title: Effect of oxygen and nitrate on nitrogen fixation and denitrification by Azospirillum brasilense grown in continuous culture.
abstract: Azospirillum brasilense was grown continuously at various levels of dissolved oxygen (O2) in a nitrogen-free medium containing malates as the carbon source. Steady-state cultures were established only at O2 concentrations less than 0.0150 atm (1 atm = 101.325 Pa) and rates of acetylene reduction (N2 fixation) and efficiencies of N2 fixation were maximal between 0.0050-0.0075 atm dissolved O2. These cultures appeared to be O2- or N2-limited. There was no evidence of a respiratory protective mechanism in this organism. Anaerobic denitrifying steady-state cultures were established with nitrate (NO3-) as the sole nitrogen source with no detectable N2 fixation. N2 fixation, but no denitrification, was observed when NO3- was decreased to 10 microgram N per millilitre at 0.003 atm dissolved O2. In samples removed from the culture vessel, either activity could be induced with a lag of approximately 120 min by incubation under appropriate conditions.
mesh_terms: D000114:Acetylene / Q000378:metabolism; D005030:Ethylenes / Q000378:metabolism; D008293:Malates / Q000378:metabolism; D009566:Nitrates / Q000378:metabolism*; D009586:Nitrogen Fixation / Q000187:drug effects*; D010100:Oxygen / Q000494:pharmacology*; D010944:Plants / Q000382:microbiology*; D012988:Soil Microbiology; D013139:Spirillum / Q000187:drug effects* / Q000378:metabolism
chemical_list: D005030:Ethylenes; D008293:Malates; D009566:Nitrates; D000114:Acetylene; D010100:Oxygen