Molecular and physiological comparison of Azospirillum spp. isolated from Rhizoctonia solani mycelia, wheat rhizosphere, and human skin wounds

Four phenotypically similar bacterial strains isolated from fungal, plant, and human sources were identified as Azospirillum species. Strains RC1 and LOD4 were isolated from the mycelium of the apple root pathogen Rhizoctonia solani AG 5 and from the rhizosphere of wheat grown in apple orchard soil, respectively. Strains C610 and F4626 isolated from human wounds were previously misclassified as Roseomonas genomospecies 3 and 6. All four strains demonstrated close similarities in 16S rRNA gene sequences, having ≥97% identity to Azospirillum brasilense type strain ATCC 29145 and <90% identity to Roseomonas gilardii, the Roseomonas type strain. Extensive phenotypic similarities among the four strains included the ability of free-living cells to fix N₂. Cells of strains RC1, LOD4, and C610 but not of strain F4626 could be induced to flocculate by incubation with 10 mmol·L^-1 glycerol or fructose in medium containing 0.5 mmol·L^-1 NO₃^-. Our results indicate a wide range of potential sources for Azospirillum spp. with the isolation of Azospirillum spp. from human wounds warranting further investigation.