Competition between oxygen and nitrate respirations in continuous culture of Pseudomonas aeruginosa performing aerobic denitrification

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Abstract
Continuous culture of P. aeruginosa was conducted with nitrate‐containing media under the dilution rates (D) of 0.026, 0.06, and 0.13/h and the dissolved oxygen concentrations (DO) of 0–2.2 mg/L. The bacterium performed simultaneous O2 and nitrate respiration in all of the systems studied. For each D, the (apparent) cell yield from glucose (YX/S) was lower at zero DO, but did not change substantially with non‐zero DO. In non‐zero DO systems, YX/S increased with increasing D, and when fit with a model considering cell death, gave the following parameters: maximum cell yield Y = 0.49, maintenance coefficient MS = 0.029 (/h), and cell decay constant kd = 0.014/h. The same model failed to describe the behaviors of zero‐DO systems, where neither glucose nor nitrate was limiting and the limiting factor(s) remained unknown. The cell yield from accepted electron (YX/e) was however relatively constant in all systems, and the energy yield per electron accepted via denitrification was estimated at ∼69% of that via O2 respiration. A closer examination revealed that increasing DO enhanced O2 respiration only at extremely low DO ( 2 was the preferred electron acceptor, the fraction of electrons accepted via denitrification increased with increasing D.

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