Study On The Spatial And Temporal Distribution Characteristics Of Antibiotic Resistance Genes In Mariculture Environment In Sansha Bay

Antibiotic residues can induce the development of antibiotic resistance genes(ARGs)in bacteria.ARGs have become emerging contaminants,which attracts more and more attention.ARGs are widely distributed in various environmental medium such as animal intestines,water and sediments,and eventually entered the human body through the food chain.ARGs can be transferred between parental and progeny of bacteria,even distantly related organisms through horizontal gene transfer(HGT).Once transferred into pathogens,ARGs will be a serious threat to human health.Aquaculture is one of the hardest hit areas for antibiotic use.Therefore,it is very important to carry out research on ARGs pollution in aquaculture environment.Sansha Bay,located in Ningde city,Fujian province,is an important base for Pseudosciaena crocea breeding and cage culture.According to the situation of mariculture in the bay,17 seawater samples and 8 surface sediment samples from were collected.The Real-time PCR was used to detect five types of 28 kinds of ARGs and one kind of integron genes intI1.This study aimed to investigate the occurrence of ARGs in Sansha bay,and explore the spatial and temporal distribution of abundance of ARGs in seawater and sediment.Next,the representative Pseudosciaena crocea cage culture in Sansha Bay was selected to sample the seawater and sediments once a month for one year to study the annual pattern of abundance of ARGs,and to evaluate the influence of cage culture on the variation of abundance and diversity of ARGs,The main results are as follows:(1)In Sansha Bay,11 kinds of ARGs were detected.They were sulfanilamide resistance genes(sul1,sul2),tetracycline resistance genes(tetA,tetB,tetC,tetG)and chloramphenicol resistance genes(cmlA,fexA),macrolide-lincosamide-streptogramin resistance genes(ermB)and quinolone resistance genes(qnrA,qnrC).Sulfanilamide and tetracycline resistant genes had the highest detection rate and absolute abundance and quinolone resistant genes had the lowest detection rate and absolute abundance.(2)Compared with Jiulong or Xiangjiang River,the absolute abundance of ARGs in the water of Sansha Bay was lower.In general,the total abundance of ARGs in water in winter was higher than that in summer.sul and tet resistance genes are the two most important resistance genes,accounting for an average of 94.32%in summer and 98.3 1%in winter.Season has great influence on the variety distribution of ARGs in water,and the dominant genes are different in different seasons.tetA,tetC,fexA,qnrA and qnrC mainly appeared in summer.In winter,sul2,tetG,cmlA and ermB were the dominant genes.Anthropogenic activity is the main factor of spatial variation of ARGs in water of Sansha Bay.(3)The absolute abundance of ARGs in the sediment of Sansha Bay was significantly higher than that in the water,in which the proportion of sulfonamide and tetracycline resistance genes decreased,while the proportion of macrolides and chloramphenicol resistance genes increased.In winter sediments,the abundance trend of ARGs showed obvious regional differences,and the diversity of ARGs was significantly different with that in water.In sediments,aquaculture is the main factor afrecting the distribution of ARGs.(4)In the water of Pseudosciaena crocea cage culture,the absolute abundance of ARGs in different months was significantly different,with the total abundance within the range of 1.42×103-1.36×105 copies/mL.From August to December of 2017,the detection quantity of sulfanilamide and tetracycline resistance genes was relatively high.From January to July of 2018,sulfanilamide resistance genes became the main dominant genes,and their absolute abundance was significantly higher than that of other ARGs.The abundance of ARGs in water is mainly affected by aquaculture activities.(5)In the sediment of Pseudosciaena crocea cage culture,the total abundance of ARGs ranged from 1.16×106-1.20×107 copies/g,which was significantly higher than that in water.Between August 2017 and January 201 8,sul1 and tetA were the dominant genes.From February 2018,the absolute abundance of ermB increased significantly,only lower than sull,becoming one of the major dominant genes.Seasonal variation had little effect on the abundance of ARGs in sediments,but had great effect on the diversity of ARGs.(6)The total abundance of ARGs in the water of Sansha Bay and Pseudosciaena crocea cage culture both had significant positive correlation with the abundance of intI1(p<0.01),suggesting that horizontal gene transfer(HGT)played an important role in ARGs transmission in Sansha Bay.In addition,the variety change of ARGs in the water of cage culture was maybe related to the decreased abundance of intl1.This study is helpful to learn the occurrence and distribution of ARGs in mariculture environment,and is useful to evaluate the marine ecological risk of ARGs.