The fate and behavior mechanism of antibiotic resistance genes and microbial communities in anaerobic reactors treating oxytetracycline manufacturing wastewater

In this study, two parallel-operated expanded granular sludge bed (EGSB) reactors, one used to treat oxytetracycline (OTC) manufacturing wastewater with gradual increase of OTC concentration as experimental reactor and the other fed with the same wastewater without OTC as control reactor, were operated to investigate the behavior of antibiotics resistance genes (ARGs) and mobile genetic elements (MGEs) and their possible relationships with bacterial community among influent, sludge and effluent environments. Though the average absolute abundance of ARGs slightly decreased (0.26 - log), the ARGs’ relative abundance normalized to 16S-rRNA gene copy numbers showed a significant upward trend in effluent (2 multiples - increase) and the absolute and relative abundances both extremely increased in anaerobic sludge, indicating that anaerobic treatment process cannot reduce ARGs efficiently, inversely can increase the risk of ARGs through the proliferation of antibiotics resistance bacteria (ARB) under the suppression of OTC. MGEs, bacterial communities and OTC concentration mainly impacted the ARGs profiles, which contributed 88.4% to the variation of ARGs. The differences and correlations of hosts in influent, effluent and sludge were further confirmed by network analysis. Overall, this study enhanced the understanding of the prevalence and transfer of ARGs in OTC production effluents during anaerobic treatment.