Methylarcula marina gen. nov., sp nov and Methylarcula terricola sp nov.: novel aerobic, moderately halophilic, facultatively methylotrophic bacteriafrom coastal saline environments

A new genus, Methylarcula, with two new species, Methylarcula marina and Me thylarcula terricola, are proposed for strains h1(T) and h37(T) of moderate ly halophilic facultatively methylotrophic bacteria isolated from the coast al saline habitats. These methylobacteria are aerobic, Gram-negative, aspor ogenous, non-motile, colourless rods that multiply by binary fission. Their cellular fatty acids profiles consist primarily of straight-chain unsatura ted (C-18:1; 70-80%), saturated (C-18:0; 14-16%) and cyclopropane (C-19:0; 5-6%) acids. The major ubiquinone is Q-10. The dominant phospholipids are p hosphatidylethanolamine and phosphatidylcholine. Both strains could use met hylamine, some sugars and organic acids as carbon and energy sources. They grew well under optimal conditions (29-35 degrees C, pH 7.5-8.5. 0.5-1.0 M NaCl) and accumulated intracellularly poly-beta-hydroxybutyrate and the com patible solute ectoine. The ectoine pool was found to increase upon increas ing the external NaCl concentration and accounted for 18% of the dry cellul ar weight. Both strains oxidized methylamine by the N-methylglutamate (N-MG ) pathway enzymes (gamma-glutamylmethylamide synthetase/lyase and N-MG synt hetase/lyase) to formaldehyde and assimilated it via the icl(-) serine path way. The DNA G+C content was 60.4 mol% for Methylarcula marina h1(T) and 57 .1 mol% for Methylarcula terricola h37(T). The DNA-DNA hybridization value between strains h1 and h37 was 25-30%, although they had a low level of DNA relatedness (5-7%) with the type strains of the serine pathway methylobact eria belonging to the genera Methylobacterium, Aminobacter, Methylorhabdus and Methylopila. A comparative 16S rDNA sequence-based phylogenetic analysi s placed the two species of Methylarcula into a separate branch of the alph a-3 subclass of the Proteobacteria. The type strains of the new species are Methylarcula marina h1(T) (= VKM B-2159(T)) and Methylarcula terricola h37 (T) (= VKM B-2160(T)).