Methanosarcina semesiae MD1T (T = type strain), a novel obligately methylotrophic methanogenic archaeon is described. Strain MD1T was isolated from an enrichment on dimethylsulfide inoculated with mangrove sediment. The cells were irregularly coccoid, non-motile, 1.4+/-0.2 microm in diameter and stained Gram-positive. The catabolic substrates used included dimethylsulfide, methanethiol, methanol and methylated amines, but not acetate, formate, H2/CO2 or a combination of these substrates. When cells grown on dimethylsulfide were transferred to trimethylamine or methanol and vice versa, a lag phase was observed. The same lag phase occurred when cells grown on trimethylamine were transferred to methanol and vice versa, indicating that for each substrate different enzymes were induced. Fastest growth occurred within a temperature range of 30-35 degrees C and a pH of 6.5-7.5. Both Na+ and Mg2+ were required for growth, with maximum growth rates at 200-600 mM Na+ and 20-100 mM Mg2+. The cells exhibited specific growth rates (h-1) of 0.07+/-0.02, 0.15+/-0.04 and 0.18-/+0.05 on dimethylsulfide, methanol and trimethylamine, respectively. Analysis of the 16S rRNA gene sequence showed that strain MD1T was phylogenetically closely related to members of the genus Methanosarcina, but clearly differed from all described species of this genus (94-97% sequence similarity).


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