Antibiotic resistance genes (ARGs) are globally prevalent in mariculture sediment, and their presence is an issue of concern in the context of antibiotic use. Although large amounts of fishmeal have been released into the sediment, the role of fishmeal in ARG dissemination remains unclear. In this study, high-throughput ARG profiles in representative fishmeal products and the impact of fishmeal on the sediment resistome were investigated. A total of 132 unique ARGs and 4 mobile genetic elements (MGEs) were detected in five fishmeal products. ARG abundance and diversity in the mariculture microcosm sediment were significantly increased by the addition of fishmeal, and trends in ARG patterns correlated with the resident bacterial community in sediment (P < 0.05). After DNase treatment of fishmeal removed 84.3% of total ARGs, the remaining nutrients in fishmeal increased the relative abundance but not the diversity of ARGs in microcosm sediment. Our study has revealed for the first time that fishmeal itself is a major reservoir for ARGs, and the shift in the bacterial community induced by the nutrients in fishmeal is the main driver shaping the resistome in mariculture microcosm sediment. Our findings caution against the previously unperceived risk of ARG propagation in fishmeal-receiving ecosystems.

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BACKGROUND: To accelerate direct interspecies electron transfer (DIET), magnetite is supplemented in anaerobic activated sludge (AS). However, it is usually reduced by dissimilatory iron reducing bacteria (DIRB). Therefore, an AS system supplemented with submicron magnetite particles (Fe 3 O 4 /AS) in an up-flow microaerobic sludge reactor was established, aiming to remove tribromophenol (TBP) efficiently and alleviate the magnetite dissolution.RESULTS: Under microaerobic condition (DO, 0.6 mg L −1 ), the efficiencies of removal of COD, TBP, and methane production in Fe 3 O 4 /AS system were, respectively, 14.3%, 16.7%, and 27.2% higher than those of the AS system. Correspondingly, the dehydrogenase (DHA) and Coenzyme F 420 (CoF 420 ) activities were separately 1.38-fold and 1.41-fold enhanced. The enhanced biodegradation was via potential DIET, as visualized by microbes and magnetite particles, Geobacter enrichment and c-type cytochromes (c-Cyts) increasement. Notably, magnetite majorly maintained an intact structure. In effluents, the Fe(II) concentrations were maintained at less than 10 mg L −1 under microaerobic conditions, far less than the amount under anaerobic conditions, which might be due to the in situ redox cycle of Fe(III)-reduction and Fe(II)-reoxidation. CONCLUSION: Significant enhancements in removal efficiencies of TBP and COD and methanogenesis were demonstrated in a Fe3 O 4 /AS system, indicating intrinsically faster electron transfer via electrical conduction. Putative oxidation of dissolved Fe(II) in situ occurred in microaerobic environments, which could protect magnetite in the system without extra magnetite supplementation. Industry increase of COD (1000-2000 mg L −1 ) and TBP (5-20 mg L −1 ) at 0.6 mg L −1 DO concentration. Anaerobic, microaerobic and aerobic conditions were introduced to evaluate the effect on TBP and COD removal and methanogenesis by different DO concentrations J Chem Technol Biotechnol 2019; 94: 730-738

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