Aspects of nitrogen fixation and denitrification by Azospirillum

Model experiments were performed to investigate the nitrogen fixation (C₂H₂ reduction) and denitrification (N₂O formation) capabilities of Azospirillum spp. in association with wheat. Plants and bacteria were grown together for a week and then assayed for activities. This association performed C₂H₂ reduction or N₂O formation, depending on the concentrations of nitrate and oxygen in the vessels. Both activities depended on the Azospirillum strains used. The newly isolated Azospirillum amazonense strains Y1 and Y6 showed significant C₂H₂ reduction and low N₂O formation in association with wheat under the conditions employed and are possibly useful in practice. A cell-free preparation from Azospirillum brasilense Sp 7 possessed a cytochrome cd type dissimilatory nitrite reductase.