Effects of oxygen on each step of denitrification on Pseudomonas nautica

Studies on the effect of oxygen on denitrification have shown that denitrification on Pseudomonas nautica 617 can take place in the presence of oxygen. The enzymes associated with denitrification are affected differently with respect to oxygen concentration. Nitrate reductase was less sensitive toward oxygen than nitrite and nitrous oxide reductases. Nitrate reductase activity was completely blocked at an oxygen concentration greater than 4.05 mg/L, compared with 2.15 and 0.25 mg/L for nitrite and nitrous oxide reductases, respectively. After an aerobic–anaerobic shift, nitrate reductase activity remained unchanged whereas the rate of nitrite reductase activity rose to a value only 20% that of the original rate.Key words: denitrification, oxygen, Pseudomonas.