Mesorhizobium shonense sp nov., Mesorhizobium hawassense sp nov and Mesorhizobium abyssinicae sp nov., isolated from root nodules of different agroforestry legume trees

A total of 18 strains, representing members of the genus Mesorhizobium, obtained from root nodules of woody legumes growing in Ethiopia, have been previously shown, by multilocus sequence analysis (MLSA) of five housekeeping genes, to form three novel genospecies. In the present study, the phylogenetic relationship between representative strains of these three genospecies and the type strains of their closest phylogenetic neighbours Mesorhizobium plurifarium, Mesorhizobium amorphae, Mesorhizobium septentrionale and Mesorhizobium huakuii was further evaluated using a polyphasic taxonomic approach. In line with our earlier MLSA of other housekeeping genes, the phylogenetic trees derived from the atpD and glnII genes grouped the test strains into three well-supported, distinct lineages that exclude all defined species of the genus Mesorhizobium. The DNA DNA relatedness between the representative strains of genospecies I-III and the type strains of their closest phylogenetic neighbours was low (<= 59%). They differed from each other and from their closest phylogenetic neighbours by the 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 and nitrogen sources. The strains belonging to genospecies I, II and III therefore represent novel species for which we propose the names Mesorhizobium shonense sp. nov., Mesorhizobium hawassense sp. nov. and Mesorhizobium abyssinicae sp. nov. The isolates AC39a(T) (=LMG 26966(T)=HAMBI 3295(T)), AC99b(T) (=LMG 26968(T)=HAMBI 3301(T)) and AC98c(T) (=LMG 26967(T)=HAMBI 3306(T)) are proposed as type strains for the respective novel species.