Regulation of the tricarboxylic acid cycle and poly-beta-hydroxybutyrate metabolism in Azotobacter beijerinckii grown under nitrogen or oxygen limitation

J Gen Microbiol. 1976 Dec;97(2):303-12. doi: 10.1099/00221287-97-2-303.


Azotobacter beijerinckii was grown in ammonia-free glucose/mineral salts media in chemostat culture under oxygen or nitrogen limitation. Selected enzymes of the tricarboxylic acid cycle and poly-beta-hydroxybutyrate metabolism were monitored in relation to oxygen supply for both steady and transition states. Two dissolved oxygen concentrations were used for the nitrogen-limited steady state to investigate the possible effects of respiratory protection of nitrogenase on these enzymes. The levels of NADH oxidase, isocitrate dehydrogenase and 2-oxoglutarate dehydrogenase increased markedly on relaxation of oxygen limitation while pyruvate dehydrogenase and citrate synthase were relatively unaffected. beta-Ketothiolase and acetoacetyl-CoA reductase levels decreased as oxygen limitation was relaxed. Respiratory activity, as measured by the QO2 value, increased with oxygen supply rate. Imposition of oxygen limitation on a nitrogen-limited culture caused an immediate increase in the NADH/NAD ratio but this rapidly readjusted to its previous steady-state value. These changes are discussed in relation to respiratory protection of nitrogenase and poly-beta-hydroxybutyrate metabolism in A. beijerinckii.

MeSH terms

  • Acetyl-CoA C-Acetyltransferase / metabolism
  • Alcohol Oxidoreductases / metabolism
  • Azotobacter / enzymology
  • Azotobacter / metabolism*
  • Citrate (si)-Synthase / metabolism
  • Citric Acid Cycle*
  • Hydroxybutyrates / metabolism*
  • Isocitrate Dehydrogenase / metabolism
  • Ketoglutarate Dehydrogenase Complex / metabolism
  • NAD / metabolism
  • NADH, NADPH Oxidoreductases / metabolism
  • Nitrogen / metabolism*
  • Oxygen Consumption*
  • Pyruvate Dehydrogenase Complex / metabolism


  • Hydroxybutyrates
  • Pyruvate Dehydrogenase Complex
  • NAD
  • Alcohol Oxidoreductases
  • Isocitrate Dehydrogenase
  • Ketoglutarate Dehydrogenase Complex
  • NADH, NADPH Oxidoreductases
  • Acetyl-CoA C-Acetyltransferase
  • Citrate (si)-Synthase
  • Nitrogen