Methanosarcina semesiae sp nov., a dimethylsulfide-utilizing methanogen from mangrove sediment

Methanosarcina semesiae MD1(T) (T = type strain), a novel obligately methyl otrophic methanogenic archaeon is described. Strain MD1(T) was isolated fro m an enrichment on dimethylsulfide inoculated with mangrove sediment. The c ells were irregularly coccoid, non-motile, 1.4+/-0.2 mu m in diameter and s tained Gram-positive. The catabolic substrates used included dimethylsulfid e, methanethiol. methanol and methylated amines, but not acetate, formate, H-2/CO2 or a combination of these substrates. When cells grown on dimethyls ulfide were transferred to trimethylamine or methanol and vice versa, a lag phase was observed. The same lag phase occurred when cells grown on trimet hylamine were transferred to methanol and vice versa, indicating that for e ach substrate different enzymes were induced. Fastest growth occurred withi n 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 Naand 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 tri methylamine, respectively. Analysis of the 16S rRNA gene sequence showed th at strain MD1(T) was phylogenetically closely related to members of the gen us Methanosarcina, but clearly differed from all described species of this genus (94-97% sequence similarity).