Biofilm Structural and Functional Features on Microplastic Surfaces in Greenhouse Agricultural Soil

Abstract

Microplastics (MPs) enter the soil through a variety of pathways, including plastic mulching, sludge, and organic manure application. In recent years, domestic and foreign experts and scholars have been concerned about the residues and contamination of MPs in the soil of greenhouse agriculture. In this investigation, five types of MPs including low-density polyethylene (LDPE), high-density polyethylene (HDPE), polystyrene (PS), polypropylene (PP), and polyethylene terephthalate (PET), and two concentrations (1% and 5%, w/w) were used in a 30-day external exposure test. Evidence of microbial enrichment was found on the surface of the MPs. The total amount of biofilm on the surface of MPs increased dramatically with increasing exposure time and MP concentrations. The polysaccharide content of extracellular polymers (EPS) in biofilms was significantly different, and the maximum PS1 (1% (w/w) PS) concentration was 50.17 mg/L. However, EPS protein content did not change significantly. The dominant bacteria on the surface of MPs with different types and concentrations were specific, and the relative abundance of Patescibacteria was significantly changed at the phylum level. At the genus level, Methylophaga, Saccharimonadales, and Sphingomonas dominated the flora of LDPE1 (1% (w/w) LDPE), PS1, and PET5 (5% (w/w) PET). The dominant bacteria decompose organic materials and biodegrade organic contaminants. According to the FAPROTAX functional prediction study, chemoheterotrophy and aerobic chemoheterotrophyplay a role in ecosystem processes such as carbon cycle and climate regulation. The application of LDPE1 has a greater impact on the carbon cycle. Plant development and soil nutrients in greenhouse agriculture may be influenced by the interaction between MPs and microorganisms in the growing area, while MP biofilms have an impact on the surrounding environment and pose an ecological hazard.

Some Microbiological Characteristics of the Biofilm on the Surface of Pre-Production Pellets of Polypropylene Microplastics after Short Exposure in Soil

“…Chen et al [8] established that the biomass of the biofilm is higher on the 30th day than on the 15th day. In general, inhabitation of the microplastic surface by microorganisms occurs within hours, and on the 14th day, the biofilm is fully formed [20].…”

“…The biological activity of microorganisms on polymeric materials that enter the soil, in particular as garbage, leads to biofilm formation and initialization of material biodegradation occurs [7,8]. Among soil microorganisms, as biodegraders of synthetic polymers, heterotrophic bacteria and sulfate-reducing bacteria (SRB) deserve attention since they are part of the plastisphere and are able to form a biofilm on the surfaces of plastics [8][9][10][11][12]. The aim of this study was to investigate some chemical and microbiological characteristics of the soil and the surface biofilms of both polypropylene microplastics and quartz sand.…”

Genetic Basis and Expression Pattern Indicate the Biocontrol Potential and Soil Adaption of Lysobacter capsici CK09

“…Extensive surfaces, such as soil particles, root surfaces, fungal hyphae and microplastics, dominate in agriculture soil [ 88 , 89 , 90 ]. The colonization and biofilm formation of bacterial cells on surfaces in soil allow them to utilize higher concentrations of nutrients, to develop a greater diversity and evenness in the microbial community, to induce elevated metabolic activity and to protect bacterial cells from stresses such as toxic compounds [ 88 , 91 ].…”

Recent advances in the relationships between biofilms and microplastics in natural environments

“…In the reviewed literature, indirect quantification of biofilms on MPs surfaces is commonly used. Crystal violet staining is a commonly used method that provides straightforward results due to its capacity to bind to negatively charged components of bacteria and extracellular polymeric substances (Tu et al 2020 ; Chen et al 2022 ). Another frequently used method based on spectrophotometric measurements is the determination of biofilm polysaccharide and protein content, which are positively correlated with biofilms (Misic and Covazzi Harriague 2019 ; Ganesan et al 2022 ; Chen et al 2022 ).…”