Study On The Combined Toxicity Of Polylactic Acid Microplastics And Copper Ions On Bacillus Amyloliquefaciens

As one of the new pollutants,microplastics can be transported to every corner of the world by means of atmospheric circulation and water movement,and show varying degrees of toxicity to animals,plant and algae simultaneously.But biodegradable plastics currently on the market instead form microplastics more quickly without reducing the toxic impact on living beings.In addition,due to the hydrophobicity of microplastics,the co-existing contaminant copper in the environment is more likely to be adsorbed on its surface and transported with it.Some studies have shown that the combined action of microplastics and heavy metals increases the toxicity to organisms.There is also a contrary view that the adsorption of microplastics reduces the bioavailability of heavy metals,so it is very necessary to explore the combined toxicity of biodegradable plastics and copper.Moreover,owing to the ability to produce bacteriostatic and growth-promoting substances,Bacillus amyloliquefaciens has a wide range of applications in agricultural production,food processing and preservation,medicine and environmental protection.Therefore,this experiment intended to study the alone and combined toxicity of polylactic acid microplastics(PLA MPs)and copper ions on Bacillus amyloliquefaciens.The specific research content included two parts: macro-index analysis and transcriptome analysis.Deeply explore the toxicity mechanism and the influence of pollutants on the application of Bacillus amyloliquefaciens.The experimental results showed that:(1)During the three-day experiment,PLA MPs alone inhibited the growth of 21.2%-27.5% of the bacterial,destroyed the protein and teichoic acid components in the cell wall,and induced CAT to scavenge free radicals,but basically had no effect on the cell membrane.(2)Under the combined action,the toxicity to the bacteria was significantly increased,the two pollutants inhibited the growth of 20.1%-43.6% of the bacteria,and damaged proteins,teichoic acid and peptidoglycan components.Cell membrane lipid peroxidation was serious.In addition,PLAMPs promoted adsorption and accumulation of copper ions in the bacteria.But the two pollutants were not simple additive or synergistic effects.(3)Transcriptome analysis found that PLA MPs alone reduced the expression of genes related to thiamine and their derivatives,forced the reduction of the antioxidant capacity of the bacteria,and at the same time up-regulated the expression of genes related spore formation.While the combined pollutants accelerated the expression of genes related to the synthesis and transport of inorganic cationic transmembrane proteins to relieved toxicity through chelation and efflux of copper ions,and meanwhile,reduced the expression of genes related to indole derivatives to promote the formation of cell membranes to resist stress.(4)In addition,copper ions instead increased the gene expression of fengycin,iturin and spermidine,which improved the bacteriostatic activity and also promoted plant growth.Above all,PLA MPs had little effect on the bacteria and might increase the toxicity of copper ions.However,the regulatory mechanisms triggered by Bacillus amyloliquefaciens were not completely consistent when they were stressed by pollutants.Therefore,in the future,further consideration should be given to the impact of biodegradable plastics and other pollutants on organisms under actual environmental conditions.