Enrichment of Antibiotic Resistant Bacteria and Antibiotic Resistance Genes by Sulfamethoxazole in the Biological Treatment System of Mariculture Wastewater

Abstract

Although antibiotics are heavily used in mariculture, only a small portion of the added antibiotics is absorbed. Little is known about the response process of antibiotics, antibiotic resistant bacteria, and antibiotic resistance genes to antibiotic-containing wastewater entering a wastewater treatment system. In this study, an anoxic/aerobic moving bed biofilm reactor (A/O-MBBR) was used to treat marine aquaculture wastewater containing sulfamethoxazole (SMX). The antibiotics and resistance genes in the reactor were then evaluated under selective SMX pressure, and the changing abundance patterns and the response of microbial communities and cultivable resistant bacterial populations were further explored. The results show that with an influent SMX concentration of 500 μg ·L-1 and a hydraulic retention time of 8 h, SMX had a slight effect on the removal rate of NH4+-N and NO2--N, following which the performance gradually recovered. During this stage, SMX removal reached approximately 32%, with more than 78% of SMX removed from the hypoxic zone. The resistance gene was more significantly enriched in the hypoxic zone than in the aerobic zone. In the hypoxic zone, the absolute abundance of gene sul1 increased by 2.43 log, whereas that of gene sul2 increased by 1.71 log. In the region, the absolute abundance of sul1 increased by 1.17 log, whereas that of sul2 increased by 0.91 log. Resistant plate culture and high-throughput sequencing showed that the genus Pseudoalteromonas was the most dominant culturable resistant bacteria in the reactor. The genus Pseudomonas predominated in the uncultured resistant bacteria in the reactor. This study showed that marine aquaculture wastewater containing SMX promotes the enrichment of resistance genes, causing the abundance of some resistant bacteria to increase significantly.