Prevalence of Azospirillum spp. in the rhizosphere of tropical plants

Azospirillum cultures were isolated from the roots of a variety of tropical plants. Presumptive isolates from selective medium were identified by biochemical and serological methods. Forty-eight percent of the isolates were identified as A. lipoferum and the rest as A. brasilense, nir + or nir − . All of the isolates tested exhibited at least one heat-labile antigen with one or more of the three whole-cell reference antisera. Isolates identified as A. lipoferum were very similar to the reference strain SP59, while those identified as A. brasilense showed a greater degree of antigenic and biochemical diversity. No cross-reaction was detected between the four reference antisera used and strains of Azotobacter beijerinckia, A. chroococcum, A. vinelandii, Azomonas macrocytogenes, and A. agilis.