Abstract:

As a type of emerging pollutants, microplastics have become pervasive contaminants affecting ecosystem safety and human health. Microbial biodegradation of microplastics has attracted significant attention due to its environmentally friendly and sustainable attributes. Recent advancements have been achieved in the microbial biodegradation of pollutants through biofilms, enzyme engineering, and gene regulation. Biofilms influence the microplastics degradation by altering surface properties, leaching additives, enzyme or radical attacks, and permeation decomposition. Extracellular enzymes cleave the macromolecular structures, while intracellular enzymes modify substrate structures and process metabolites. Current research focuses on constructing highly efficient enzyme systems. Genetic engineering has enabled the cultivation of engineered bacteria, while bioinformatics aids in identifying functional genes and elucidating the degradation pathways. Metagenomic modification has been used to enhance biodegradation efficiency. This article reviews recent progress in microbial biodegradation of microplastics, encompassing diverse degrading microorganisms, clear degradation metabolic pathways and mechanisms. Multiple microorganisms including bacteria, fungi, and microalgae possess degradation capabilities. Composite microbial consortia synergistically drive the degradation process. Bacteria mainly degrade microplastics by secreting hydrolases and oxidases, which can break the macromolecular chains or change the chemical structure of plastics. Fungi, on the other hand, rely on the secretion of intracellular and extracellular enzymes as well as biological surfactants to break down microplastics into monomers. The mycelium can also enhance the degradation effect. Microalgae can promote degradation by means of photosynthesis, secreting toxins, enzymes, and extracellular polymeric substances. Microplastic degradation typically occurs in four stages: bio-deterioration, fragmentation, assimilation, and mineralization. Different microorganisms exhibit varying efficiencies and mechanisms for microplastics degradation such as polyethylene and polystyrene. By summarizing current research findings, this review provides a theoretical foundation for further in-depth exploration of microbial biodegradation mechanisms and offers potential methods and techniques for eliminating the microplastics in the environment.

Key words: microplastics, microbial biodegradation, metabolic pathways, degradation mechanisms