The root associated, nitrogen fixing bacterium Azospirillum brasilense produces catechol type siderophores. Cells of A. brasilense strain SPF94 have been mutagenized with transposon Tn5 and mutants have been isolated that were impaired in the ability to take up iron from the medium. A preliminary characterization of these mutants including: growth capability in iron-limiting medium, excretion of catechol compounds that are presumed to be the siderophores of the species, and uptake of super(55)Fe to the cells is reported