| Antibiotic resistance genes(ARGs),as an emerging environmental pollutant,are widespread in rivers.In this study,water,sediment and plastic in the Lhasa River from Mozhugongka county to Qushui county were selected as research abject to investigate the distribution ofARGs and its factors via real-time quantitative PCR and 16S r DNA sequencing technology.The spatial distribution characteristic and the main influencing factors ofARGs were revealed in the river by analyzing the relationship the relationship amongARGs,environmental factors(heavy metals)and microbials in water,sediment and plastic.There were main conclusions followed:The contents of heavy metals in sediments and plastics were higher.The mean contents of Pb andAs in sediments reached 125.91 mg/kg and573.71 mg/kg,respectively.The average contents of Cu and Zn on plastic were 107.32 and 171.17 mg/kg,respectively.However,the concentrations of heavy metals in the water were less than 10?g/L.A significant correlation was found between Cu,Cd on plastics and those in water,probably suggesting the adsorption and distribution equilibrium mechanism of heavy metals between plastics and water.There were significant differences inARGs among different regions.The abundance of antibiotic resistance genes in water decreased significantly from upstream to downstream,while it was just the opposite on plastic.The abundance ofARGs in sediments was the highest in Lhasa city(1.08×10-2-1.72×100 copies/16S r DNA),followed by Qushui county(2.04×10-2-2.88×10-2 copies/16S r DNA),and the lowest in Mozhugongka county(4.60×10-3-2.20×10-2copies/16S r DNA).?-lactam resistance gene bla TEM(ND-7.02×100 copies/16S r DNA)and tetracycline resistance gene tet M(ND-2.73×100copies/16S r DNA)were the mainARGs in Lhasa River,and their relative abundance was more than 90%of?ARGs,especially water sample at site 2,where relative abundance of bla TEMreached 7.02 copies/16S r DNA.The effects of heavy metals onARGs were different among the three media:aadA,str B in water were affected by Cr,Cu(P<0.05),only bla CMY on plastic was affected by heavy metals(Cr,Cu;P<0.05),while theARGs in sediments were not affected by heavy metals.Those might be related to the occurrence state of heavy metals.Compared to integron intI1,the detection rate of transposon tnpA was higher in the river,which was 90%in sediments and plastics,and 100%in water.while the detection rate of int I1 was only 30%on plastics and 70%in water and sediment.Int I1 and tnpA were significantly positively correlated with variousARGs(e.g.,sul1,sul2),probably contributing to the enrichment ofARGs in rivers.Proteobacteria and Bacteroidetes were the predominant phyla in the microbial communities of water,sediment and plastic.The indexes of richness(Chao1 index:3192.3)and diversity(Shannon Weiner index:6.30)of OTUs in sediment were significantly higher than those of water and plastics(P<0.05).Significantly differences were found in the composition and structure of microbial communities among water,sediment and plastic(P<0.05).In the plastic community,the abundance of Proteobacteria was higher(61.54%)than it of water and sediment,Acidobacteria(6.66%)was enriched in the sediments,and Firmicutes(5.98%)was higher in the water than it of plastic and sediment.The more significant differences in composition of microbial were found at more accurate taxonomic levels by Linear DiscriminantAnalysis(LDA).The results of the co-occurrence analysis between microorganism andARGs were showed that 51,80 and 74 potential hosts ofARGs were in plastics,sediments and water,respectively.Thereinto,10 genera were detected in the three media,such asAcetoanaerobium,Acidovorax,Bacteroides,Cloacibacterium,Enterococcus and Simplicispira.These potentially resistant bacteria exposure to the environment might increase the risk of drug resistance in the river ecosystems.In summary,this study analyzed antibiotic resistance gene contamination in multiple media in the downstream of Lhasa River,and clarified the main factors aggravating antibiotic resistance gene contamination in the study area,as well as the microbial composition and diversity.Heavy metal pollution and mobile genetic elements are the important factors for the accumulation of antibiotic resistance genes in the environment,which together lead to the prevalence of antibiotic resistance genes in bacterial communities and the differences in theARGs host among different media.This study are helpful to understand the pollution status of antibiotic resistance genes in the downstream of Lhasa River,and provide a basis for the prevention and control of antibiotic resistance gene pollution in Lhasa River,which is of significance for ecological and environmental protection... |
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