Mesorhizobium acaciae sp. nov., isolated from root nodules of Acacia melanoxylon R. Br.

Three novel strains, RITF741T, RITF1220 and RITF909, isolated from root nodules of Acacia melanoxylon in Guangdong Province of China, have been previously identified as members of the genus Mesorhizobium, displaying the same 16S rRNA gene RFLP pattern. Phylogenetic analysis of 16S rRNA gene sequences indicated that the three strains belong to the genus Mesorhizobium and had highest similarity (100.0 %) to Mesorhizobium plurifarium LMG 11892T. Phylogenetic analyses of housekeeping genes recA, atpD and glnII revealed that these strains represented a distinct evolutionary lineage within the genus Mesorhizobium. Strain RITF741T showed >73 % DNA–DNA relatedness with strains RITF1220 and RITF909, but < 60 % DNA–DNA relatedness with the closest type strains of recognized species of the genus Mesorhizobium. They differed from each other and from their closest phylogenetic neighbours by presence/absence of several fatty acids, or by large differences in the relative amounts of particular fatty acids. While showing distinctive features, they were generally able to utilize a wide range of substrates as sole carbon sources based on API 50CH and API 20NE tests. The three strains were able to form nodules with the original host Acacia melanoxylon and other woody legumes such as Acacia aneura, Albizia falcataria and Leucaena leucocephala. In conclusion, these strains represent a novel species belonging to the genus Mesorhizobium based on the data obtained in the present and previous studies, for which the name Mesorhizobium acaciae sp. nov. is proposed. The type strain is RITF741T ( = CCBAU 101090T = JCM 30534T), the DNA G+C content of which is 64.1 mol% (T m).