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

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 O 2 and nitrate respiration in all of the systems studied. For each D , the (apparent) cell yield from glucose ( Y X/S ) was lower at zero DO, but did not change substantially with non‐zero DO. In non‐zero DO systems, Y X/S increased with increasing D , and when fit with a model considering cell death, gave the following parameters: maximum cell yield Y   X/S m  = 0.49, maintenance coefficient M S  = 0.029 (/h), and cell decay constant k d  = 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 ( Y X/e ) was however relatively constant in all systems, and the energy yield per electron accepted via denitrification was estimated at ∼69% of that via O 2 respiration. A closer examination revealed that increasing DO enhanced O 2 respiration only at extremely low DO ( <0.05 mg/L), beyond which the increasing DO only slightly increased its weak inhibition on denitrification. While O 2 was the preferred electron acceptor, the fraction of electrons accepted via denitrification increased with increasing D . © 2006 Wiley Periodicals, Inc.