SUMMARY: The effect of dissolved oxygen concentration on glucose metabolism, poly-β-hydroxybutyr-ate (PHB) synthesis and respiration of nitrogen-fixing was investigated over a range of values spanning oxygen limitation and sufficiency (nitrogen limitation) in continuous culture. The activities of the Entner-Doudoroff enzymes decreased with increasing oxygen supply while glucose-6-phosphate dehydrogenase was unaffected; β-ketothiolase and acetoacetyl-CoA reductase decreased more markedly, reflecting the fall in PHB content. The metabolic quotients for O and CO increased rapidly with increasing oxygen 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 oxygen or nitrogen limitation, except that both β-ketothiolase and acetoacetyl-CoA reductase activities fell at the highest dilution rate (0·23 h) under oxygen limitation. It was concluded that the role of the Entner-Doudoroff sequence as the major route of glucose metabolism in was unaffected by oxygen concentration and growth rate.


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