<i>Rhizobium acaciae</i> sp. nov., a new nitrogen-fixing symbiovar isolated from root nodules of <i>Acacia saligna</i> in Tunisia
Abstract
Three bacterial strains, 1AS11<sup>T</sup>, 1AS12 and 1AS13, members of the new symbiovar salignae and isolated from root nodules of <i>Acacia saligna</i> grown in Tunisia, were characterized using a polyphasic approach. All three strains were assigned to the <i>Rhizobium leguminosarum</i> complex on the basis of <i>rrs</i> gene analysis. Phylogenetic analysis based on 1734 nucleotides of four concatenated housekeeping genes (<i>recA</i>, <i>atpD</i>, <i>glnII</i> and <i>gyrB</i>) showed that the three strains were distinct from known rhizobia species of the <i>R. leguminosarum</i> complex and clustered as a separate clade within this complex. Phylogenomic analysis of 92 up-to-date bacterial core genes confirmed the unique clade. The digital DNA-DNA hybridization and blast-based average nucleotide identity values for the three strains and phylogenetically related <i>Rhizobium</i> species ranged from 35.9 to 60.0% and 87.16 to 94.58 %, which were lower than the 70 and 96% species delineation thresholds, respectively. The G+C contents of the strains were 60.82-60.92 mol% and the major fatty acids (>4 %) were summed feature 8 (57.81 %; C<sub>18 : 1</sub> ω7<i>c</i>) and C<sub>18 : 1</sub> ω7<i>c</i> 11-methyl (13.24%). Strains 1AS11<sup>T</sup>, 1AS12 and 1AS13 could also be differentiated from their closest described species (<i>Rhizobium indicum</i>, <i>Rhizobium laguerreae</i> and <i>Rhizobium changzhiense</i>) by phenotypic and physiological properties as well as fatty acid content. Based on the phylogenetic, genomic, physiological, genotypic and chemotaxonomic data presented in this study, strains 1AS11<sup>T</sup>, 1AS12 and 1AS13 represent a new species within the genus <i>Rhizobium</i> and we propose the name <i>Rhizobium acaciae</i> sp. nov. The type strain is 1AS11<sup>T</sup> (=DSM 113913<sup>T</sup>=ACCC 62388<sup>T</sup>).