Antibiotic resistance genes and mobile genetic elements in a rural river in Southeast China: Occurrence, seasonal variation and association with the antibiotics.

Human activities in rural areas, such as livestock farming, aquaculture, and rural domestic sewage discharge, may result in antibiotic resistance genes (ARGs) pollution in rural rivers. A systematic monitoring in different seasons was conducted in a typical agriculture-polluted river with Real-Time Quantitative PCR. A total of 11 ARGs and 2 related mobile genetic elements (MGEs) were detected at all sites with relative abundances of 6.9 × 10-0.2 copies/16S rRNA copies. Among them, sul1, sul2 and int1 were the dominant target genes in water samples. tetW, ermB, and floR were more abundant in November (the dry season), while other ARGs, MGEs and 16s rRNA were at a higher absolute abundance in warm seasons. There was less spatial variation of ARGs in the dry season than in the other two seasons. Furthermore, the relative abundance of ARGs was higher at sampling sites adjoining pollution sources. In addition, cluster analysis implied that ARGs in upstream sediments may be released into surface water and migrate downstream in the direction of river flow. There was no significant correlation between ARGs and their corresponding antibiotics. However, the total concentration of tetracycline was significantly correlated with the non-paired ARGs, including sul3, floR, and ermB. At the same time, heavy metals (Zn, Pb, Cd, Cr, As) and other environmental parameters (permanganate index, pH, DO) may apply selective pressure on the spread of ARGs, according to redundancy and Pearson's correlation analysis.