Distribution And Transmission Mechanism Of Antibiotic Resistance Genes In Mangroves And Estuaries

Mangrove ecosystem enjoys the title of "coastal guardian",because it combines the biological characteristics of terrestrial ecology and Marine ecology,making mangrove become the natural ecological research center.Estuarine ecosystem is an important aggregation zone where the four circles of the earth converge,energy flow and logistics,and its characteristics affect the river terminal and offshore waters.In addition,mangrove and estuarine habitats are considered to be important sites for antibiotic resistance genes(ARGs)generation and transmission.The diversity and spread of ARGs were significantly affected by Marine and inshore human activities in these two habitats.However,there are few studies on the distribution pattern,antibiotic resistance mechanisms and driving mechanisms of ARGs in mangrove and estuarine habitats.Therefore,in order to comprehensively understand and clarify the distribution and transmission mechanism of ARGs in mangrove and estuarine habitats,this paper compared the metagenomic data of mangrove(Beihai,Fangchenggang,Hong Kong)and estuarine(Pearl River Estuary)habitats in China with the metagenomic data from public databases.To study the distribution characteristics and transmission mechanism of ARGs in mangrove habitats(China,India,Malaysia)and estuarine habitats(China,USA).This study was carried out in two aspects: after studying the distribution patterns of ARGs and antibiotic resistance mechanisms in mangrove and estuarine habitats,we further clarified the driving mechanisms of ARGs in the two habitats.The main results are as follows:1)Firstly,the distribution patterns of ARGs in six mangrove and estuaries were described.The main types of ARGs in both mangrove and estuarine habitats were multidrug,tetracycline and MLS.This also indicates that these three types of ARGs should be focused on and controlled in coastal wetland systems(mangroves,estuaries,etc.).The proportion of core subtype ARGs genes in different mangrove and estuarine habitats was 17.2% and 7.42%,respectively.According to the analysis of Alpha and Beta diversity and specific differences,although there were significant geographical differences in the distribution of ARGs in mangrove and estuarine habitats,the distribution of ARGs in estuarine areas was significantly different(P < 0.01).In summary,stable ARGs subtype genes may exist in mangrove habitats selected by the ecological environment of mangrove,while estuarine habitats are more dependent on local geography,climate,human influence and other factors,thus showing greater geographical differences.2)Secondly,the antibiotic resistance mechanisms of ARGs in mangrove and estuary areas were statistically analyzed to identify the key antibiotic resistance mechanisms.Metastats analysis of multi-group differences was further used to test whether there were significant differences in antibiotic resistance mechanisms in different regions.The results showed that ATP-dependant proteas was the main mechanism of antibiotic resistance in both mangrove and estuarine habitats.Target protection and Increased efflux were the second most common antibiotic resistance mechanisms in mangrove habitats,but it can be Enzymatic degradation in estuarine habitats.3)The effects of microbial communities and mobile genetic elements(MGEs)on ARGs transmission in mangrove and estuarine habitats were also analyzed.The results showed that Proteobacteria,Actinobacteria and Firmicutes were the main ARGs carriers in mangrove area,while Proteobacteria and Firmicutes were the main ARGs carriers in estuary area.Mobile genetic elements in the two habitats(mobile based elements,MGEs)are mainly for phage and replication/recombination/repair.Microbial and MGEs composition was the main route of ARGs transmission,with a comprehensive explanation of 89% and 82% in mangrove and estuarine areas,respectively.However,the effects of microorganisms and MGEs on ARGs were slightly different between mangrove and estuarine habitats.In mangrove habitats,the effect of microbial composition on ARGs was higher than that of MGEs,while in estuarine habitats,it was opposite.4)Finally,the relationship between ARGs and nitrogen and sulfur cycling genes in mangrove habitats was explored.Firstly,the composition and spatial heterogeneity of genes involved in nitrogen and sulfur cycling in different mangrove areas were described.Then,the correlation between nitrogen and sulfur cycling and ARGs was discussed by co-intertia Anaysis(Co IA)analysis and network modular analysis,and the key processes of nitrogen and sulfur cycling were identified.The results showed that the most closely related processes of ARGs were nitrification,nitrogen fixation and dissimilation nitrification and reduction.The most closely related processes of ARGs and sulfur cycle are mainly dissimilation and assimilative sulfate reduction processes.More importantly,in addition to statistical analysis,binning technology was also used to obtain factual evidence that nitrogen and sulfur cycling genes were associated with ARGs on the single bacterial genome.Overall,this study clarified the distribution pattern,antibiotic resistance mechanism and main transmission route of ARGs in coastal wetland systems.These information can provide a solid theoretical basis for the precise prevention and control of drug resistance in coastal wetlands in the future.For controlling the spread of antibiotic resistance,it is an important and effective means to prevent and control ARGs from the transmission route.Therefore,the results of this study will play a positive role in the prevention and control of ARGs in coastal wetland system.