It was shown that acclimation at 20°C for 6 days allowed better maintenance of nitrification activity at 10°C. The nitrite oxidation capacity of nitrifiers was significantly correlated with the relative light unit (RLU) (p<.05) and the fluctuation of superoxide dismutase (SOD) enzyme activity (p < .01). Samples with serial #3 showed the highest RLU levels and the least SOD enzyme fluctuation as compared to serials #2 and #4. Throughout the experimental period, Nitrosospira and Nitrosomonas as well as Nitrospira were identified as the predominant ammonia-oxidizing bacteria (AOB) and nitrate-oxidizing bacteria (NOB). The dynamic change of AOB/NOB ratios and nitrification activity in serials #2-#4 demonstrated that AOB recovered better than NOB with long-term 10°C exposure, and the nitrification performance was mainly limited by the nitrite oxidation capacity of NOB.
Scientists conclude that 6 days acclimation at 20°C was beneficial for the mixed nitrifying bacteria culture to cope with low temperature (10°C) stress, possibly due to the maintenance of metabolic activity, antioxidant enzyme activity stability, as well as appropriate AOB/NOB ratio.