ACTA Scientiarum Naturalium Universitatis Pekinensis
Variations of 4 Antibiotic Resistance Genes in a Sewage Treatment Plant
BAO Yingyu1, XIE Hui2, CHEN Lüjun2, WEN Donghui1,†
1. College of Environmental Sciences and Engineering, Peking University, Beijing 100871; 2. School of Environment, Tsinghua University, Beijing 100084; † Corresponding author, E-mail: dhwen@pku.edu.cn
Abstract In order to understand the variations of antibiotic resistance genes (ARGS) in sewage treatment plants (STPS), the distribution and removal efficiencies of 4 subtypes of intracellular ARGS (sulii, ermb, tetc and blapse-1) and class I integron integrase gene (inti1) in a middle-scale STP in Hebei Province were detected by PCR and realtime fluorescent quantitative PCR (QPCR). 4 ARGS and inti1 were found in all water samples and 1.26–2.30 orders of magnitude of ARGS were removed by the STP. Correlation analysis showed that inti1 and water quality factors including ph, COD, and NH3-N might affect the distribution and diffusion of tetc, ermb, and blapse-1. The final effluent of a STP may promote the spread of ARGS in surface water system. Keywords antibiotic resistance genes (ARGS); sewage treatment plants (STPS); A2/O process; real-time fluorescence quantitative PCR (QPCR)
由于环境选择压力(抗生素、重金属等)的存在,抗生素抗性基因(antibiotic resistance genes, ARGS)得以迅速在环境中产生与传播[1]。与化学污染物不同, ARGS具有遗传复制、水平转移(horizontal gene transfer, HGT)等生物学特性[2–3], 一旦进入环境就很难控制和消除。因此, 近年来ARGS成为备受瞩目的一种新型污染物。研究表明, ARGS在常规的城镇污水处理厂进、出水中普遍存在[4–5]。城镇污
水处理系统中的抗生素、重金属、可移动遗传元件(mobile genetic elements, MGES)和微生物等可能对ARGS的形成、水平转移和扩散起到促进作用[6]。因此, 对城镇污水处理厂中ARGS赋存特征和去除效果展开研究十分必要。
京津冀地区是我国北方经济的重要核心区, 人口密集, 是抗生素排放强度较大的区域之一[7], 存在潜在的ARGS污染风险。本研究选取京津冀地区
Fig. 1
图2(b)显示目标基因在污水处理系统各单元中的相对丰度(即目标基因与16S RDNA拷贝数之比)。对比图 2(a)与(b)可知, ARGS及 inti1在绝对丰度和相对丰度上的变化趋势不同。这是由单位体积水样的微生物量差异引起的[11], 仅关注绝对丰度无法体现 ARGS在微生物基因组中的占比情况, 因此对ARGS及 inti1的相对丰度进行分析十分必要。
总进水中各目标基因的相对丰度在10−5~10−2之间, 与绝对丰度结果一致, 进水中相对丰度最高的为ermb。ermb, tetc, blapse-1 与 inti1的相对丰度变化趋势大致相同: 经过细格栅和旋流沉砂池、A2/O各处理阶段, 上述基因在微生物群落基因组中的占比逐渐下降; 经过二次沉淀、絮凝沉淀和消毒后, 相对丰度呈上升趋势。sulii相对丰度的变化趋势与上述基因有较大的差异。在A2/O的厌氧区中, sulii相对丰度升高。经过二次沉淀和絮凝沉淀, sulii相对丰度呈上升趋势。消毒处理后, sulii 相对丰度降低, 但仍显著高于总进水。
总出水中, 目标基因的相对丰度分布在6.76× 10−5~5.71×10−2之间, sulii, tetc 和 inti1的相对丰度高于进水, 说明污水处理后, 这几类基因在微生物
Table 3
Correlation between the target genes’ absolute abundances and water quality factors
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