SUMMARY: The influence of dissolved oxygen concentration on the metabolism and respiration of growing NCTC 8017 was studied by means of a continuous-flow culture technique. Different dissolved oxygen tensions (equivalent partial pressures) were obtained by varying the partial pressure of oxygen in the gas phase. The respiration rate (oxygen uptake rate per unit mass organism) was independent of dissolved oxygen tensions above 10-15 mm. Hg when the culture was said to be in the ‘excess oxygen state’. With dissolved oxygen tensions below about 10 mm. Hg, the ‘limited oxygen state’ developed. In the transition to this state, complex oscillations in the dissolved oxygen tension occurred. The oscillations reflected alternate stimulation and inhibition of the respiration rate. A decrease in dissolved oxygen tension to below 5 mm. Hg immediately increased the respiration rate; an increase in dissolved oxygen tension from 5 to 10 mm. Hg immediately decreased the respiration rate. These effects formed part of the mechanism of the oscillations which could be sustained indefinitely. The oscillations in respiration rate occurred irrespective of change from pH 6·0 to 7·4 or whether growth was limited by glucose or ammonium supply. The pattern of oscillations in respiration rate varied with growth rate over the range 0·2-0·5 hr. It is suggested that decreasing the oxygen tension to about 5 mm. Hg acted like an uncoupler of oxidative phosphorylation.

In the excess oxygen state with excess glucose and growth limited by ammonium supply, the glucose carbon was largely accounted for as CO, pyruvate and organisms, irrespective of the pH value. Pyruvate was not accumulated when growth was glucose-limited. In the limited oxygen state, the glucose carbon was largely accounted for as: organisms, CO, 2:3-butanediol, ethanol, acetic acid, formic acid, lactic acid. The proportions of these fermentation products varied with oxygen supply, pH value and whether growth was ammonium-limited or glucose-limited.


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