Abstract
In this study, we investigated various chromosomal and symbiotic markers in 40 bacterial strains that nodulating an invasive alien Acacia salicina Lindl. In Tunisia never described worldwide. Our findings showed that the native rhizobia in Tunisia associated to A. salicina are grouped into eight distinct RAPD electrophoretic types (RETs) (genotypes). Sequence analyses of rrs and three housekeeping genes (recA, rpoB and glnII) assigned sixteen isolates to three putative new lineages within Bradyrhizobium genus. Seven strains were clustered with B. rifense CTAW71T with low bootstrap support (91%), five strains were grouped with B. niftali CNPSo3448T with a very low bootstrap support (60%), and four strains occupied a separate position between B. shewense ERR11T and B. centrosematis A9T. All strains were not able to grow at 37°C, pH 12 and more than 0.5% NaCl and showed a different response to different antibiotics, with no growth in presence of Gentamicin. Based on nodC phylogeny and cross inoculation tests, these 16 strains are clustered within the two symbiovar retamae (six strains) and cyanophyllae (ten strains). According to the symbiotic gene sequence and the nodulation phenotype with A. salicina and A. saligna, the reference strain B. diversitatis CNPSo4019T would be, interestingly, considered for the first time as a new member of the symbiovar cyanophyllae.