Marine Heterotrophic Nitrification–Aerobic Denitrification Process Treating Mariculture Wastewater: Microbiome and Resistome Responses to Multiantibiotic Stresses

Efficient treatment of mariculture wastewater is essential to the sustainable development of the mariculture industry, yet a high salinity and multiple antibiotics contained therein pose a serious challenge to biological treatment. In this study, marine heterotrophic nitrification–aerobic denitrification (MHNAD) bacteria were successfully augmented for mariculture wastewater treatment, and their multiantibiotic (i.e., ampicillin-tetracycline-sulfamethoxazole (ATS)) resistance mechanisms were deciphered through the co-occurrence patterns of microbiome and resistome. Up to an ATS dose of 36 mg·L–1, MHNAD bacteria exhibited a strong antibiotic resistance, achieving high organic and nitrogen removal efficiencies of 95.2 and 100%, respectively. Meanwhile, more extracellular polymeric substances were produced to enhance the bacterial resistance to antibiotics. The MHNAD genus, Klebsiella, invariably dominated the bioreactor (mean relative abundance of 34.1%) and mainly accounted for pollutant removals. The absolute abundance of total antibiotic resistance genes increased by 21.7 folds at an ATS dose of 72 mg·L–1, as compared to that without ATS. The abundance of sul1, tetQ, or intI1 was positively correlated with the ATS dose, and Klebsiella was strongly correlated with sul1, tetQ, tetX, and blaTEM. This study proposes a novel process for mariculture wastewater treatment through augmentation of MHNAD bacteria under multiantibiotic stresses.