Molecular Ecological Mechanism Of Ultraviolet Disinfection Effects On Microbial Antibiotic Resistance In Sewage

The intensive use and abuse of antibiotics may accelerate the dissemination of antibiotics resistance genes(ARGs)and increase the diversities and abundances of ARGs and antibiotics-resistant bacteria(ARB)in the natural environments,which is posing enormous challenges and threats on the environmental safety and human health.Wastewater treatment plants(WWTPs)are the main environmental reservoirs of ARGs,and many kinds of ARGs have been detected in WWTPs.Ultraviolet(UV)disinfection is an effective disinfection method widely used to inactivate the bacteria in water.Previous studies have mainly been focused on the removal of some specific ARB and ARGs by UV disinfection;however,the detailed mechanisms of UV disinfection effects on microbial antibiotic resistance in sewage still remain unknown.In this study,UV disinfection was applied in the lab scale reactor to explore 1)the changes of microbial antibiotic resistance,2)the diversities and abundances of ARGs and MGEs,and 3)the relationship between the distribution of ARGs and the changes of MGEs and microbial community structure.Based on these,the molecular mechanisms of UV disinfection effects on microbial antibiotic resistance were investigated.Overall,this study provided the theoretical and technical knowledge for the optimization of UV disinfection technology.The main research contents and results are as follows.1)The changing profiles of microbial antibiotic resistomes by UV disinfectionThe results showed that 50 mJ/cm2 UV radiation could not effectively inactivate the bacteria in the wastewater samples,while 500 mJ/cm2 and 2000 mJ/cm2 UV radiation could significantly damage the bacteria.The bacterial viability tended to recover after the photoreactivation.Overall,the total relative abundance of ARGs increased after UV radiation.The relative abundance of multidrug resistance genes increased by 24.34%?54.05%after UV treatment.The abundance of the ARGs responsible for effmux pump also increased greatly(25.47%?46.28%)after UV disinfection.High-throughput sequencing and bioinformatics analysis showed that a total of 159 ARGs in all the samples belonging to 14 types.Among the detectable 159 ARGs,42 persistent ones belonging to eight types were commonly shared by all the samples and their abundance accounted for 70.0%?89.4%of total ARGs abundance in the samples.Among the persistent ARGs,bacA gene and multidrug resistance genes within RND transportation system had apparently higher abundance after UV disinfection.2)The molecular ecological mechanism of bacterial community structure effeects on microbial antibiotic resistanceThe results suggested that UV disinfection could greatly affect bacterial community structure.At the genus level,the percentage of Pseudomonas increased greatly after UV disinfection,and increased by the highest value 20.89%when the UV dose was 500 mJ/cm2.Within the genus Pseudomoas,Pseudomonas aeruginosa seemed to play an important role in the alteration of microbial diversities.UV radiation may lead to the mutations of the RND efflux pump related genes,which could cause the overexpression of RND efflux pump,and then promote the antibiotic resistance of Pseudomonas aeruginosa.Pseudomonas,Bacteroides,Trichococcus and Bacillus were significantly correlated with the distribution of the persistent ARGs(p<0.05,R2>0.5).The distribution of bacitracin resistance genes was positively correlated with the abundance of Bacillus(p<0.05,R2>0.5).The distribution of most of multidrug resistance genes encoding RND transportation system was affected by Pseudomonas in a positive manner(p<0.05,R2>0.5).3)The molecular ecological mechanism of MGEs effects on microbial antibiotic resistanceOverall,the relative abundance of integrons,plasmids and insertion sequences(ISs)increased after UV treatment.UV disinfection could greatly affect the diversities of MGEs.Intll had the highest abundance and occupied 86.9%?99.1%among all the integrase genes.Among the ISs,the relative abundance of ISAav2,ISAav3,ISPst3,lSPst2,ISPsy20 and ISUnCu4 increased while ISPpsl,ISAs1,ISAs2 and ISKpn3 decreased after UV disinfection.The relative abundance of most of the plasmids increased after UV disinfection,especially for pSWIT02,pSWIT01,pCAR3,pA81,megaplasmid and pGMI1000MP.Linear regression analysis showed that the relative abundance of ARGs was positively correlated to the levels of MGEs(R2=0.877),especially for ISs(R2=0.954)and plasmids(R2=0.852).Besides,the Pearson correlation analyses showed that intIl,intl3 and intIQ were positively correlated with bacA gene and RND efflux pump related genes(p<0.05,R2>0.5).ISKpn1,ISPpu14 and ISPf12 were positively correlated with RND efflux pump related genes(p<0.05,R2>0.5).Megaplasmid,pA81,peAR and pGMH1000MP were positively correlated with bacA gene and RND efflux pump related genes(p<0.05,RZ>0.5).VPA showed that MGEs and bacterial communities were important to the ARG changes during the UV disinfection process and explained 36.19%and 37.61%of the variation of ARGs,respectively.