ISOLATION AND CHARACTERIZATION OF A DIMETHYL SULFIDE-DEGRADING METHANOGEN, METHANOLOBUS-SICILIAE HI350, FROM AN OIL-WELL, CHARACTERIZATION OF M-SICILIAE T4/MT, AND EMENDATION OF M-SICILIAE

We isolated strain HI350 from a gas and oil well in the Gulf of Mexico, characterized it, and found that it is closely related to Methanolobus siciliae T4/M(T) (T = type strain), which we also characterized. The previously published characterization of the type strain of M. siciliae was limited to the optimum temperature for growth, and our characterization suggested the species description given below. Cells are irregular, nonmotile, coccoid, and 1.5 to 3-mu-m in diameter. The catabolic substrates used include methanol, trimethylamine, and dimethyl sulfide, but not H-2-CO2, formate, or acetate. Growth is fastest in the presence of 0.4 to 0.6 M Na+, in the presence of 60 to 200 mM Mg2+, at pH 6.5 to 6.8, and at 40-degrees-C. Growth on trimethylamine is stimulated by yeast extract. An electrophoretic analysis confirmed that strain HI350 is closely related to strain T4/M(T) and indicated that major changes in the intracellular proteins of M. siciliae HI350 occur when the growth substrate is switched between dimethyl sulfide and trimethylamine.