AMMONIA OXIDATION IN NITROSOMONAS AT NH3 CONCENTRATIONS NEAR K-M - EFFECTS OF PH AND TEMPERATURE

Nitrosomonas europaea from continuous pure cultures was incubated with 26.4 mu M NH3 (= 0.37 mg NH3-N l(-1)) at various NH4+ concentrations, pH values and temperatures. Measured rates of nitrite formation were significantly influenced by pH. Likewise unexpectedly, the maximum amm onia oxidation rate occurred between pH 6.7 and 7.0. Temperature had a n even stronger effect on the rate of ammonia oxidation than the avail ability of NH3. It is concluded that the assumption of a strict depend ence of the rate of ammonia oxidation on substrate concentration is an unjustified oversimplification. Among the mechanisms which could expl ain ammonium uptake and oxidation near or below pH 7.0, the formation of NO from HNO2 is considered.