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Oxygen regulation of nitrate uptake in denitrifying Pseudomonas aeruginosa

Oxygen had an immediate and reversible inhibitory effect on nitrate respiration by denitrifying cultures of Pseudomonas aeruginosa. Inhibition of nitrate utilization by oxygen appeared to be at the level of nitrate uptake, since nitrate reduction to nitrite in cell extracts was not affected by oxygen. The degree of oxygen inhibition was dependent on the concentration of oxygen, and increasing nitrate concentrations could not overcome the inhibition. The inhibitory effect of oxygen was maximal at approximately 0.2% oxygen saturation. The inhibition appeared to be specific for nitrate uptake. Nitrite uptake was not affected by these low levels of aeration, and nitrite reduction was only partially inhibited in the presence of oxygen. The regulation of nitrate respiration at the level of transport by oxygen may represent a major mechanism by which the entire denitrification pathway is regulated in P. aeruginosa.