Effect of Dissolved Oxygen Tension on Production of Carotenoids, poly-β-hydroxybutyrate, Succinate Oxidase and Superoxide Dismutase by Azospirillum brasilense Cd Grown in Continuous Culture
Azospirillum brasilense strain Cd was grown in a medium containing NH4+ in a chemostat at a range of constant dissolved oxygen tensions (d.o.t.) (0·070–0·18 atm). Poly-β-hydroxybutyrate (up to 12% of the cell dry weight) increased under oxygen limitation and moderate dilution rate (D = 0·14 h−1). The highest carotenoid content was observed at high d.o.t. and dilution rates up to 0·12 h−1. The amount of protein varied with d.o.t. from 0·29 mg protein (mg dry wt)−1 at 0·007 atm to 0·54 mg at 0·18 atm. The yield efficiency and respiration rate were highest at low d.o.t. and decreased significantly at a d.o.t. of 0·18 atm. Succinate dehydrogenase and malate dehydrogenase activities increased 2·5-fold at 0·10-0·18 atm O2, whereas succinate oxidase and NADH oxidase activities increased consistently with increasing d.o.t. Azospirillum brasilense showed a low specific activity for catalase; the specific activity of superoxide dismutase increased sharply above 0·16 atm O2.
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Effect of Dissolved Oxygen Tension on Production of Carotenoids, poly-β-hydroxybutyrate, Succinate Oxidase and Superoxide Dismutase by Azospirillum brasilense Cd Grown in Continuous Culture