Definition of two new symbiovars, sv. lupini and sv. mediterranense, within the genera Bradyrhizobium and Phyllobacterium efficiently nodulating Lupinus micranthus in Tunisia

Abstract

In this study, a polyphasic approach was used to analyze three representative strains (LmiH4, LmiM2 and LmiT21) from a collection of six previously described strains isolated in Tunisia from root nodules of Lupinus micranthus. The phylogenetic analysis of the concatenated rrs, recA and glnII genes showed that strain LmiH4 had 100% concatenated gene sequence identity with the type strain Bradyrhizobium retamae Ro19T. Similarly, strain LmiM2 shared 100% concatenated gene sequence identity with the species Bradyrhizobium valentinum LmjM3T. However, strain LmiT21 showed an identical concatenated gene sequence with reference strain Phyllobacterium sophorae CCBAU03422T. The recA-glnII concatenated protein-coding genes used produced incongruent phylogenies compared with 16S rDNA phylogeny. The nodC gene analysis showed that the strains were phylogenetically divergent to the Bradyrhizobium symbiovars defined to date, and represented two new symbiovars. Plant infection analysis revealed that the three strains showed moderate host range and symbiotic specificities.Based on their symbiotic characteristics, we propose that the three strains isolated from Lupinus micranthus nodules belong to two new symbiovars, with the first denominated lupini within the two species Bradyrhizobium valentinum (type strain LmiM2) and B. retamae (type strain LmiH4), and the second denominated mediterranense within the species P. sophorae (type strain LmiT21).