Toxic Effects And Mechanism Of Two Nanoparticles On Paramecium Bursaria-Chlorella Symbiotic System

Symbiosis is a common phenomenon in nature,and the maintenance of normal symbiosis between organisms is very important to the balance of ecosystem.Many studies have confirmed that nanoparticles have toxic effects on organisms,their biological effects and toxic mechanisms have been explored,but the effects on symbiotic organisms in nature still unclear.Therefore,Paramecium bursariaChlorella symbiotic system,was selected as the research object,and the widely used bactericidal silver nanoparticles(Ag NPs)and copper nanoparticles(Cu NPs)were represented in this paper to explore the biological effects of nanoparticles on the symbiotic system from the perspectives of ultrastructure,enzyme activity,transcriptome,ect.Firstly,the acute toxicity of P.bursaria was measured with two nanoparticles at different concentrations,the effects and the damage degree of nanoparticles on the ultrastructure of P.bursaria cells were observed at the concentration of LC50.Then,the effects of nanoparticles on cell physiology and biochemistry were detected by fluorescence labeling and enzyme activity assay,and the toxicity mechanism was preliminarily analyzed based on the experimental results.Finally,transcriptome technology was used to explore the molecular mechanism of biological effects of nanoparticles,and the reasons for the effects on the stability of the symbiotic system were analyzed.The main results are as follows:1.Toxic effects of nanoparticles on P.bursaria-Chlorella symbiotic systemThe results of acute toxicity test showed that the two nanoparticles both had strong biological toxicity to P.bursaria,and could inhibit cell proliferation or even cause its death at low concentration.The half-maximal inhibitory concentration of Ag NPs and Cu NPs were 0.3 mg/L and 0.047 mg/L,respectively,which could lead to cell death at low concentrations,and the toxicity of Cu NPs to P.bursaria was stronger than that of Ag NPs.Energy spectrum analysis showed that nanoparticles could be detected in the cells of P.bursaria after exposure to nano-solution.Both kinds of nanoparticles can cause damage to the surface and internal ultrastructure of cells,including cilia shedding,membrane damaging,mitochondrial swelling,nucleolar of nuclear deformation,etc.The damage of Cu NPs on the structure of cells is more serious than that of Ag NPs.Besides,transmission electron microscopy showed that a large number of symbiotic chlorella were digested,suggesting that the nanoparticles might affect the stability of the symbiotic system between P.bursaria and Chlorella.Reactive oxygen species(ROS)labeling and enzyme activity changes confirmed that nanoparticles could lead to oxidative stress in P.bursaria-Chlorella symbiotic system.Excessive ROS accumulated in the symbiotic system,and the related enzyme activities showed an upward trend.The results of fluorescence labeling showed that oxidative stress occurred in both host and symbiotic algae cells after nanoparticles treatment,and the digestion activity in the symbiotic system was enhanced.2.Transcriptome study of P.bursaria-Chlorella symbiotic system after exposure to copper nanoparticlesThe transcriptome detected 545 and 120 differentially expressed genes in P.bursaria and Chlorella,respectively,and the analysis of related enrichment pathways preliminarily confirmed that the exposure of Cu NPs mainly result oxidative stress and energy metabolism disorder in host and symbiotic algae cells.Cell damage caused by oxidative stress is one of the main ways that the nanoparticles produce toxicity to organisms,and the disorder of energy metabolism may be caused by the excessive energy consumption of cells for antioxidant activities and repair of damaged structures.In conclusion,similar to non-symbiotic organisms,nanoparticles can induce oxidative stress in both P.bursaria and Chlorella cells in the symbiotic system,and damage the surface and internal ultrastructure of cells.At the same time,the stability of the symbiotic system is affected,which may be caused by the increased energy consumption of cells under stress,the host uses digestive Chlorella instead of autophagy in non-symbiotic cells.This study is first to reveal the toxic effects of nanoparticles on ecosystem symbiosis and provided new data for further study of environmental effects and toxicological mechanisms of nanoparticles.