Mass-immigration shapes the antibiotic resistome of wastewater treatment plants

Abstract

Wastewater treatment plants (WWTPs) are the hotspots for the spread of antibiotic resistance genes (ARGs) into the environment. Nevertheless, a comprehensive assessment of the city-level and short-term daily variations of ARG surveillance is still lacking in WWTPs. Here, 285 ARGs and ten mobile gene elements (MGEs) were monitored in seven WWTPs in Xiamen via high-throughput qPCR (HT-qPCR) for seven days. The average daily load of ARGs to WWTPs was about 1.21 x 1020 copies/d, and a total of 1.44 x 1018 copies/d was discharged to the environment across the entire city. Interestingly, no daily variations were observed in ARG richness, abundance, and community composition. Stochastic processes were the main force determining the assembly of ARG communities, with their relative importance ranked in the order of influent (INF) > effluent (EFF) > activated sludge (AS). Further analyses indicated that bacteria and ARGs from upstream treatment units played an increasingly dominant role in shaping ARG communities in AS and EFF, respectively, suggesting the importance of mass-immigration of bacteria and ARGs from the source on ARG transport in wastewater treatment units. This emphasizes the need to revise the way we mitigate ARG contamination but focus on the source of ARGs in urban wastewater.