Study On The Aftereffect Of Antibiotic Removal And The Mechanism Of Resistance Gene Transfer In Bioelectrochemistry-enhanced Constructed Wetland

After the pressure of antibiotics is relieved,the strengthening effect of the bioelectrochemical system may lead to the constructed wetland becoming a reservoir of resistance genes,which seriously threatens the aquatic ecological security.Therefore,we constructed a microbial electrochemical constructed wetland(MES-CW)and explored the multi-media occurrence characteristics of antibiotic resistance genes(ARGs)under different antibiotic selective pressures.The key driving factors of resistance gene transfer in MES-CW were identified,and the mechanism of resistance gene transfer in the system after antibiotic pressure relief was revealed,which provided an important support for the safer purification of antibiotic-containing wastewater by bioelectrochemical enhanced constructed wetland.The main conclusions are as follows :Firstly,we found that the removal efficiency of nitrogen,phosphorus and SMX by MES-CW was higher than that by CW.Compared with CW,the removal rates of ammonia nitrogen,nitrate nitrogen,phosphate and SMX by MES-CW at different concentrations of SMX increased by 0-26.98 %,22.23-53.24 %,2.24-28.89 % and8.34-11.30 %,respectively.After the release of SMX pressure,the electrochemical technology increased the total abundance of ARGs in the constructed wetland system,and the negative aftereffect appeared.With the decrease of SMX concentration,the total abundance of ARGs in MES-CW water samples was always higher than that in the substrate.In water samples,multidrug resistance genes and sulfonamide resistance groups were the main types of ARGs in constructed wetlands with the decrease of SMX concentration.After SMX pressure relief,the total abundance of ARGs in MES-CW increased by 36.1 %compared with 0.1 mg / L;the relative abundance of multi-drug resistance genes and their subtypes increased by 69.2-292.5 %,and the relative abundance of sulfonamide ARGs and their subtypes increased by 83.5-116.3 %.Electrochemistry aggravated the negative post-effect of ARGs in water samples(the total abundance of ARGs increased by 95.42 % compared with CW,and the relative abundance of sulfonamide ARGs and sul1 increased by 126.3-148.7 %).In the substrate,the total abundance of ARGs in the MES-CW substrate decreased with the decrease of SMX concentration.When the pressure of SMX was relieved,the total abundance of ARGs in MES-CW increased by33.62 % compared with 0.1 mg / L.The relative abundance of sulfonamides increased by 41.6 %,and the relative abundance of sul1,sul2 and sul4 increased by 100-126 %.The relative abundance of multidrug resistance genes and their subtypes increased by106.7-195.2 %.The matrix also showed negative aftereffect,but the degree was less than that of water samples.Under different SMX pressures,the key factors driving the occurrence characteristics of resistance genes in constructed wetland systems changed significantly.Under high concentration of SMX,the selective pressure of SMX and the abundance of Firmicutes are the key driving factors affecting the transfer of ARGs.At low concentrations of SMX,nitrate concentration and the abundance of Proteobacteria were the key driving factors affecting the transfer of ARGs.By using voltage regulation(voltage increased from 0.6V to 10V)to reduce the negative aftereffect after SMX pressure relief,it was found that the total abundance of ARGs in water samples was reduced by 80.7 %,and the high voltage significantly reduced the relative abundance of multi-drug resistant and sulfonamide ARGs.When the pressure of SMX was relieved,electrochemical technology mainly increased the total abundance of ARGs by promoting the proliferation of drug-resistant bacteria.From the perspective of the key host bacteria of ARGs,when the SMX pressure was relieved,the host of ARGs in the water sample(ornithine klebsiella)increased by 300 % compared with 0.1 mg / L;the matrix was mainly due to the increase in host species,which increased by 4 and 3 hosts compared to 10 and 0.1 mg/ L.Moreover,we found that the relative abundance of integrase and recombinase in water samples and integrase in matrix increased by 2-9 % after SMX pressure relief,but the binding ratio of ARGs to mobile genetic elements(MGEs)decreased significantly after SMX pressure relief,indicating that the increase of drug-resistant bacteria after SMX pressure relief is the main reason for the negative effect.In addition,the content of ROS in the matrix biofilm is synchronized with the changes of ARGs.Low concentration of ROS can play a role in signal transduction and stimulate metabolism,thereby increasing the activity and richness of microorganisms.