Ecological effects of antibiotics on aquaculture ecosystems based on microbial community in sediments

Antibiotics are commonly used in aquaculture facilities during the production cycle, resulting in the gradual development of antibiotic adaptability with prolonged aquaculture histories. Three concentrations (0 (control), 10 mg/kg, and 1000 mg/kg) of each antibiotic (oxytetracycline (OTC), sulfadiazine (SD))were re-entered and were left with four months exposure in the aquaculture sediments of shrimp ponds with an approximately long-term drug application history (5, 15, and more than 30 years). In sediments with 5 (sediment A) and 30 years aquaculture histories (sediment C), microbial diversity (Chao1 Index and Shannon Index) had no significant change with the increasing SD or OTC concentration. In sediment with 15 years aquaculture history (sediment B), microbial diversity decreased significantly with increasing OTC concentration, but showed a tendency to first decrease and then increase with an increasing SD concentration. Meanwhile, both indices of microbial diversity in sediment A were significantly lower than that in sediment B and C. The dominating phyla in all samples were Proteobacteria, Chloroflexi, Firmicutes, Bacteroidetes, and Planctomycetes, while the top 5 genera included Sulfurovum, Methylophaga, Sulfurimonas, Thioalkalispira, and Desulfobulbus, whose relative abundance varied with aquaculture history and antibiotic concentration. The function profiles of the bacterial community (Kyoto Encyclopedia of Genes and Genomes) showed that three pathways of membrane transport, amino acid metabolism, and carbohydrate metabolism were inhibited in microcosms with antibiotics. These findings illustrated that microbial communities in sediment with 5 years aquaculture histories and 15 years aquaculture histories were more sensitive to antibiotics than the microbial community in sediment with 30 years aquaculture histories. And, microbial community in sediment gradually formed antibiotic resistance/tolerance profiles during the long-term antibiotic application.