A polyphasic taxonomic approach was used to characterize a presumptively novel diazotrophic bacterium, designated strain CC-YTH430T, isolated from a compost sample in Taiwan. Cells of strain CC-YTH430T were found to be Gram-stain negative, facultative anaerobic rods that formed yellow-colored colonies on nutrient agar. Cell growth occurred at 15-40 °C, pH 5.0-9.0 and in the presence of 0-2% NaCl. Strain CC-YTH430T resembled Mesorhizobium species while sharing high pair-wise 16S rRNA gene sequence similarities with Mesorhizobium silamurunense, Mesorhizobium thiogangeticum, Mesorhizobium plurifarium, Mesorhizobium tamadayense, Mesorhizobium amorphae (96.9% each), Mesorhizobium sediminum (96.8%), and Mesorhizobium soli (96.5%) and < 96.5% similarity to other species. Strain CC-YTH430T showed 78.8-79.7% average nucleotide identity compared to the type strains of M. amorphae, M. plurifarium, M. soli, M. tamadayense and M. wenxiniae. The N2-fixing activity of strain CC-YTH430T was 0.2 nmol ethylene h-1 at 30 °C. The respiratory system was ubiquinone 10 (Q-10) and the DNA G+C content was 62.0 ± 0.2 mol%. The major fatty acids (> 5%) were C16:0, C17:0 cyclo, C19:0 cyclo ω8c, C14:0 3OH/C16:1 iso I and C18:1ω7c/C18:1ω6c. The polar lipid profile contained diphosphatidylglycerol, phosphatidylglycerol, phosphatidylcholine, phosphatidylmonomethylethanolamine and an unidentified aminolipid in major amounts. In addition, phosphatidylethanolamine, an unidentified lipid and several unidentified polar lipids were also found in moderate-to-trace amounts. Based on the phylogenetic, phenotypic and chemotaxonomic features, strain CC-YTH430T is proposed to represent a novel Mesorhizobium species, for which the name Mesorhizobium composti sp. nov. (type strain CC-YTH430T = BCRC 81024T = JCM 31762T) is proposed.
Keywords: Compost; Mesorhizobium composti; Phyllobacteriaceae; Polyphasic taxonomy.