The Effect Of Nanoplastics And Multi-walled Carbon Nanotubes Exposure On The Growth Of Microcystis Aeruginosa

Recently,plastics and carbon nanotubes have been widely used in various fields such as daily chemicals,medical treatment,biology,sensors,and catalytic degradation because of their good physical and chemical properties.Due to the improper disposal,they entered the water environment as the emerging pollutants.The toxic effects of micro/nanoplastics and carbon nanotubes on animals,plants and microbes have been extensively demonstrated,but there has been no study exploring the potential ecological risks of combined exposure of micro/nanoplastics and carbon nanotubes.Therefore,based on the general biological toxicity that may exist,this study chose the more widely used polystyrene nanoplastics(Nano-PS)and multiwalled carbon nanotubes(MWCNTs)as the research objects,the dominant species of cyanobacteria blooms-Microcystis aeruginosa(M.aeruginosa)as the object to exposure.This study deeply explored the toxic mechanism by the joint analysis of physiological properties and transcriptomics in the individual and co-exposure of Nano-PS and MWCNTs.What’s more,this could made up for the deficiency of current research on combined exposure of these two nanoparticles and their toxic mechanism,and also provided reference for the water environmental risk awareness as well as the safety management of plastic and carbon nanotube products.The specific work of this research mainly includes the following three parts.(1)The effect of Nano-PS individual exposure on the growth of M.aeruginosa and its toxic mechanism.By analyzing the changes in cell density,chlorophyll a,total protein content,SOD activity,and MDA content during the 15-day continuous exposure of the Nano-PS,combined with the electron microscope images and transcriptomics of the cells after 15 days of exposure,the algal cytotoxicity of NanoPS was analyzed.The results showed that Nano-PS exposure could promote the growth of M.aeruginosa in a low concentration(5 mg/L).Other concentrations showed an inhibitory effect,and all stimulated the oxidative stress.Cell deformation even broken could be observed under the electron microscope.From a genetic point of view,genes related to cell photosynthesis have been downregulated,while the expression of related genes such as ribosomes and translation processes has been upregulated.This was contrary to the inhibitory effect of total protein content,which may be caused by the selective upregulation of ribosomes.In order to offset the inhibitory effect caused by the down-regulation of a large number of t RNA-related genes,and supplement inactive and denatured proteins to maintain normal cell activities,indicated that Microcystis aeruginosa has made a positive response to the external Nano-PS stress.(2)The effect of MWCNTs individual exposure on the growth of M.aeruginosa and its toxic mechanism,the analysis method was the same as that of the Nano-PS exposure.MWCNTs could also promote the growth of M.aeruginosa in the low concentration,and other concentrations inhibited,and the inhibitory effect was significantly stronger than that of Nano-PS.The oxidative stress effect was also significantly higher than that of the Nano-PS,which 20 mg/L treatment group had the highest SOD activity,while the 50 mg/L treatment group was at a lower level throughout the growth period.This may be due to the inhibition of the cellular antioxidant system at the initial stage of exposure.Electron micrographs showed that the cells were obviously deformed or even damaged,the cell wall and the protoplasm layer were separated,the layered thylakoids within the cells were dissolved,and the cell transparency increased.Through the GO(Gene Ontology)and KEGG(Kyoto Encyclopedia of Genes and Genomes)enrichment analysis of the differential genes,various ion transport-related genes were downregulated,while a variety of cell metabolism and biosynthetic process-related genes were upregulated,and the cell metabolism process was accelerated.The positive regulation made by external stress could continuously provided new energy by accelerating cell metabolism and metabolize damaged tissues to maintain normal cell life activities.(3)The effect of co-exposure of Nano-PS and MWCNTs on the growth of M.aeruginosa and their toxic mechanism.The results showed that the inhibition of cell growth and oxidative damage in the co-exposure group decreased with the increase of the exposure concentration.The co-exposure of the two nanoparticles showed an antagonistic effect,and it increased with the increase of the concentration.This may be due to the stronger agglomeration effect at high concentrations,which reduced the contact between nanoparticles and algae cells,and reduced the biological toxicity of the experimental system.Among the different expressed genes(DEGs),the number of DEGs in the co-exposure group was significantly lower than that in the individual exposure,showing the weakest biological toxicity,with MWCNTs being the strongest,followed by the Nano-PS.The results of the GO and KEGG enrichment analysis showed that combined exposure slightly promoted cell photosynthesis,but disrupted cell homeostasis,ion balance and amino acid metabolism.In this study,we studied the biological toxicity and toxic mechanism of nanoplastics and carbon nanotubes by comparing the physiological properties and transcriptome analysis of M.aeruginosa exposed by the individual and co-exposure of these two completely different forms nanoparticles,and the potential ecological risks of water environment that may exist in their joint exposure,providing reference for the safe production and management of plastics and carbon materials.