Responses of activated sludge to quorum sensing inhibitor and antibiotic compound stress: Interactions among abundant-rare genera, functional genes, and antibiotic resistance genes

Quorum sensing inhibitors (QSIs) are considered as potentially promising alternatives to antibiotics, while their compound effects on activated sludge nitrification system are not known. This study aimed to investigate interactions among abundant-rare genera, functional genes, and antibiotic resistance genes (ARGs) under QSI (2(5H)-furanone) and antibiotic (ofloxacin) compound stress, their post-effect, and signaling molecule effect in activated sludge nitrification system. High concentrations compound stress inhibited nitrification and increased total nitrogen removal to 76.84%. Extracellular polymeric substances (EPS) content tended to decrease with increasing compound stress concentrations, and post-effect promoted EPS secretion, while signaling molecule effect promoted protein content more significantly. Microbial community structure of conditionally abundant taxa was significantly altered under compound stress. Conditionally rare or abundant taxa was the core taxa and showed abundant positive correlations with rare taxa. High concentrations compound stress promoted the proliferation of specific nitrogen removal functional genera such as Mesorhizobium, Hydrogenophaga and Rhodococcus, the expression of denitrification functional genes such as nosZ and napAB and occurrences of ARGs. Strong co-expressions were observed among specific ARGs subtypes and functional genes, especially with denitrification functional genes, and further promoted by post-effect and signaling molecule effect, which could enhance microbial resistance to stress. Microbial communities and ARGs had significant effects on nitrogen removal performance, and together explained 21.80% of change. This study emphasized contributions of component interactions in maintaining performance.