U.S. Environmental Protection Agency, Office of Research and Development, Cincinnati, Ohio 45268, United States.
Pegasus Technical Services, Inc., Cincinnati, Ohio 45268, United States.
Environ Sci Technol. 2015 Nov 17;49(22):13454-62. doi: 10.1021/acs.est.5b02748. Epub 2015 Nov 5.
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.
重金属会抑制硝化作用，而硝化作用是废水处理中氮去除的关键过程。本研究采用实时荧光定量 PCR（RT-qPCR）技术，测定了不同浓度重金属（Ni(II)、Zn(II)、Cd(II) 和 Pb(II)）对氨氧化菌 amoA、羟胺氧化还原酶 hao、亚硝酸盐氧化还原酶 nirK 和硝酸盐还原酶 norB 基因转录的影响，并结合比耗氧速率（specific oxygen uptake rate，sOUR）对硝化富集培养物的响应。结果表明，随着 Ni(II)（0.03-3 mg/L）、Zn(II)（0.1-10 mg/L）和 Cd(II)（0.03-1 mg/L）浓度的增加，sOUR 显著降低（p < 0.05）。然而，Pb(II)（1-100 mg/L）浓度对 sOUR 没有明显影响，除了 1000 mg/L 浓度导致 84%的抑制。根据 RT-qPCR 数据，amoA 和 hao 的转录水平在暴露于 Ni(II)时降低。当暴露于 0.3-3 mg/L 的 Zn(II)时，amoA、hao 和 nirK 的表达水平略有上调（0.5-1.5 倍），尽管 10 mg/L 的 Zn(II)使它们的表达水平降低。除了 1000 mg/L 的 Pb(II)，Cd(II)和 Pb(II)的暴露均会刺激所有基因的表达。虽然总体结果表明，基于 RNA 的功能特定测定可以用作测量硝化活性的潜在替代物，但从 sOUR 和基因转录推断的抑制程度不同。我们建议，功能基因转录的变化可能会补充基于 sOUR 的测定，作为硝化作用失调的早期预警指标。
