| Recently,the presence of antibiotic resistance genes(ARGs)in bacteria and even human pathogens has posed a serious threat to public health.ARGs have been prevalently detected in mariculture environment,and the mariculture sediment has been a hotspot of ARGs exchange.Up to now,high concentration of antibiotic residues is generally considered to be the primary cause for the elevated levels of ARGs in the environment.However,in mariculture environments where never used or stopped using antibiotics,high abundance of various ARGs can still exist for a long time.Therefore,besides antibiotics,the study of potential influencing factors in mariculture environments is necessary to comprehensivly understand and control the propagation of ARGs.Fishmeal is the one of main ingredients of fish feeds,and is released into mariculture sediments in large quantities.However,the influence of fishmeal on the ARGs and the effective technology to remove ARGs in mariculture sediments has never been reported.In this study,the abundance and diversity of ARGs in representative fishmeals were analyzed using high-throughput quantitative PCR and Illumina sequencing of 16S rRNA genes.The impacts of fishmeal on ARGs in mariculture sediments and the underlying mechanism were revealed.The feasibility of aquaculture water treatment technologies in ARG removal was also investigated in mariculture sediments.The main contents and conclusions of this paper are as follows:(1)Risk factors related to ARG dissemination was analyzed in fishmeal.The levels of antibiotics,ARGs,Mobile Genetic Elements(MGEs)and potential pathogenic bacteria(HPB)were investigated in 5 representative fishmeals.The concentration of antibiotics in fishmeal samples ranged from 16.3 to 54.0 ng/g,and the most dominant types were sulfonamides and fluoroquinolones.A total of 132 ARGs and 4 MGEs were detected potentially conferring resistance to almost all antibiotics.The range of relative ARG abundance was 6.9×10-3-4.1 ×10-1 copies/cell.The a-diversity indices of ARGs in chicken meal and meat and bone meal were higher than those in fishmeals,and the absolute abundance of ARGs was 1-2 orders of magnitude higher than those in fishmeals.In addition,25 different genera of potential HPB were detected in fishmeals,accounting for 5.0%-25.5%of the total microbial community,and the proportion of gram-negative bacteria in fishmeal was much higher than that of gram-positive bacteria.(2)The impact of fishmeal on sediment ARGs and the underlying mechanism was explored.Fishmeal significantly increased the abundance and diversity of ARGs in sediments,and changed the ARG profiles in sediments.The relative abundance of ARGs in the sediments added with 0.1%and 0.5%fishmeal both increased gradually,and the highest relative ARGs abundance observed on the 50th day were 2.4×102 and 4.1 ×10-2 copies/cell,respectively,which were 3-5 times higher than that in the initial sediment.The relative abundance of MGEs was higher than twice of that in initial sediment.Compared with the control group,fishmeal significantly increased the relative abundance of 16 ARGs(P<0.05).The mexF gene conferring resistance to chloramphenicol was the most enriched ARG,and the relative abundance of mexF was increased by 105-fold.Meanwhile,nutrient also significantly changed bacteria communities in sediment.Partial canonical correspoing analysis shows that environmental factors including total carbon,total nitrogen and pH,MGEs and bacterial communities together explained the 92.42%of the total ARG shifts.Bacterial community was the primary contributor to the overall ARG changes,contributing to 44.97%of the total variation.Mantel test based on Bray-Curtis distance showed that there was a significant correlation between sediment ARGs and bacterial communities(P<0.05).Therefore,bacterial communities induced by nutrients in fishmeal were the main driving force for ARGs in mariculture sediment.(3)The combined impacts of fishmeal and antibiotic on mariculture sediment ARGs was analyzed.Compared with microcosms added with only tetracycline,the ARG abundance in the sediments with the combination of fishmeal and tetracycline was higher.The results of principal coordinate analysis(PcoA)showed that both the profiles of ARGs and the composition of microbial community were clustered according to whether fishmeal was added.Mantel test based on Bray-Curtis distance showed that sediment ARGs was significantly correlated with bacterial community(r2=0.4983,P<0.05).The results of partial least squares path model showed that tetracycline had negative effects on bacterial community and ARGs in sediment samples.No significant correlation was observed between the concentration of tetracycline and the MGE abundances.The physicochemical properties of sediments including total carbon,total nitrogen and pH,had a significant negative direct influence on microbial community(P<0.05),and a significant positive direct influence on ARGs.Microbial community structure has the most positive influence on sediment ARGs.In addition,MGEs is also an important factor of sediment resistance change,but weaker than bacterial community.Therefore,microbial community structure is the main driving force for sediment ARGs,and the MGEs may also partially explain the increase of ARGs.(4)The feasibility of aquaculture water treatment technologies in ARG removal was investigated in mariculture sediments.In the first 14 days of the experiment,H2O2 effectively reduced the overall abundance of ARGs.However,the abundances of sediment ARGs were still enriched after 14 days.Aeration has no obvious control effect on ARGs during the whole experiment.The highest relative abundance of ARGs in H2O2 group,aerated group and fishmeal group were 0.045,0.0508 and 0.0509 copies/16S rRNA gene,respectively.H2O2 can reduce the abundance of MGEs significantly after adding fishmeal.Pearson's correlation suggested that there is a significant correlation between ARGs and MGEs(P<0.05),so H2O2 may reduce the relative abundance of ARGs in sediments by reducing the occurrence frequency of horizontal transfer.The results showed that the H2O2 had a better effect on the removal of ARGs,and the processing period had a great influence on the removal effect.The excessive treatment would lead to the increase in ARG abundance.In conclusion,this study confirmed that fishmeal itself is an important reservoir for ARGs.The fishmeal application significantly increased the abundance and diversity of ARGs in sediments,which is significantly correlated with the microbial communities induced by the nutrients in fishmeal.Fishmeal plays a more important role in the propagation of ARG in sediments than tetracycline.Hydrogen peroxide processing is effective to reduce sediment ARGs.The results provide an important theoretical basis for the research on the source,transmission mechanism,abundance prediction and risk assessment of ARGs in mariculture environment. 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