Multilocus sequencing analysis of the rhizobial symbionts isolated from Acacia salicina (Lindl.) grown in different regions in Tunisia reveals putative novel Bradyrhizobium species

In this study, we investigated various chromosomal and symbiotic markers in 40 bacterial strains that nodulate an invasive alien plant, Acacia salicina Lindl. in Tunisia. Our findings showed that the native rhizobia associated to A. salicina are grouped into eight distinct RAPD electrophoretic types (RETs) (genotypes). Sequence analyses of rrs gene and three housekeeping genes (recA, rpoB and glnII) assigned sixteen isolates to three putative new lineages within the genus Bradyrhizobium. Seven strains clustered with B. rifense CTAW71^T with a 91% bootstrap support, five strains grouped with B. niftali CNPSo3448^T with a very low bootstrap support (60%), and four strains formed a group phylogenetically related with B. shewense ERR11^T and B. centrosematis A9^T. Based on nodC phylogeny and cross inoculation tests, the 16 strains are clustered within symbiovar retamae (six strains) and cyanophyllae (ten strains). Moreover, we showed by the first time in this work that the type strains B. diversitatis CNPSo4019^T and B. xenonodulans 14AB^T, which nodulated soybean and A. dealbata respectively, belong to the symbiovar cyanophyllae according to the results of the nodC gene analysis.