Impact of Heavy Metals on Transcriptional and Physiological Activity of Nitrifying Bacteria

Heavy metals can inhibit nitrification, a key process for nitrogen removal in wastewater treatment. The transcriptional responses of amoA, hao, nirK, and norB were measured in conjunction with specific oxygen uptake rate (sOUR) for nitrifying enrichment cultures exposed to different metals (Ni­(II),...

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Published in:Environmental science & technology 2015-11, Vol.49 (22), p.13454-13462
Main Authors: Kapoor, Vikram, Li, Xuan, Elk, Michael, Chandran, Kartik, Impellitteri, Christopher A, Santo Domingo, Jorge W
Format: Article
Language:English
Subjects:
Ammonia - metabolism
Bacteria
Bacteria - drug effects
Bacteria - genetics
Bacteria - metabolism
Bioreactors - microbiology
Gene Expression Regulation, Bacterial
Genes
Heavy metals
Metals, Heavy - toxicity
Nitrification
Nitrogen
Nitrogen - metabolism
Up-Regulation
Waste Water - chemistry
Waste Water - microbiology
Water treatment
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Summary:Heavy metals can inhibit nitrification, a key process for nitrogen removal in wastewater treatment. The transcriptional responses of amoA, hao, nirK, and norB were measured in conjunction with specific oxygen uptake rate (sOUR) for nitrifying enrichment cultures exposed to different metals (Ni­(II), Zn­(II), Cd­(II), and Pb­(II)). There was significant decrease in sOUR with increasing concentrations for Ni­(II) (0.03–3 mg/L), Zn­(II) (0.1–10 mg/L), and Cd­(II) (0.03–1 mg/L) (p < 0.05). However, no considerable changes in sOUR were observed with Pb­(II) (1–100 mg/L), except at a dosage of 1000 mg/L causing 84% inhibition. Based on RT-qPCR data, the transcript levels of amoA and hao decreased when exposed to Ni­(II) dosages. Slight up-regulation of amoA, hao, and nirK (0.5–1.5-fold) occurred after exposure to 0.3–3 mg/L Zn­(II), although their expression decreased for 10 mg/L Zn­(II). With the exception of 1000 mg/L Pb­(II), stimulation of all genes occurred on Cd­(II) and Pb­(II) exposure. While overall the results show that RNA-based function-specific assays can be used as potential surrogates for measuring nitrification activity, the degree of inhibition inferred from sOUR and gene transcription is different. We suggest that variations in transcription of functional genes may supplement sOUR based assays as early warning indicators of upsets in nitrification.
ISSN:0013-936X
1520-5851
DOI:10.1021/acs.est.5b02748