Genome-based reclassification of Azospirillum brasilense Az39 as the type strain of Azospirillum argentinense sp. nov.

Strain Az39 of is a diazotrophic plant growth-promoting bacterium isolated in 1982 from the roots of wheat plants growing in Marcos Juárez, Córdoba, Argentina. It produces indole-3-acetic acid in the presence of l-tryptophan as a precursor, grows at 20-38 °C (optimal 38 °C), and the cells are curved or spiral-shaped, with diameters ranging from 0.5-0.9 to 1.8-2.2 µm. They contain C, C and C 7/6 as the main fatty acids. Phylogenetic analysis of its 16S rRNA gene sequence confirmed that this strain belongs to the genus , showing a close relationship with Sp245, Sp7 and CC-Nfb-7. Housekeeping gene analysis revealed that Az39, together with five strains of the genus (Az19, REC3, BR 11975, MTCC4035 and MTCC4036), form a cluster apart from Sp245, Sp7 and CC-Nfb-7. Average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) between Az39 and the aforementioned type strains revealed values below 96 %, the circumscription limit for the species delineation (ANI: 95.3, 94.1 and 94.0 %; dDDH: 62.9, 56.3 and 55.6 %). Furthermore, a phylogeny evaluation of the core proteome, including 809 common shared proteins, showed an independent grouping of Az39, Az19, REC3, BR 11975, MTCC4035 and MTCC4036. The G+C content in the genomic DNA of these six strains varied from 68.3 to 68.5 %. Based on the combined phylogenetic, genomic and phenotypic characterization presented here, we consider that strain Az39, along with strains Az19, REC3, BR 11975, MTCC4035 and MTCC4036, are members of a new species, for which the name sp. nov. is proposed. The type strain is Az39 (=LBPCV39=BR 148428=CCCT 22.01).