The effect of pH, inhibitors and nutrient deprivation on ammonia oxidation
N. europaea recovering from up to 7 days starvation showed no lag phase before nitrifying activity or growth could be measured. Cells starved for 1- 4 weeks had a lag phase of 20 - 40 min before activity. Cells starved for 0 - 7 d had no lag phase before growth. A lag phase before growth was initiated after 1 - 2 weeks starvation, which increased to 93 - 98 h after 6 weeks of starvation. Between 1 and 6 weeks starvation the nitrifying activity per ml of recovering cell suspension decreased significantly. N. europaea was also starved in continuous flow sand and soil columns. Cells recovering from starvation in sand columns resumed nitrifying growth and activity immediately at the same growth rate of cells initially inoculated into the column. Cells recovering from starvation in soil columns took longer to resume nitrifying activity than cells starved in sand. pH and nitrapyrin both had significant effects on nitrifying activity and the interaction between pH and nitrapyrin treatment was significant in the inhibition of both growth and activity. pH and PEX both significantly inhibited nitrifying activity but the interaction between pH and PEX was not significant. PEX completely inhibited growth at concentrations which only partially inhibited nitrifying activity. The optimum pH for nitrifying activity by N. europaea was between pH 8.5 and 9 and the optimum pH for growth was between 7.5 and 8.0. The optimum pH for activity increased as substrate concentration decreased. A previously published model quantifying the relationship between pH, substrate availability and ammonia oxidation (Quinlan, 1985) was tested. Data predicted using the model fitted experimental data when data from a limited pH range were used to calculate the coefficients (pH 7-9), but not when data from a wider range (6-9) were used.