m, These organisms were non-motile, small, thin rods, 0.1-0.15 mu m in diameter, and they could use hydrogen and carbon dioxide or formate a s substrates for growth and methanogenesis, One of the isolates, denot ed A8p, was studied in detail. It grew with a doubling time of 2.5 h u nder optimal conditions (20-40 degrees C, ph 7.8-8.8 and 0.2-1.2 M NaC l), Strain A8p is eurythermic as it grew between 3.6 and 45 degrees C, It was resistant to up to 20 mg bacitracin l(-1). The G+C content was 54.5 mol%, as determined by thermal denaturation, Phytogenetic studie s based upon 16S rRNA gene sequence comparisons placed the isolate A8p in the genus Methanobacterium, Phenotypic and phylogenetic characters indicate that the alkaliphilic, halotolerant strain A8p represents a new species. We propose the name Methanobacterium subterraneum for thi s species, and strain A8p (= DSM 11074(T)) is the type strain.