摘要
      抗生素耐药性基因（ARGs），尤其是最后手段ARGs，作为地下水中新出现的环境污染物，正受到广泛关注。然而，它们普遍存在的细胞内和细胞外模式以及地下水中的细菌来源仍不清楚。本文收集了天津市的地下水样本，并根据细胞内ARGs（iARGs）和细胞外ARGs的特征，以及常驻细菌群落和细胞外DNA（eDNA）释放细菌群落进行了表征。定量实时PCR分析显示，eARGs比iARGs表现出更少的亚型，并且通常显示出比相应的iARGs更低的检测频率。同样，LARG的检测频率低于普通ARG，但它们之间的总丰度没有显著差异。基因vanA和blaVIM是观察到的显性LARG，而aadA是观察到与细菌内部或外部位置无关的常见ARG。此外，前10个门在主要的eDNA释放细菌和主要的驻留细菌之间显示出很大的差异。变形杆菌是主要的常驻细菌门，同时也是地下水中eDNA的主要来源。尽管在常驻细菌中只占丰度的一小部分，但令人惊讶的是，放线菌属、不动杆菌属和Chloroflex占了eDNA释放的大部分。持久性ARGs、驻留细菌和eDNA释放细菌之间的共存模式表明，占主导地位的常见iARG-aadA和细胞内LARG-blaVIM和vanA与甲基杆菌_Methylorubum和Shewanella具有显著的正相关。同时，主要的细胞外LARG blaVIM可能由属于至少五个属的细菌释放，包括Ellin6067、双歧杆菌、Blautia、Veillonella和脱氯单胞菌。总之，这项研究的结果扩展了我们对ARGs及其细菌来源在地下水中分布的理解，并表明地下水中的LARGs污染严重，对公众健康构成潜在风险。
Abstract
Antibiotic resistance genes (ARGs), especially last-resort ARGs (LARGs), are receiving extensive attention as emerging environmental contaminants in groundwater. However, their prevalent intracellular and extracellular patterns and bacterial sources in groundwater remain unclear. Herein, groundwater samples were collected in Tianjin, and characterized based on the profiles of intracellular ARGs (iARGs) and extracellular ARGs (eARGs), as well as the resident bacterial communities and extracellular DNA (eDNA)-releasing bacterial communities. The quantitative real-time PCR assays showed that eARGs presented fewer subtypes than iARGs and generally displayed lower detection frequencies than the corresponding iARGs. Similarly, LARGs exhibited lower detection frequencies than common ARGs, but the total abundance showed no significant differences between them. Genes vanA and blaVIM were the observed dominant LARGs, and aadA was the observed common ARG independent of location inside or outside the bacteria. Furthermore, the top 10 phyla showed much difference between the main eDNA-releasing bacteria and the dominant resident bacteria. Proteobacteria was the predominant resident bacterial phyla while dominating the source of eDNA in groundwater. Despite representing a minor portion of the abundance in the resident bacteria, Actinobacteriota, Acidobacteriota, and Chloroflex surprisingly accounted for a large majority of eDNA release. Co-occurrence patterns among persistent ARGs, the resident bacteria, and eDNA-releasing bacteria revealed that the dominant common iARG aadA and intracellular LARGs blaVIM and vanA had significant positive correlations with Methylobacterium_Methylorubrum and Shewanella. Meanwhile, the dominant extracellular LARG blaVIM may be released by bacteria belonging to at least five genera, including Ellin6067, Bifidobacterium, Blautia, Veillonella, and Dechloromonas. Collectively, the findings of this study extend our understanding regarding the distribution of ARGs and their bacterial sources in groundwater, and indicate the serious pollution of LARGs in groundwater, which poses potential risks to public health.

https://www.sciencedirect.com/science/article/abs/pii/S0269749122007552