Genome-based reclassification of Azospirillum brasilense Sp245 as the type strain of Azospirillum baldaniorum sp. nov

Azospirillum sp. strain Sp245(T), originally identified as belonging to Azospirillum brasilense, is recognized as a plant-growth-promoting rhizobacterium due to its ability to fix atmospheric nitrogen and to produce plant-beneficial compounds. Azospirillum sp. Sp245(T) and other related strains were isolated from the root surfaces of different plants in Brazil. Cells are Gram-negative, curved or slightly curved rods, and motile with polar and lateral flagella. Their growth temperature varies between 20 to 38 degrees C and their carbon source utilization is similar to other Azospirillum species. A preliminary 16S rRNA sequence analysis showed that the new species is closely related to A. brasilense Sp7(T) and A. formosense CC-Nfb-7(T). Housekeeping genes revealed that Azospirillum sp. Sp245T, BR 12001 and Vi22 form a separate cluster from strain A. formosense CC-Nfb-7(T), and a group of strains closely related to A. brasilense Sp7(T). Overall genome relatedness index (OGRI) analyses estimated based on average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) between Azospirillum sp. Sp245(T) and its close relatives to other Azospirillum species type strains, such as A. brasilense Sp7(T) and A. formosense CC-Nfb-7(T) , revealed values lower than the limit of species circumscription. Moreover, core-proteome phylogeny including 1079 common shared proteins showed the independent clusterization of A. brasilense Sp7(T), A. formosense CC-Nfb-7(T) and Azospirillum sp. Sp245(T), a finding that was corroborated by the genome clustering of OGRI values and housekeeping phylogenies. The DNA G+C content of the cluster of Sp245(T) was 68.4-68.6 %. Based on the phylogenetic, genomic, phenotypical and physiological analysis, we propose that strain Sp245(T) together with the strains Vi22 and BR12001 represent a novel species of the genus Azospirillum, for which the name Azospirillum baldaniorum sp. nov. is proposed. The type strain is Sp245(T) (=BR 11005(T)=IBPPM 219(T)) (GCF_007827915.1, GCF_000237365.1, and GCF_003119195.2).