Mesorhizobium sediminum sp. nov., isolated from deep-sea sediment.

A novel Gram-staining-negative, short rod, non-motile, non-spore-forming, aerobic bacterium, designated strain YIM M12096T, was isolated from deep-sea sediment collected from the Indian Ocean. Optimal growth conditions of the strain were observed at 25-30 °C, pH 6.0 and in the presence of 3-5 % (w/v) NaCl. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain YIM M12096T was closely related to Nitratireductor indicus C115T (97.4 % 16S rRNA gene sequence similarity) and Mesorhizobium thiogangeticum SJTT (97.3 %). The strain, however, formed a robust clade with members of the genus Mesorhizobium in phylogenetic dendrograms generated with neighbour-joining, maximum-likelihood and maximum-parsimony trees. Analysis based on the sequence of housekeeping gene recA also gave a similar phylogenetic relationship, indicating that strain YIM M12096T is a member of the genus Mesorhizobium. DNA-DNA relatedness values between strain YIM M12096T and related type strains N. indicus CCTCC AB209298T and M. thiogangeticum DSM 17097T were 40.5 % and 36.7 %, respectively. Chemotaxonomic features of the isolate included phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine, an unidentified aminophospholipid and an unidentified phospholipid as its characteristic polar lipids and Q-10 as respiratory ubiquinone. Major fatty acids (>10 %) detected were C18 : 1ω7c and/or C18 : 1ω6c, 11-methyl-C18 : 1ω7c and cyclo-C19 : 0ω8c. Based on the chemotaxonomic properties and phylogenetic analyses, strain YIM M12096T is determined to be a member of the genus Mesorhizobium. The strain could be differentiated from the closely related species by the differences in physiological and biochemical properties supported by low DNA-DNA relatedness values. It is therefore concluded that strain YIM M12096T represents a novel species of the genus Mesorhizobium, for which the name Mesorhizobiumsediminum sp. nov. is proposed. The type strain is YIM M12096T (=CCTCC AB 2014219T=KCTC 42205T).