Microplastic-enriched Biofilms In Facility Soils And Their Impact On Soil Microbial Communities

Plastics are widely used in daily life and industrial activities due to their low cost,high durability,and portability.Plastics are exposed to the environment and undergo ultraviolet radiation,collision wear,hydrolysis,soil erosion or biological effects to form solid particles with a particle size of less than 5 mm,called microplastics(Microplastis,MPs).The issue of MPs residue and pollution in protected farmland soil has attracted extensive attention from relevant domestic experts and scholars in recent years,but there are still gaps in the law of biofilm succession on the surface of MPs,ecological risks,and the interaction between MPs-degrading bacteria and the protected farmland soil environment.This study investigates the accumulation of MPs in protected farmland soil,and analyzes the surface biofilm structure,microbial community succession and potential functional characteristics of microbial communities.Using MPs as the only carbon source to enrich,isolate,purify and screen microbial degrading bacteria,and study the effects of single and mixed MPs degrading bacteria on the physical and chemical properties and microbial communities of MPs-contaminated soil.Below are key research findings:1.The survey results of MPs pollution in the soil of 17 facility farmlands showed that the abundance of plastics in the facility farmland soil was about 300-2750 pieces/kg,of which MPs with a particle size of less than 5 mm accounted for 61.14%,while the particle size of 2-4 mm The proportion reached 34.45%.The types of MPs in protected farmland soil are mainly polyethylene,polypropylene and polyester,mainly concentrated in pH 6.5-7.5,nitrate nitrogen content greater than 150 mg/kg,available potassium content 50-100 mg/kg,available phosphorus In soils with a content greater than 40 mg/kg and an organic matter content of 10-20 g/kg.The abundance of MPs in the soil was related to the use of fertilizers,cultivation years and fallow conditions,among which the MPs with a growth period of 20 years were the most polluted.The results of Pearson analysis showed that the abundance of MPs was related to soil pH,nitrate nitrogen,available phosphorus,organic matter and available potassium content.2.According to the 1%and 5%of the dry weight of the soil,5 different MPs were applied for 30 days of soil culture experiments.Microbes were enriched on the surface of MPs.The total amount of biofilm on the surface of MPs increased significantly with the increase of culture time and MPs abundance.The polysaccharide content of extracellular polymers in the biofilm was significantly different.The polysaccharide content of ethylene was the highest,reaching 50.17 mg/L;while the protein content of extracellular polymers had no significant difference,both were above 30 mg/L.The dominant bacteria on the surface of different types and abundances of MPs were specific,and the relative abundance of Patescibacteria changed significantly.MPs biofilm has unique dominant flora,the dominant flora of 1%abundance low-density polyethylene,1%abundance polystyrene,5%abundance polyethylene terephthalate are Methylophage,Saccharimonadales,Sphingomonas sp.FAPROTAX functional prediction analysis showed that chemoheterotrophs and aerobic chemoheterotrophs were the two most abundant functional groups in all soil samples,and the proportions of methoxylation and methanol oxidation increased with time.The enrichment of heterotrophic bacteria on MPs indicates that bacteria mainly obtain carbon and energy by oxidizing organic compounds,and participate in important ecological functions of carbon cycle.3.With LDPE and PET as the sole carbon source,8 strains were screened out,namely bacteria(BL1 strain,BL2 strain)and fungi(FL1 strain,FL2 strain)that can degrade LDPE,and bacteria that can degrade PET(BP1 strain,BP2 strain).strains)and fungi(FP1 strain,FP2 strain).After 28 days of degradation experiments,the degradation rate of BL2 strain among the bacteria degrading LDPE was the highest,reaching 13.07%,and the degradation rate of FL1 strain among fungi was the highest at 15.24%;The highest strain degradation rate was 8.35%.Through scanning electron microscope characterization,it was found that MPs degrading bacteria