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Inhibitory effect of cyanide on wastewater nitrification determined using SOUR and RNA-based gene-specific assays
Kapoor, V., M. Elk, X. Li, AND J. Santo-Domingo. Inhibitory effect of cyanide on wastewater nitrification determined using SOUR and RNA-based gene-specific assays. Letters in Applied Microbiology. Blackwell Publishing, Malden, MA, 63(2):155-161, (2016).
Nitrification is the first step of nitrogen removal is wastewater, and it is susceptible to inhibition by many industrial chemical. We looked at different concentration of cyanide and study their impact on nitrification using respiration rates and molecular assays.
The effect of CN- (CN-) on nitrification was examined with samples from nitrifying wastewater enrichments using two different approaches: by measuring substrate (ammonia) specific oxygen uptake rates (SOUR), and by using RT-qPCR to quantify the transcripts of functional genes involved in nitrification. The nitrifying bioreactor was operated as a continuous reactor with a 24 h hydraulic retention time. The samples were exposed in batch vessels to cyanide for a period of 12 h. The concentrations of CN- used in the batch assays were 0.03, 0.06, 0.1 and 1.0 mg/L. There was considerable decrease in SOUR with increasing dosages of CN-. A decrease of more than 50% in nitrification activity was observed at 0.1 mg/L CN-. Based on the RT-qPCR data, there was notable reduction in the transcript levels of amoA and hao for increasing CN- dosage, which corresponded well with the ammonia oxidation activity measured via SOUR. The inhibitory effect of cyanide may be attributed to the affinity of cyanide to bind ferric heme proteins, which disrupt protein structure and function. The correspondence between the relative expression of functional genes and SOUR shown in this study demonstrates the efficacy of RNA based function-specific assays for better understanding of the effect of toxic compounds on nitrification activity in wastewater.