The Study Of The Influence On Macroalgae Restoration To Microbial Community And Antibiotic Resistance Genes In Mariculture Sediment

The widespread use of antibiotics has caused the expression of considerable resistant bacteria and antibiotic resistance genes?ARGs?in maricultural environment.In recent years,the integrated aquaculture model in which farmed organisms and seaweed co-cultivation has been widely adopted because of the advantages of improving aquaculture water quality and aquaculture biological quality.At present,there has rarely been reported on the distribution,migration and transformation characteristics of ARGs in cultured sediments caused by the combined effect of seaweed and antibiotics in aquaculture.Thus,this study used seaweed to improve the water quality of aquaculture,and focused on the study of the effect of different seaweeds and oxytetracycline?OTC?on the microbial community structure,enrichment and transformation of ARGs in sediments.The main contents are as follows:1.Effect of different types of seaweeds and coexistence with OTC pressure on the microbial community structure and ARGs in the sedimentsThree types of seaweeds?Ulva fasciata,Codium cylindricum and Ishige okamurai,12g/L?were co-cultured with clam cultured sediment under 0 and 500?g/L OTC pressure for one month,respectively.Results showed that the most efficient removal rates of NO₃^--N?58.27±4.40%?and PO₄^3--P?56.87±5.81%?occurred in the system Codium cylindricum and Ulva fasciata both with OTC pressure achieved,respectively.Metagenomic sequencing results demonstrated that the largest phylum was all Proteobacteria in the sediments.The presence of seaweeds caused a significant increase of the relative abundance of Acidobacteria,while the seaweed coexistence with OTC pressure significantly promoted the relative abundance of Proteobacteria and Bacteroidetes.Besides,the relative abundance of Actinobacteria,Planctomycetes and Cyanobacteria significantly declined in the presence of seaweed and OTC pressure.A total of 257 ARGs subtypes detected in sediments,although there was no significant change in the total ARGs abundance,some of different ARGs subtypes had significant changes,such as CeoA,CeoB,MexF,tetPB and so on.Quantitative PCR?qPCR?analysis of the gene numbers of typical tetracycline resistance genes?TRGs??otrA,tetT,tetPB,tetO,tetM,tetW?found that only the absolute gene numbers of tetPB decreased significantly with the presence of Ishige okamurai.2.Effect of different densities of Ulva fasciata and various OTC concentrations on the microbial community structure and ARGs in the sedimentsThe fresh clam cultured sediment was co-cultured with different densities?0,5 and12g/L?of Ulva fasciata and different OTC concentrations?0,10,100 and 500?g/L?for three months.The removal rates of NO₃^--N?69.33±9.12%?and PO₄^3--P?61.02±3.54%?were both the highest in the presence of Ulva fasciata?12g/L?and OTC?500?g/L?.The metagenomic sequencing results showed that the abundance of Proteobacteria increased significantly with the increase of Ulva fasciata density,while the relative abundance of Firmicutes,Nitrospirae,Bacteroidetes decreased significantly with the influent of different OTC concentrations.A total of 223 ARGs subtypes were detected in sediments,higher density of Ulva fasciata,greater relative abundance of peptide type of ARGs.The increase of OTC stress enhanced the enrichment of peptides and MLS types ARGs.The results of qPCR indicated that different densities of Ulva fasciata significantly reduced the genes number of tetT,tetW and otrA,but promoted tetO and tetM gene numbers.Additionally,the presence of lower concentrations of OTC?10,100?g/L?had much more significant promotion for these TRGs than the highest OTC concentration?500?g/L?.