Mixed nitrifying bacteria culture under different temperature dropping strategies: Nitrification performance, activity, and community

In this study, the nitrification performance, metabolic activity, antioxidant enzyme activity as well as bacterial community of mixed nitrifying bacteria culture under different temperature dropping strategies [(#1) growth temperature kept at 20 degrees C; (#2) sharp1 decreased from 20 degrees C to 10 degrees C; (#3) growth at 20 degrees C for 6 days followed by sharp decrease to 10 degrees C; and (#4) gradual decreased from 20 degrees C to 10 degrees C] were evaluated. It was shown that acclimation at 20 degrees C for 6 days allowed to maintain better nitrification activity at 10 degrees 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). 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 degrees C exposure, and the nitrification performance was mainly limited by the nitrite oxidation capacity of NOB. Applying 6 days acclimation at 20 degrees C was beneficial for the mixed nitrifying bacteria culture to cope with low temperature (10 degrees C) stress, possibly due to the maintenance of metabolic activity, antioxidant enzyme activity stability as well as appropriate AOB/NOB ratio. (C) 2017 Elsevier Ltd. All rights reserved.