Methanococcoides vulcani sp. nov., a marine methylotrophic methanogen that uses betaine, choline and N,N-dimethylethanolamine for methanogenesis, isolated from a mud volcano, and emended description of the genus Methanococcoides

A novel, strictly anaerobic, methylotrophic marine methanogen, strain SLH33^T, was isolated from deep sediment samples covered by an orange microbial mat collected from the Napoli Mud Volcano. Cells of strain SLH33^T were Gram-stain-negative, motile, irregular cocci that occurred singly. Cells utilized trimethylamine, dimethylamine, monomethylamine, methanol, betaine, N,N-dimethylethanolamine and choline (N,N,N-trimethylethanolamine) as substrates for growth and methanogenesis. The optimal growth temperature was 30 °C; maximum growth rate was obtained at pH 7.0 in the presence of 0.5 M Na⁺. The DNA G+C content of strain SLH33^T was 43.4 mol%. Phylogenetic analyses based on 16S rRNA gene sequences placed strain SLH33^T within the genus Methanococcoides. The novel isolate was related most closely to Methanococcoides methylutens TMA-10^T (98.8 % 16S rRNA gene sequence similarity) but distantly related to Methanococcoides burtonii DSM 6242^T (97.6 %) and Methanococcoides alaskense AK-5^T (97.6 %). DNA–DNA hybridization studies indicated that strain SLH33^T represents a novel species, given that it shared less than 16 % DNA–DNA relatedness with Methanococcoides methylutens TMA-10^T. The name Methanococcoides vulcani sp. nov. is proposed for this novel species, with strain SLH33^T ( = DSM 26966^T = JCM 19278^T) as the type strain. An emended description of the genus Methanococcoides is also proposed.