Effects And Mechanism Of Polystyrene Micro(nano) Plastics On Antibiotic Resistance Genes In Activated Sludge

Antibiotic resistance genes(ARGs)and Micro(nano)plastics(NPs/MPs)have been regarded as emerging environment contaminants and have attracted growing attention owing to their widespread presence in the environment.Among them,sewage treatment plant was considered as an important reservior of environment.However,the studies related to the impact of NPs/MPs onARGs have focused on the environment media such as ocean,river and soil.In addition,few researchers have explored the interaction between NPs/MPs andARGs in the sewage treatment plant.The effects of NPs/MPs size and concentration onARGs have been rarely investigated.Furthermore,ARGs in sewage treatment plants may exist in a variety of forms,including intracellularARGs(iARGs),extracellular fixedARGs(aeARGs)and freeARGs(feARGs),but the effect of NPs/MPs on different forms ofARGs is still unknown.The objective of this article is to evaluate the effects and mechanism of polystyrene(PS)with different concentrations(0.5 mg/L and 50 mg/L)and sizes(NPS/MPS)on different forms ofARGs and resistant bacteria(ARB)in activated sludge.To achieve this goal,samples were collected from secondary sedimentation tank in a sewage treatment plant,and conduct exposure experiment.The abundances of ARB andARGs were quantified by drug sensitivity test and quantitative real-time polymerase chain reaction(q PCR),respectively.The key factors affectingARGs and ARB by NPs/MPs were evaluated by reactive oxygen species(ROS),proportion of living cells,gene expression,horizontal transfer and bacterial community.The main conclusions are as follows:(1)PS facilitated the proliferation of ARB in activated sludge,the absolute concentration of sulfonamides and tetracyclic ARB increased to1.77 and 1.57 times of the initial level.The promoting effect of 50 mg/L PS on ARB was significantly stronger than that of 0.5 mg/L PS.Sulfonamides ARB increased more under the action of micron PS,while tetracyclines were more sensitive to nano PS.Under the exposure ofμm-PS,sulfonamides ARB increased dramatically,while tetracyclic ARB was increased upon nm-PS.(2)Upon exposure to the environmentally relevant(0.5 mg/L)and high concentration(50 mg/L)of PS,the absolute abundances of iARGs,aeARGs and feARGs increased by-0.98～3117.79,-0.83～30.26 and-0.97～5.23 times,respectively.Compared with that in the control,the trend of iARGs increased while feARGs exhibited a decreasing trend.0.05 mg/L and 50 mg/L nm-PS promoted the proliferation of iARGs and aeARGs,while feARGs was inhibited at 50 mg/L μm-PS exposure.(3)When exposed to the high concentration of nm-PS(50 mg/L),the production of ROS increased to 1.16 times of the initial level,and the proportion of living cells decreased by 16%;After exposure to PS,The expression amount of multidrug efflux genes(acr A)decreased by 2%～85%;The absolute abundance of class 1 integron(int1)increased107.09 times under 50 mg/L mm-PS exposure,which represent the frequency of horizontal gene transfer.Among them,the adsorbed int1 had the greatest increases(107.09);When exposed to nm-PS,the number of bacterial community increased significantly(186～193),in which Proteobacteria and Bacteroidota accounted for the main position.(4)Correlation analysis showed that the overproduction of ROS promoted the proliferation of ARB,while the decrease of the proportion of living cells inhibited the growth of ARB;The abundance of int1 gene was significantly correlated withARGs.The proliferation of intracellular and adsorbed int1 significantly promoted the spread of iARGs and aeARGs,while the absolute abundance of feARGs decreased with the increase of free int1;Proteobacteria and Bacteroidota was potential hosts harboringARGs in the environment.