| Antibiotic-resistant bacteria（ARB）and antibiotic resistance genes（ARGs）are now emerging environmental contaminants that are simple to propagate and remain in the environment,posing a serious hazard to human health and development.The environmental effects caused by the ARGs carried by ARB can also be increased by horizontal gene transfer（HGT）,which occurs when genes are transferred across microbes.Conjugation,transformation,and transduction are all parts of HGT.The primary way of ARGs transfer in these pathways is thought to be conjugation,which commonly takes place across closely related strains（within genera）or bacterial species.The removal of ARGs can be achieved by conventional methods,such as membrane bioreactors,constructed wetland systems,membrane filtration,chlorine disinfection,and UV disinfection.However,during actual treatment,biofilm is prone to deterioration and separation;the operation of constructed wetland system is not necessarily stable;membrane contamination will affect the removal of ARGs during membrane filtration,and the accumulation of ARB and ARGs on membranes may promote the horizontal transfer of genes;during chlorine disinfection,the removal of ARGs depends on the available chlorine concentration,and the production of chlorinated disinfection by-products will also promote the horizontal transfer of genes.Much effort has been paid to the application of advanced oxidation processes（AOPs）to eliminate ARB and ARGs from water.Strong oxidized free radicals alter the permeability of cell membranes,impair enzyme activity,and damage cell DNA.Based on the above situation,discharge plasma technology was used to study the removal of ARGs from wastewater and the inhibition effect on pathogenic transmission,as well as the influence and mechanism on the horizontal transfer of ARGs.The following are the key findings of the study:（1）The removal effect and mechanism of ARGs from effluent by discharge plasma were studied.After 25 min of discharge plasma treatment,aac（3）-II,bla TEM-1,TetW and TetC removed about 1.32 log,1.34 log,2.39 log and 2.80 log,respectively,and the removal of ARGs was due to the attack of·OH,1O2and so on.Dissolved organic matter with fluorescence was decomposed during the treatment.The richness and diversity of microbial communities carrying ARGs and mobile genetic elements decreased after the treatment.The content of Int I1 decreased by about 2.46 log after 25 min of discharge treatment,which was significantly positively correlated with the removal of ARGs.The expression levels of genes related to ATP binding,DNA repair,gene transfer and cell membrane were decreased after plasma treatment,indicating that the expression pathways of multiple genes were inhibited from multiple aspects by discharge treatment,thereby achieving effective ARGs removal.In addition,discharge treatment also suppresses the expression of pathogenic genes associated with lumpy skin disease,Niemann-Pick disease,polycystic kidney disease,and liver disease,reducing the risk of transmission of pathogenic species.（2）The effect of discharge plasma on horizontal transfer of ARGs and its mechanism were studied.After 5 min of discharge plasma treatment,the inactivation rate of AR E.coli reached3.35 log CFU m L-1,and the inactivation rates of histidine,mannitol and p-benzoquinone were 1.62,1.76 and 2.03 log CFU mL-1,respectively.The results showed that the removal of AR E.coli by the discharge system was significantly inhibited.After plasma treatment,the morphology of AR E.coli was significantly changed,the intracellular ATP and ROS levels were significantly decreased,and the MDA and enzyme activities（SOD,CAT）showed an upward trend,indicating that the cells were damaged to different degrees.The transfer frequency of untreated AR E.coli was 2.90×10-5in conjugation transfer and 3.05×10-6after discharge treatment,indicating that discharge treatment could inhibit the frequency of horizontal gene transfer.The transfer frequencies of histidine,mannitol and p-benzoquinone groups were 1.21×10-5,8.26×10-6and 6.17×10-6,respectively,which were slightly higher than that of the pure discharge group.When thiourea was added to the transfer system,the transfer frequency was significantly decreased,indicating that ROS plays a key role in the AR E.coli transfer system.At the same time,the expression of HGT-related genes such as ROS formation and SOS response,cell membrane permeability,outer membrane protein coding genes,and conjugation-related genes showed a downward trend compared with those at 0 min of treatment,which indicated that plasma treatment could effectively inhibit the horizontal gene transfer of AR E.coli and reduce the risk of its transmission in the environment.Discharge plasma can effectively remove ARGs from actual water,and the reactive species produced by discharge plasma are an important reason for ARGs removal.At the same time,discharge plasma can effectively inhibit the horizontal gene transfer of AR E.coli,so as to effectively control the risk of antibiotic resistance transmission. |
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