Spatial Variation Of Antibiotic Resistance Genes And Adaptation Mechanism Of Bacterial Community Diversity In Hetao Irrigation District

Antibiotic Resistance Genes(ARGs)has been indentified as emerging environmental concern worldwide.Previous studies verified that ARGs could be horizontally transferred via mobile gene elements(MGEs)between bacterial communities on the process of horizontal gene transfer(HGT).ARGs could be transferred via food chain by consumption of vegetables that contain resistant bacteria,and threat the public health.The health of the agriculture ecosystem is not only closely related to the ecosystem safety but also to human health.Thus,it is necessary to determine the abundance and diversity of ARGs in agriculture ecosystem,especially in Hetao Irrigation District(HID),which is one of the most important irrigation districts in China.By using the theories and research methods of molecular ecology and community ecology,we study the abundance and diversity of ARGs in farmland ecosystems in HID of Inner Monginlia.The purpose is to reveal the relationship between environmental factors,ARGs and bacterial communities in soil,water and sediment environmental media,and to reveal the adaptive mechanism of bacterial community structure diversity and cooccurrence patterns of ARGs and bacterial communities.The main conclusions are as follows:1.The abundance and diversity of ARGs were significantly different among environment media.The subtype ARGs of mex F,sul I and sul II were the predominant resistance genes in the soil environment,respectively,the subtype ARGs of bla TEM was the predominant resistance genes in the water environment,and the subtype ARGs of aad A1,tet A,tet C and tet S were the predominant resistance genes in the sediment environment.The distribution of ARGs was significantly higher in the middle of study area both in soil and water environment,which means the agriculture activities and urban area might enhance the abundance of ARGs in HID.While,the abundance of ARGs in sediment,which was represent the accumulation level of ARGs abundance,was higher at the end of study area.The result indicated that the distribution of ARGs in sediment was influenced by the source of ARGs and the water propagation conditions.2.Results of correlation analyses indicated that significant positive correlations were found among soil organic matter SOM,available phosphorus AP and total nitrogen TN,as well as C and N content of sediment,with the predominant ARGs,which means the environmental factors may drive the occurrence of ARGs on a regional scale.The mobile gene elements of int I1,tnp A were detected in HID,and showed significantly correlated with most types of ARGs,especially correlated with the sulfonamide resistance gene,tetracycline resistance gene.These results indicated that the horizontal gene transfer process was possibly happened in the environment of HID,and MGEs promoted the transfer of ARGs among bacterial communities.3.The species richness level of bacterial community in HID is most abundant in sediments,followed by soil environment and lowest in water environment.Bacterial community composition is driven by the co-stress of environmental factors and ARGs.When the environment properties narrow down the ecological niches for indigenous microorganism,the ARGs could enhance the abundance of resistant bacterial communities.Network analysis revealed co-occurrence patterns between ARGs and potential bacterial hosts.Results showed that the dominant bacterial community Proteobacteria and Firmicutes had been recognized as the potential bacterial hosts,which carrying ARGs of aad A1,aad A2,aph A3,sul I,sul II,tet B,tet R,tet E and MGEs of int I1,tnp A genes in the agriculture ecosystem of HID.These results of network analysis,under different bacterial classification levels,revealed that the bacterial on phylum or genus level also showed co-occurrence relationships with ARGs in different environments.In summary,this work analyzed the current status of ARGs in agriculture farmland ecosystems of HID,and clarified the key environmental factors which most correlated with the occurrence and abundance of ARGs,and also examined the abundance and diversity of bacterial communities.The bacterial community were significantly different among environment media on the spatial scale.Environmental factors and ARGs played an important role in changing bacterial community structure.Both of them drove the adaptive evolution mechanism of the dominant bacterial community and the resistant bacterial community.These findings provided a better understanding on occurrence and distribution of ARGs,and revealed their relationship with microbial community succession.These results also provided a scientific basis for preventing and controlling the spread of ARGs,and were great significance for protecting ecosystem security.