| Objective: Antibiotic resistance genes(ARGs)pollution caused by decomposition of animal carcasses has become an environmental issue that requires attention,which is crucial for maintaining the aquatic environment and human health.However,carcasses can bring amounts of toxic chemical substances,and the relationship between these products decomposed by animal cadavers and ARGs is unclear.To tackle this problem,this study selected the main products(i.e.,putrescine and cadaverine)as research objects,and designed indoor laboratory experiments with putrescine and cadaverine exposure.Thus,this study was to explore the changes and influencing factors of ARGs,and the relationship between high-risk ARGs and pathogenic related bacteria under exposure of putrescine and cadaverine.Methods: Based on the indoor laboratory experiments,this study set up four parallel groups: control group(in a natural environment),putrescine alone exposure group,cadaverine alone exposure group and both mixed exposure group.Meanwhile,we applied high-throughput quantitative PCR technology,high-throughput sequencing,water samples and sediment physicochemical analysis methods to explore the responses of ARGs,mobile genetic elements(MGEs),microbial community and physicochemical factors in the water and sediment to high-dose putrescine and cadaverine exposure and the influencing factors of ARGs,especially to focus on the relationship between highrisk ARGs and pathogenic related bacteria.Results:(1)Putrescine and cadaverine exposure changed most physicochemical factors in the water and sediment of the Yellow River.Putrescine and cadaverine significantly increased the conductivity,salinity,p H,total carbon and total nitrogen,while significantly decreasing oxidation reduction potential in water and sediment.(2)For the ARG type and resistance mechanism,the highest proportions were the tetracycline resistance genes and antibiotic deactivate,respectively.Under the exposure of putrescine and cadaverine,the total relative abundance of ARGs and MGEs in water was higher than that in sediment.(3)Under the exposure of putrescine and cadaverine,six ARG types(i.e.,β-Lactamase,chloramphenicol,sulfonamide,tetracycline,vancomycin and other resistance genes)were significantly positively correlated with transposase(Tp614).(4)In addition,the microbial community in water and sediment was significantly changed by putrescine and cadaverine,which putrescine and cadaverine decreased the alpha diversity in water.(5)Six high-risk ARGs and fifteen pathogenic related bacteria were identified,and both were mainly enriched in sediment exposed to putrescine.This study confirmed positive correlations between the abundance of high-risk ARGs like erm B and the abundance of pathogenic related bacteria like Burkholderia.Conclusions:(1)Putrescine and cadaverine changed most environmental factors.The exposure of putrescine and cadaverine increased the total nitrogen and carbon in the Yellow River water and sediment,indicating that putrescine and cadaverine exposure may cause eutrophication of the aquatic environment.(2)Putrescine increased ARG diversity in sediment,the ARG number and resistance mechanism.Compared with the putrescine group,both putrescine and cadaverine exposure increased the relative abundance of sulfonamide and tetracycline resistance genes in sediment,indicating that putrescine and cadaverine may promote the prevalence of ARGs.(3)Under the exposure of putrescine and cadaverine,most ARGs in the Yellow River water and sediment were positively correlated with the abundance of transposase(Tp614),suggesting that exposure to putrescine and cadaverine would promote the transmission of resistance level genes in the environment.(4)Putrescine and cadaverine exposure changed the microbial community in water and sediment.Compared with the control group,the community differences in exposure treatments gradually increased according to the order of cadaverine exposure,putrescine exposure and both exposures.This indicated that putrescine and cadaverine can cause differentiation and succession of microbial communities.(5)Our study showed a strong positive correlation between high-risk ARGs and multiple pathogenic related bacteria under exposure to putrescine and cadaverine,indicating that exposure to putrescine and cadaverine may promote pathogenic related bacteria in water and sediment to carry high-risk ARGs,thereby leading to the prevalence of antibiotic resistant bacteria in human living environments.Thus,the relationship between ARGs and influencing factors,especially between high-risk ARGs and pathogenic related bacteria under cadaverine and putrescine would help understand the influences of putrescine and cadaverine on the aquatic environment and public health,providing references for environmental pollution management measures and protection of public health. |
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