Characteristics Of Biofilms And Resistance Genes On Microplastic Surfaces In Waste Water Treatment Plant

Microplastics are emerging pollutants that attract attention due to their wide distribution and potential harms.Biofilms on microplastics can promote plastic deposition and animal feeding,which have attracted widespread attention from researchers at home and abroad.Although many reports have studied the characteristics of biofilms on microplastics in the ocean,there are few reports on the interaction between microplastics and microbial communities in freshwater.Waste water treatment plant is one of the important sources of microplastics entering the freshwater,and its technology cannot completely remove microplastics.However,the characteristics and potential hazards of microplastics carrying biofilms in waste water treatment plants remain unknown.In order to study the characteristics and environmental effects of biofilms attached to the surface of the microplastics entering the waste water treatment plant,the research put typical microplastics into a waste water treatment plant in Qingdao.Using LSCM,AFM,FTIR,16S rDNA sequencing,metagenome sequencing and other technical methods to study the spatial distribution,thickness,relative abundance and type of resistance genes of biofilms on microplastics,and the effect of biofilms on surface morphology of microplastics.The main conclusions of this study are as follows:(1)It was found that microplastics in the waste water treatment plant can become carriers for the attachment of microorganisms.AFM was used to measure the thickness of biofilms,and it was found that the biofilm thicknesses of different microplastics were different.PE in aerobic tank had the largest biofilm thickness.The amount of biofilms were related to hydrophobicity,surface roughness and culture environment.The greater the hydrophobicity and surface roughness of the microplastics,the more likely they were to be adhered by biofilms.And the amount of biofilms in aerobic tank were higher than that in anaerobic tank.Observation using AFM and FTIR found that biofilms had the potential to degrade microplastics,which can change the surface roughness of microplastics and expose microplastics to more functional groups.(2)It was found that microplastics were unique microbial carriers by 16S rDNA sequencing.The composition of the bacterial community on the biofilms was different from that of the sludge.The species composition of microplastic biofilms cultured in different environments also varied,mainly reflected in the species and abundance of dominant bacteria.Meanwhile,the species diversity index(Chao1 index and Shannon index)of biofilms were higher than that of sludge,and microplastics can enrich microorganisms in the environment.In addition,Enterobacteriaceae can be detected on microplastics,so microplastics may become carriers of pathogenic bacteria and assist in the spread of pathogenic bacteria.(3)Metagenomic sequencing revealed that resistance genes could be detected on microplastics,such as multidrug,beta-lactam,sulfonamide,bacitracin,aminoglycoside,macrolide-lincosamide-streptogramin and tetracycline.Therefore,microplastics can be used as carriers of resistance genes,and the resistance genes can be transmitted to rivers or oceans through the effluent of waste water treatment plant.The results of this study point out the uniqueness of microplastics as the microbial carrier and the potential hazards of pathogenic bacteria and resistance gene carriers,providing theoretical support for the safety assessment of microplastics in waste water treatment plant.