摘要
      污水处理厂是抗生素抗性基因的重要来源。由于无细胞形式的细胞外ARGs通过转化进行水平基因转移，因此人们越来越关注它们。然而，存在于污水处理厂活性污泥的胞外聚合物（EPS）中的胞外ARG的吸附形式的命运在很大程度上仍然未知。在此，使用定量聚合酶链反应对厌氧-缺氧-好氧（AAO）过程中的七个EPS相关ARG进行了定量。结果表明，EPS相关ARGs的绝对丰度比无细胞ARGs高0.69–4.52个对数。在AAO过程中，EPS相关ARG的丰度没有显著差异。在这些靶基因中，EPS相关的sul基因的丰度高于EPS相关的tet和bla基因。变形杆菌和拟杆菌是EPS相关ARGs的主要分泌菌，它们可能在细胞外ARGs增殖中发挥重要作用。此外，EPS相关ARGs的转化效率比无细胞ARGs高3.55–4.65个对数，表明EPS相关ARG具有更高的环境风险。这些发现促进了我们对EPS相关ARG的理解，并有助于WWTP中ARG的控制和风险评估。
Abstract
Wastewater treatment plants (WWTPs) are important sources of antibiotic resistance genes (ARGs). Increasing attention has been paid to extracellular ARGs in cell-free form due to their horizontal gene transfer via transformation. However, the fate of the adsorbed form of extracellular ARGs that exist in extracellular polymeric substances (EPS) of activated sludge in WWTP remains largely unknown. Herein, seven EPS-associated ARGs along the anaerobic-anoxic-aerobic (AAO) process were quantified using quantitative polymerase chain reaction. Results show that the absolute abundances of EPS-associated ARGs were 0.69–4.52 logs higher than those of cell-free ARGs. There was no significant difference in the abundances of EPS-associated ARGs along the AAO process. Among these target genes, the abundances of EPS-associated sul genes were higher than those of EPS-associated tet and bla genes. Proteobacteria and Bacteroidetes were identified as the major secretors of EPS-associated ARGs, and they may play an important role in the proliferation of extracellular ARGs. Moreover, the transformation efficiencies of EPS-associated ARGs were 3.55–4.65 logs higher than those of cell-free ARGs, indicating that EPS-associated ARGs have higher environmental risks. These findings have advanced our understanding of EPS-associated ARGs and are useful for the control and risk assessment of ARGs in WWTPs.

https://www.sciencedirect.com/science/article/abs/pii/S0048969721066535