Deciphering of microbial community and antibiotic resistance genes to the selection pressures of antibiotic concentration in aerobic activated sludge reactors

Abstract

A high antibiotic concentration promotes the horizontal gene transfer (HGT) of antibiotic resistance genes (ARGs) in the wastewater while reducing the ARG abundance due to the production of resistance. However, the two-way effects of antibiotic concentration on the abundance of ARGs with different antibiotics are still lacking. Herein, the fate of ARGs and the corresponding composition of the microbial community (i.e., resistome and potential host bacteria for HGT) were investigated by adding two typical antibiotics (i.e., sulfadiazine, SDZ, and tetracycline hydrochloride, TC-HCl) under different concentrations. Results indicated that the initial antibiotic concentration for two antibiotics had different effects on the abundance of the corresponding ARGs (i.e., tet or sul); however, it was affected by the final antibiotic concentration, and a higher final antibiotic concentration would have a higher ARG abundance for both two antibiotic treatments. A higher initial antibiotic concentration would decrease the abundance but improve the diversity of the microbial community, resulting in the different biodegradation abilities of the corresponding antibiotic and subsequently affecting the resistome of microbial community, resulting in altering the abundance of ARGs (i.e., tet or sul). On the other hand, a higher final antibiotic concentration had a higher abundance of potential host bacteria, resulting in a higher abundance of ARGs (i.e., tet or sul). This study provides new insights into the mechanisms underlying the alteration of ARG abundance to the selection pressures of antibiotic concentration in aerobic activated sludge reactors.