Microbial Degradation of Polystyrene: Mechanisms, Enzymes and Environmental Significance

Polystyrene (PS) is a widely used synthetic plastic known for its durability, low cost, and versatility; it is easily available in the market. Despite its numerous advantages, the increasing PS accumulation results in serious environmental contamination that greatly adds to the world’s plastic waste problem. Common variants of PS, such as high-impact polystyrene (HIPS), expanded polystyrene (EPS) and general-purpose polystyrene (GPPS), endure in ecosystems and, during degradation, emit detrimental chemicals, microplastics, and nanoplastics that adversely impact soil, water, and living organisms. Biodegradation using microorganisms has emerged as a sustainable alternative to conventional disposal methods like landfilling and incineration. Various microorganisms, including both fungi and bacteria, have the ability to degrade PS. These microorganisms secrete enzymes (e.g., laccase, esterase, lipases, and monooxygenases), which initiate a series of biochemical reactions that convert PS into non-toxic compounds, such as CO2 and H2O. Analytical techniques like depolymerase assay, biofilm formation assay, Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) and Gas chromatography-mass spectroscopy (GC-MS) were employed to study these biodegradation processes and monitor the physical and chemical changes in polymer structure during microbial activity. This review highlights the potential role of microorganisms and their enzymes in managing PS waste to mitigate environmental pollution and facilitate the transition to a circular economy.