| In recent years,with the abuse of antibiotics in the breeding and other fields,the residue of antibiotics in the environment is getting worse.Antibiotics can induce the emergence of antibiotic resistance genes(ARGs),and ARGs can be transferred horizontally in various microbial communities through mobile genetic elements(MGEs),which accelerates the spread and proliferation of antibiotic resistance,the status of ARGs pollution in the environment has become the focus of research.Hainan Mangrove forest is one of the most abundant area of mangrove species in China.Antibiotics emissions from aquaculture in the region are widespread.The mangrove area is subject to double pressure from the ocean and land in this process,the problem cannot be underestimated.Sediment as an important environmental medium is an ideal place for the accumulation of pollutants.Therefore,this study selected 13 transects of Hainan Mangrove cover area for sediment samples collection,and samples of each transects were collected in high,middle and low tide level.Then,liquid chromatography-electrospray ionization tandem mass spectrometry(LC-MS/MS)and high-throughput quantitative polymerase chain reaction(HT-PCR)were used to quantify four types of antibiotics(sulfonamides,fluoroquinolones,tetracyclines,chloramphenicols)and 283 ARGs,12 MGEs,respectively;high-throughput sequencing was used to study microbial diversity.Through the correlation analysis of antibiotics,ARGs and microorganisms,the possible sources and potential hosts of ARGs were obtained.This study is the first comprehensive investigation of antibiotics and ARGs in sediments of Hainan Mangrove area,which provides basic data for the status of antibiotics and ARGs pollution in this area,and provides a scientific basis for the protection and management of Hainan Mangrove ecosystem.The main findings are as follows:(1)4 types of 21 antibiotics were detected in the study area.The concentration of antibiotics in different transects ranged from 0.43 to 52.17 μg·kg-1,of which the concentration of Danchang(DC)in Bamen Bay was the highest and the lowest in Caiqiao(CQ).Results showed significant differences in antibiotic concentrations between different sampling transects.Antibiotic concentrations are at a relatively low level compared to similar studies.Among the 4 types of antibiotics,the average concentration of sulfonamides was the highest(8.44μg·kg-1)、and the average concentration of Chloramphenicols was the lowest(0.55 μg·kg-1).The detection of these antibiotics indicated that the study area has been disturbed by human activity.(2)A total of 179 ARGs were detected in the study area.The detection rate of vancomycin resistance gene vanXD and MLSB resistance gene vatE-01 was 100%.The absolute abundance of ARGs ranged from 8.30×107～6.88×08 copies·g-1,and the normalized abundance was 0.05～0.14 copies·cell-1,which was higher than that of similar studies,and the spatial distribution of antibiotics in these sampling transects has difference.The multidrug resistance genes account for the highest proportion(69.02%),which indicated that the sources of ARGs in sediments of Hainan Mangrove was very complicated.The ARGs in sediments of Hainan Mangrove are weakly correlated with antibiotics,but have a significant positive correlation with MGEs,indicating that the high level of ARGs is related to its own self-enhancement.(3)The bacterial diversity in sediments of Hainan Mangrove area was investigated by the high-throughput sequencing,a total of 78 phyla,220 classes,335 orders,383 families,and 718 genera were identified,this area has abundant microbial resources.The dominant bacteria at genus level were Bacillus,Clostridium,Desulfococcus and Enterococcus.Correlation analysis between ARGs and microorganisms revealed that there was a significant positive correlation between 138 bacterial genera and some ARGs,indicating that the host relationship of ARGs in the study area is very complicated.Chthoniobacter,Flavisolibacter,Forvivibrio,Kaistia,Methanomethylovorans,Methanosphaera,Moryella,MSBL3,Perlucidibaca,Zhouia,etc.are the main potential hosts of ARGs in sediments of Hainan Mangrove,and these bacteria are important participants in the biogeochemical cycles,then,ARGs pollution in this area should be taken seriously. |
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