Nitrogenase activity in mixed cultures of Azospirillum with other bacteria

Abstract

Summary Department of General Microbiology, Institute of Microbiology, Federal University of Rio de Janeiro, Brazil Fifty Gram-negative and 29 Gram-positive bacteria were tested in co-cultures in nitrogen-free, semisolid medium with either Azospirillum brasilense Sp7 or Azospirillum lipoferum Br17. Among the 79 bacteria examined, 12 Gram-negative and 7 Gram-positive did not exert any effect on the nitrgenase activity either in A. brasilense or A. lipoferum. The other bacteria stimulated or inhibited the nitrogenase either in one or both Azospirillum species. In several cases the same accompanying bacterium affected in a different way the two species of Azospirillum tested, stimulating one and inhibiting the other or acting on one, but not affecting the other. The active factors, produced by the accompanying bacteria, seem to be of oligodynamic nature. The capacity of producing these factors seems to be an individual pattern of particular strains, and no correlation was found between the taxonomical position of the accompanying bacterium and its manner of affecting Azospirillum.