摘要

       最近观察到废水处理厂流出物中的游离 DNA 含有抗生素抗性基因 (ARG)，这可能有助于通过接收环境中的水平基因转移传播抗生素抗性。应用于废水和饮用水处理的技术膜系统位于“一个健康”方法的环境和人类相关方面之间的中心节点，被认为是抗生素抗性细菌的有效屏障。然而，没有评估它们对游离 DNA 中编码的 ARG 的渗透性，这可能是由于，例如，在特定处理过程中细菌死亡后游离 DNA 的释放。本研究探讨了通过技术膜过滤去除含有 ARG 的游离 DNA 的潜在和原理机制。测试了十种不同的膜，这些膜因电荷（中性和负性）和截留分子量（从微滤到反渗透的范围内）而异，用于去除游离 DNA（编码 ARG 和游离线性的纯超螺旋和线性化质粒）。不同水基质（蒸馏水和废水处理厂流出物）中具有更宽片段大小谱的染色体 DNA。我们的结果表明，截留分子量小于 5000Da 的膜（超滤、纳滤和反渗透）可以保留 ≥ 99.80% 的游离 DNA，包括纯质粒和不同大小的线性片段，而通常用于废水处理的微滤显示没有保留。尺寸排阻被确定为主要的保留机制。此外，膜的表面带电和膜表面上游离 DNA 的吸附在防止游离 DNA 渗透方面起着关键作用。目前，大多数应用的膜带负电荷以防止吸附天然有机物。在我们的研究中，由于游离 DNA 分子的排斥、吸附减少和膜表面堵塞减少，带负电荷的膜与中性膜相比显示出较低的游离 DNA 保留。因此，应用的膜可能不能作为自由 DNA 中编码的 ARG 的有效屏障，因为它只能根据截断的分子量进行预测。因此，在设计用于保留游离 DNA 的过滤系统时，需要仔细考虑膜的规格（截留分子量和电荷）。 

       It has recently been observed that cell-free DNA in the effluent of wastewater treatment plants contains antibiotic resistance genes (ARG), which may help spread antibiotic resistance through horizontal gene transfer in the receiving environment. The technical membrane system used in wastewater and drinking water treatment is at the central node between the environmental and human aspects of the "one healthy" approach, and is considered an effective barrier to antibiotic-resistant bacteria. However, they have not been evaluated for their permeability to the ARG encoded in cell-free DNA, which may be due to, for example, the release of cell-free DNA after the death of the bacteria during certain treatments. This study explored the potential and principle mechanism of removing free DNA containing ARG through technical membrane filtration. Ten different membranes were tested. These membranes vary in charge (neutral and negative) and molecular weight cut-off (ranging from microfiltration to reverse osmosis). They are used to remove free DNA (encoding ARG and free linear pure). Supercoiled and linearized plasmids). Chromosomal DNA with a wider fragment size spectrum in different water matrices (distilled water and wastewater treatment plant effluent). Our results show that membranes with a molecular weight cut-off of less than 5000 Da (ultrafiltration, nanofiltration, and reverse osmosis) can retain ≥99.80% of free DNA, including pure plasmids and linear fragments of different sizes, while microfiltration commonly used in wastewater treatment shows No reservations. Size exclusion was identified as the main retention mechanism. In addition, the surface charging of the membrane and the adsorption of free DNA on the membrane surface play a key role in preventing the penetration of free DNA. Currently, most of the applied membranes are negatively charged to prevent adsorption of natural organic matter. In our study, the negatively charged membranes showed lower free DNA retention than neutral membranes due to the repulsion of free DNA molecules, reduced adsorption, and reduced membrane surface blockage. Therefore, the applied membrane may not serve as an effective barrier to the ARG encoded in free DNA, because it can only be predicted based on the truncated molecular weight. Therefore, when designing a filtration system to retain free DNA, the specifications of the membrane (molecular weight cut-off and charge) need to be carefully considered.

https://www.sciencedirect.com/science/article/abs/pii/S0043135419306906