Understanding pollutant-driven shifts of antibiotic resistome in activated sludge: A lab-scale study

Non-antibiotic pollutants have been identified as contributors to the development of antibiotic resistance across various environments. Wastewater treatment plants, recognized as hotspots for antibiotic resistance genes (ARGs), have received extensive attention regarding the mechanisms driving resistance changes in activated sludge. However, the specific impacts of heavy metals and aromatic organics-common pollutants in industrial wastewater-on the resistome of activated sludge, as well as the underlying mechanisms driving these effects, remain underexplored. In this study, we investigated the bacterial community and ARGs in activated sludge under the stress of three heavy metals and three aromatic organics. Our results revealed that both heavy metals and organics led to an increase in the total abundance of ARGs. Notably, the bacA and sul1 genes exhibited the highest abundance under both stress conditions, serving as indicative ARGs of the activated sludge resistome. The elevated ARG abundance was directly linked to shifts in the bacterial community induced by stress from heavy metals and aromatic organics, indicating an indirect co-selection of ARGs via metal resistance genes and aromatic degrading genes. Despite the overall increase in ARG abundance, the proportion of high-risk ARGs did not rise, suggesting that higher ARG abundance does not necessarily correlate with an elevated risk.