Browsing by Author "Christine A. Scott"

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    Nitrogenase Activity and Nitrate Respiration in Azospirillum spp.
    (1979) David B. Scott; Christine A. Scott; Johanna Dobereiner
    The interaction between nitrate respiration and nitrogen fixation in Azoxpirillum lipoferum and A. hraxilenxe was studied. All strains examined were capable of nitrogen fixation (acetylene reduction) under conditions of severe oxygen limitation in the presence of nitrate. A lag phase of about 1 h was observed for both nitrate reduction and nitrogenase activity corresponding to the period of induction of the dissimilatory nitrate reductase. Nitrogenase activity ceased when nitrate was exhausted suggesting that the reduction of nitrate to nitrite, rather than denitrifi-cation (the further reduction of nitrite to gas) is coupled to nitrogen fixation. The addition of nitrate to nitrate reductase negative mutants (nr-) of Azoxpirillum did not stimulate nitrogenase activity. Under oxygen-limited conditions A. hrasilcnxe and A. lipoferum were also shown to reduce nitrate to ammonia, which accumulated in the medium. Both species, including strains of A. hraxilenxe which do not possess a dissimilatory nitrite reductase (nir~) were also capable of reducing nitrous oxide to N2.