Use of Functional Gene Expression and Respirometry to Study Wastewater Nitrification Activity after Exposure to Low Doses of Copper
Citation:
Kapoor, V., X. Li, C. Impellitteri, K. Chandran, AND J. Santodomingo. Use of Functional Gene Expression and Respirometry to Study Wastewater Nitrification Activity after Exposure to Low Doses of Copper. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH. Ecomed Verlagsgesellschaft AG, Landsberg, Germany, 23(7):6443-6450, (2016).
Impact/Purpose:
The results from this study validate the use of molecular methods combined with conventional nitrification inhibition assays to better evaluate the response of wastewater nitrifying systems to the presence of heavy metals.
Description:
Biological nitrogen removal (BNR) is performed by autotrophic nitrification, which has been shown to be sensitive to the presence of heavy metals in wastewater treatment plants (WWTPs). In this research, the effect of copper on the relative expression of functional genes involved in redox nitrogen transformations were examined in nitrifying enrichment cultures. The nitrifying bioreactor was operated as a continuous reactor with a hydraulic retention time of 1 day. The cells were exposed in batch vessels to copper dosages ranging from 0.1 to 10 mg/L for a period of 12 h under starving conditions. Based on the RT-qPCR data, there were no considerable changes in the transcript levels of amoA, hao, nirK and norB, which correlated well with the ammonia oxidation activity measured via specific oxygen uptake rate (sOUR). Sequencing analysis of clone libraries indicated that amoA clones were most closely related to the Nitrosomonas group and that multiple AOB populations (i.e., <97% sequence identity) co-existed in the nitrifying bioreactor. The presence of different nitrifying bacteria was also detected via sequencing of hao and nirK clone libraries. Moreover, 16S rRNA gene next-generation sequencing showed that Nitrosomonas-like populations represented 60-70 % of the bacterial community, while other nitrifiers represented <10 %. The lack of nitrification inhibition by copper may be attributed to the role of copper as cofactor for ammonia monooxygenase. Overall, these results validate the use of molecular methods combined with conventional nitrification inhibition assays to better evaluate the response of wastewater nitrifying systems to the presence of heavy metals.