increased the surface roughness of MPs and increased the loss of MPs mass.The specific surface area of LDPE was reduced by 1.93m2/g at most when treated with FL1 strain,and the minimum pore size was 2.87 nm.The specific surface area of PET was reduced when treated with BP1 strain.The maximum is 1.29 m2/g,and the minimum pore size is 2.45 nm.FT-IR analysis showed that the specific characteristic peak vibration index of LDPE and PET changed,indicating that the inoculation of degrading bacteria led to changes in the chemical functional groups of MPs.By measuring pH,OD540 and protein content,it was concluded that 14 days was the best time for the growth of degrading bacteria,and the degradation efficiency of degrading bacteria was high.16S rRNA sequencing of BP1 strain,BL2 strain,FP2 strain and FL1 strain showed that BP1 strain was Bacillus subtilis,BL2 strain was Ensifer adhaerens,and FP2 strain was Aspergillus fumigatus and FL1 strains are Aspergillus sp.4.Based on high-throughput sequencing and comparative analysis of soil physical and chemical properties,the effects of LDPE microplastic-degrading bacteria cultured in soil for 14 days on soil physical and chemical properties and microbial community structure and diversity in soil were studied.A total of 4 treatments were designed with 5%LDPE,5%LDPE+BL2(only BL2 strain added),5%LDPE+FL1(only FL1 strain added)and 5%LDPE+ML(add BL2 and FL1 strains).The treatment of LDPE-degrading bacteria led to a decrease in bacterial abundance,a decrease in diversity,and an increase in richness;an increase in the abundance of fungal communities,a decrease in diversity,and a decrease in richness.The treatment of LDPE-degrading bacteria led to the largest increase in the relative abundance of Proteobacteria and Mucoromycota among bacteria,and increased the endemic fungi Eukaryota_norank and Chytridiomycota.The dominant bacterial genera of 5%LDPE+FL1 and 5%LDPE+ML were Vicinamibacteraceae_norank,Vicinamibacterales_norank,and Methyloversatilis,etc.,and the dominant fungal genera were Fusarium,Chaetomium,and Remesonia,etc.The degradation effect of FL1 strain played a dominant role in the mixed bacteria ML treatment.The results of RDA analysis showed that EC,TP and pH in the bacterial community were the most important influencing factors in the two treatments of 5%LDPE+BL2 and 5%LDPE+FL1,and in the fungal community TN and TP were the degrading bacteria of 5%LDPE+FL1 The most important influencing factor,EC is the most important influencing factor of 5%LDPE+BL2 degrading bacteria and 5%LDPE+ML degrading bacteria.Effects of PET microplastic-degrading bacteria cultured in soil for 14 days on soil physical and chemical properties and microbial community structure and diversity in soil.A total of 4 treatments were designed by applying 5%PET,5%PET+BP1(adding only BP1 strain),5%PET+FP2(adding only FP2 strain)and 5%PET+MP(adding BP1 and FP2 strains).The minimum EC value of 5%PET+FP2 was 14.9 mS/m,and the maximum TN and TP values were 268.6 mg/kg and 459.7 mg/kg.The treatment of PET-degrading bacteria led to an increase in the diversity of the bacterial community and a decrease in the richness;and an increase in the richness and diversity of the fungal community.The 5%PET+BP1 and 5%PET+FP2 treatments resulted in the largest increase in the relative abundance of Acidobacteriota in bacteria,and the 5%PET+MP treatment resulted in the largest increase in the relative abundance of Proteobacteria in bacteria.The fungus Ascomycota all increased after PET-degrading bacteria treatment.After treatment with PETdegrading bacteria,the same dominant bacterial genera were Vicinamibacteraceae_norank and Methylophilus,and the same dominant fungal genera were Chaetomium,Remersonia,Fusarium,and Mortierella.Different PETdegrading bacteria treatments had similar effects on the soil microbial community,and the degradation efficiency of the mixed bacteria MP strain was higher than that of the BP1 strain and FP2 strain.According to the RDA analysis,EC,TP and pH are the most important influencing factors in the 5%PET+FP2 degrading bacteria in the bacterial community,while TN is the most important influencing factor in the 5%PET+BP1 degrading bacteria.In the fungal community,TN and TP is the most important influencing factor in 5%PET+FP2 degrading bacteria.