英文摘要 | Municipal wastewater treatment plants have been regarded as the hotspot for the antibiotic resistance genes (ARGs), of which effluent has been one of the important sources for the spread of ARGs. However, the composition of intracellular ARGs (iARGs) and eARGs for the aquatic system replenished by reclaimed water and the key driven-factor for the iARGs and eARGs was not well-defined. Dissolved organic matter (DOM) are ubiquitous in the aquatic environment including the effluent of wastewater treatment plants, in which the composition is much complex, and plays an important role in the migration and transformation of various types of contaminants, such as heavy metals, organic pollutants, endocrine disrupters (EDC) and bacterial or pathogens.Besides, the relationship between DOM and the antibiotic resistance is still unclear. Hence, one river and one reservoir receiving effluent from the typical reclaimed water treatment plants were selected to take samples in dry and wet seasons. This study was aimed to clarify the fate and the abundance of iARGs and eARGs in the reclaimed water receiving water, and to identify the major influence factors for the iARGs and eARGs at different water-level period. Finally, the diversity and molecular characteristics of DOM for the samples were investigated. The detailed results are following:
(1) DOM for the Qinghe River and Shahe Reservoir were divided into five and four components, respectively, which were mainly composed of microbial endogenous metabolites with high bioavailability and low degree of humidity. But humic or humiclike matter may input into the water under the rainfall. There were six hydrogen-nuclear groups in the Sha river and Qing river which were detected by 1H-NMR spectra. The results showed that alkoxy groups and aliphatic hydroxyl groups was the main composition of DOM at dry season. While at wet season, carboxyl and aromatic cyclic hydronuclear groups were turned to the major structure for DOM. A positive correlation was found between DOM components (CH3, CH, CHO/N, HAr, Hp and CH-α) and relative abundance of pathogenic genes (p<0.05) in the Shahe Reservoir during the wet season.
(2) Bacterial 16S rRNA gene sequencing was applied to characterize bacterial community of iARGs and eARGs of Sha river and Qing river. Shannon index, Simpson index, Chao1 index and Ace index are calculated to explain the diversity and richness of the bacterial community. The results showed that the effluent would influence the composition of bacterial community of the receiving water at the dry season, while rainfall would increase the diversity of bacterial community. Protebacteria and Bacteroidetes are the two main bacteria at the phylum level in the Sha river and Qing river at different water-level period. Sha river and Qing river showed similarly predominant bacteria at phylum level at dry season and wet season, while they presented largely discrepancy at genus level.
(3) The abundance of iARGs and eARGs of Sha river and Qing river were measured by high-throughput qPCR, including 246 types of ARGs, 39 types of MGEs and 11 types of pathogenic genes. At dry season, the absolute abundance of iARGs and eARGs in Sha river were 2.83×106 copies/L ~ 5.27×1011 copies/L and 2.37×106 copies/L ~ 3.38×1012 copies/L, respectively, and those in Qing river were 8.34×105 copies/L ~ 5.78 × 1011 copies/L and 3.00 × 106 copies/L ~ 1.62 × 1013 copies/L ,respectively. When it turns into wet season, the absolute abundance of iARGs and eARGs in Sha river were 1.36×106 copies/L ~ 9.89×1012 copies/L and1.42×106 copies/L ~ 3.48×1010 copies/L, respectively, and those in Qing river were 1.20×106 copies/L ~ 9.27×1012 copies/L and 2.49×106 copies/L ~ 8.53×1011 copies/L copies/L,respectively. The abundance of iARGs in Sha river and Qing river were very similar,
while the abundance of eARGs in Qing river was much higher than Sha river, indicating that eARGs was an important and nonnegligible composition of antibiotic resistance in the aqueous environment. Herein, eARGs was the major composition of ARGs in dry season, but the principal composition of ARGs was iARGs at wet season. The correlation between ARGs (iARGs and eARGs) and bacteria community, MGEs and other environmental factors indicated that the main driven factors for ARGs would change under different water-level period. Finally, IS26 could be regarded as an indicator for eARGs at dry season, while it would be the marker for iARGs at wet season. Besides, we need to pay more attention to the pathogen from the effluent and its receiving water body because of the strong relationship between iARGs/eARGs and pathogene, if not so, ARGs would transfer into the pathogens and threat to the health of human. |