Study On Propagation Mechanism Of Antibiotic Resistance Gene In Landfill Reactor And Effect Of Leachate Recirculation

Urban landfills have become a repository of antibiotic resistance genes?ARGs?,with potential deficiencies in the surrounding environment as effluent from landfills such as leachate.However,the impact of exposure to antibiotics and heavy metals in landfills on ARGs in different landfill environments is still unclear.In this study,a landfill reactor was constructed in the laboratory to study the effect,that the abundance of ARGs in landfills under the exposure of antibiotics?sulfadimethylpyrimidine?SMZ?,penicillin?PenG??and heavy metals?potassium chromate,zinc sulfate?in facultative and anaerobic environments,molecular techniques and correlation analysis were used to analyze the potential hosts carrying ARGs and the key factors driving ARGs changes,and to clarify the propagation mechanism of ARGs in landfill systems.At the same time,the leachate recirculation landfill reactor was studied to investigate the effect of recharge on ARGs.The main findings of this paper are as followed:?1?Study on the variation characteristics of ARGs during landfill:The reactor was constructed,and the changes of ARGs of leachate and solid waste were investigated under the conditions of exposure to selected substances?antibiotics,heavy metals?in different operating conditions?facultative,anaerobic?.The abundance of ARGs in leachate was in the range of 3.0–10 log₁₀?copies/mL?.The abundance of ARGs was TCs,BLs,MLs,ACs and SAs ARGs.The dominant genes were tetM,ermB,bla_TEM,aadA1,sul1;the addition of antibiotics led to an increase in bla_TEM abundance in the anaerobic environment.Under anaerobic conditions,the addition of antibiotics led to an increase in the abundance of other dominant genes except bla_TEM.And ARGs likely to participate in HGT which were significantly positively correlated with the movable gene components intl1 and intl2?P<0.05?were strB,mefA,and tetM.The abundance of ARGs in solid waste was BLs,TCs,MLs,ACs and SAs,and the dominant genes were bla_OXA,tetM,ermB,aadA1,sul1 in both facultative and anaerobic environments.The addition of antibiotics resulted in an increase in the abundance of sul1 and intl1,while the addition of heavy metals resulted in a decrease in the abundance of intl1.In the anaerobic environment,the abundance of tetM was significantly reduced?P<0.05?,and the addition of heavy metals accelerated this process.The target genes significantly associated with the mobile gene elements intl1,intl2 were ermB,sul2,mefA,tetQ,tetM,mexF.?2?Study on the propagation mechanism of ARGs in landfill reactorsThe study found that the concentration of TN and TP in the leachate decreased significantly from 3543.68±288.26 mg/L and 7.17±2.60 mg/L?P<0.05?to614.83±33.46 mg/L and 0.41±0.35 mgwith the operation of the reactor,respectively,and TN,TP,NO₃^--N and other ARGs were significantly correlated under facultative and anaerobic conditions?P<0.05?;the concentrations of TN and TP in solid waste were significantly decreased from 6.27±1.29 mg/kg and 4.35±0.36 mg/kg to 3.75±0.41mg/kg and 3.67±0.41 mg/kg?P<0.05?,respectively,and there was a significant correlation between TN and TP and int1 and aadA1 in facultative environment?P<0.05?.The bacterial community structure changed during the landfill,but the dominant flora remained basically unchanged.In the leachate samples,the dominant bacteria were Proteobacteria,Parcubacteria,Saccharibacteria,Bacteroidetes,Firmicutes and WS6,and the relative abundance ranged from 7.24±7.72%to 20.88±10.51%.The presence of antibiotics resulted in a significant decrease in the relative abundance of Proteobacteria in the facultative environment?P<0.05?,and the presence of heavy metals resulted in a significant increase in the relative abundance of actinomycetes?P<0.05?,and the bacteria which positively associated with ARGs mainly were Synergistetes,Candidatus,WS6,WWE3 and Teneriquets?P<0.05?;heavy metals in anaerobic environment resulted in a significant decrease in the relative abundance of Proteobacteria?P<0.05?,and the bacteria that were significantly positively correlated with ARGs were Bacteroidetes,Saccharibacteria and Firmicute?P<0.05?.?3?Influence of leachate recirculation on the change of ARGs in landfill reactorsThe total abundance of target ARGs in leachate varied from 10.25 to 11.37 log₁₀?copies/mL?,and the addition of heavy metals led to the increase of the sul1 abundance,and the addition of antibiotics led to the decrease of the intl2 abundance under facultative conditions?P<0.05?.And the addition of antibiotics also resulted in the decrease of the abundance of intl2 in the anaerobic environment?P<0.05?.During the reperfusion process,the mobile gene components intl1,intl2 and TN still showed a correlation with the dominant genes in the leachate?P<0.05?,while the increase in the content of MGEs and nitrogen compounds in the effluent resulted in no significant removal of ARGs,even enrich.In solid waste,the total abundance of ARGs was in the range of 11.0–12.5 log₁₀?copies/g?,and its structural composition was consistent with that of the dominant gene in leachate.After reperfusion,only mexF was effectively removed from solid waste?P<0.05?,and other genes were enriched by 1-2 orders of magnitude.In addition,the correlation between MGEs and ARGs in the solid phase was lower than that of leachate,but the effect of nitrogen compounds on ARGs still existed?P<0.05?.In summary,this study explored the changes and mechanism of ARGs in landfill reactors exposed to antibiotics and heavy metals under different operating conditions,revealing the effects of physical and chemical indicators and microbial communities on the spread of ARGs,pointing out the limitation of leachate recharge to control the pollution of ARGs in landfills.And it has the theoretical significance for the management and control of ARGs in landfills.