Distribution Characteristics And Traceability Analysis Of Antibiotic Resistance Genes In Nandu River,Hainan Island

Antibiotic resistance genes（ARGs）,as a new type of pollutant,are widely and extensively present in the natural environment.The Nandu River is the largest river in Hainan Island and a typical large-scale tropical river in China.It is a precious freshwater resource that people rely on for survival.Analyzing its distribution characteristics and transmission pathways of ARGs in the river has profound significance.This study collected surface water,sediment,and habitat samples from the upper,middle,and lower reaches of the Nandu River in January and July 2022,respectively.Metagenomic technology was used to analyze the distribution of ARGs and microbial communities,in order to explore the changing characteristics of ARGs in different spatial patterns of the river.By combining Spearman correlation and ordination analysis,we further explored the correlation between the distribution of ARGs,physicochemical factors and heavy metals.The variance partition analysis（VPA）was used to analyze the joint mechanism of environmental factors on ARGs.At the same time,a partial least squares path model（PLSPM）was used to attempt to clarify the interaction between ARGS,microbial communities,and environmental factors,in order to achieve traceability analysis of ARGs transmission pathways in three environments.The main results are as follows:1.A total of 21 types of ARGs were detected in water,and multidrugs was the most frequently detected and relatively abundant ARGs,with a detection rate of 100%at all points.These ARGs against Macrolide-Lincosamide-Streptogra（MLS）,tetracycline,glycopeptide,peptide,and sulfonamide also had higher relative abundances,and they were dominant.There were significant differences in the spatial composition of winter ARGs,and significant differences in the diversity of summer ARGs.221 phyla of microbial communities were detected in water,and the dominant phyla was mainly composed of Proteobacteria,Actinobacteria,Cyanobacteria,Bacteroidetes,and Acidobacteria.There were significant differences in the spatial composition of microbial communities.In winter,ORP,p H,NO₃^--N,NH₄⁺-N,TP,Ni,Zn,Co,Fe,and Be were the main factors affecting ARGs,but in summer TN,p H,DO,COD_cr,Co,Mn,Cu,As,and Be were the main factors.VPA found that winter environmental variables could explain 97.0%of changes in ARGs,while summer environmental variables could explain 81.0%.2.A total of 21 types of ARGs were detected in sediment,and the top ten dominant categories were consistent with water.Only sulfonamide ARGs were not detected as dominant ARGs in sediment,while multidrug ARGs were still the ARGs with the highest detection frequency and relative abundance.The relative abundance of dominant categories was slightly different.There was no significant differences in the spatial composition and diversity of ARGs between the two seasons.In sediment,225 microbial phyla were detected in winter and 223 in summer,with dominant phyla similar to water.Only Nitrospirae and Euryarchaeota were different from water,and were dominant phyla in sediment.Microbial communities showed significant differences in spatial composition.In winter,TK,p H,TN,NO₃^--N,AP,AK,Li,As,Pb,Co,and Zn were the main factors affecting ARGs.In summer,TN,NO₃^--N,NH₄⁺-N,AP,AK,Li,As,Zn,and Mn were the main factors.Winter environmental variables could explain 82.0%of changes in ARGs,while summer environmental variables could explain 77.0%.Among them,microbial communities had the highest individual explanatory power for ARGs.3.A total of 21 types of ARGs were detected in the soil from the hydro-fluctuation belt,and the dominant category of ARGs detected was consistent with that of the water.Multidrug ARGs remained the most dominant category.There was no significant difference in the spatial composition and diversity of ARGs between the two seasons.In winter,224microbial phyla were detected in the samples of the hydro-fluctuation belt,while in summer225 were detected.The dominant phylum was similar to the water,except for the Nitrospirae and Thaumarchaeota,which were different from the water.They were the dominant phylum in the hydro-fluctuation belt,and there were significant differences in the spatial composition of microbial communities.In winter,p H,SOM,TP,AP,NH₄⁺-N,AK,Cu,Pb,Co,Zn,and Ag were the main factors affecting ARGs.In summer,p H,SOM,AP,NO₃^--N,AK,TK,Li,Cd,Cr,Zn,Pb,Mn,and Ag were the main factors affecting ARGs.Winter environmental variables could explain 56.0%of changes in ARGs,and summer environmental variables could explain a 65.0%.4.The PLSPM showed that there were significant seasonal differences between environmental factors,microbial communities,and ARGs.In winter,the microbial communities in the hydro-fluctuation belt showed a significant positive effect on ARGs and a signifit negative effect on water ARGs.The water environmental factors had a significant negative effect on ARGs and sediment environmental factors.It could be seen that the hydro-fluctuation belt affectd the water ARGs,thereby affecting sediment ARGs.The transmission pathways of ARGs in the three habitat samples showed a trend from hydro-fluctuation belt to water to sediment.In summer,water environmental factors had a significant positive effect on ARGs and sediment environmental factors;The environmental factors in the subsidence zone had a significant positive effect on ARGs by affecting microbial communities.It could be seen that the water environment could affect sediment ARGs,while the environmental factors in the subsidence zone had a self responding relationship with ARGs and had no significant correlation with other environments.