Characterization of tropical tree rhizobia and description of Mesorhizobium plurifarium sp. nov.

A collection of strains isolated from root nodules of #Acacia$ species in Senegal was analysed previously by electrophoresis of total cell protein, auxanographic tests, rRNA-DNA hybridization, 16S rRNA gene sequencing, DNA base composition and DNA-DNA hybridization. Strains from #Acacia$ were shown to belong to two groups, #Sinorhizobium terangae$ and a so-called gel electrophoretic cluster U, which also included some reference strains from Brazil. Further taxonomic characterization of this group using the same techniques plus repetitive extragenic palindromic-PCR and nodulation tests is presented in this paper. Reference strains from Sudan and a number of new rhizobia isolated from nodules of #Acacia senegal$, #Acacia tortilis$ subsp. #raddiana$ and #Prosopis juliflora$ in Senegal were included. As a result of this polyphasic approach, the creation of a new species, #Mesorhizobium plurifarium$, is proposed for a genotypically and phenotypically distinct group corresponding to the former cluster U and containing strains isolated from #Acacia$, #Leucaena$, #Prosopis$ and #Chamaecrista$ in West Africa (Senegal), East Africa (Sudan) and South America (Brazil). The type strain of #Mesorhizobium plurifarium$ ORS 1032 has been deposited in the LMG collection as LMG 11892. (Résumé d'auteur