Fluorescent antibody technique to identify Azospirillum brasilense associated with roots of grasses

Bacteria associated with roots of grasses from Florida, Ecuador and Venezuela were isolated and their N₂-fixing ability was demonstrated by C₂H₂ reduction assay. The bacterial isolates have been classified as Azospirillum brasilense (formerly Spirillum lipoferum). These N₂-fixing isolates have been compared with several Brazilian strains. Fluorescent antibody (FA) techniques were used to assist identifying isolates of N₂-fixing bacteria from grass roots. Tests with antisera prepared against four strains of Azospirillum were used to define serological groups. Antigen-antibody specificity was demonstrated using both Azotobacter and Azospirillum antisera against known species of other soil microorganisms and numerous unidentified soil bacteria. Several applications of the FA technique are suggested to identify N₂-fixing bacteria associated with grass roots.