Effect of Oxygen Concentration and Growth Rate on Glucose Metabolism, Poly- -hydroxybutyrate Biosynthesis and Respiration of Azotobacter beijerinckii

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Abstract
The effect of dissolved O2 concentration on glucose metabolism, poly-.beta.-hydroxybutyrate (PHB) synthesis and respiration of N2-fixing A. beijerinckii was investigated over a range of values spanning O2 limitation and sufficiency (N limitation) in continuous culture. The activities of the Entner-Doudoroff enzymes decreased with increasing O2 supply while glucose-6-phosphate dehydrogenase was unaffected; .beta.-ketothiolase and acetoacetyl-CoA reductase decreased more markedly, reflecting the fall in PHB content. The metabolic quotients for O2 and CO2 increased rapidly with increasing O2 supply, in keeping with the respiratory protection of nitrogenase. The specific activities of all these enzymes, and also of fructose-1,6-bisphosphate aldolase, increased with increasing dilution rate under either O2 or N limitation, except that both .beta.-ketothiolase and acetoacetyl-CoA reductase activities fell at the highest dilution rate (0.23 h-1) under O2 limitation. The role of the Entner-Doudoroff sequence as the major route of glucose metabolism in A. beijerinckii was unaffected by O2 concentration and growth rate.