Microbial Biodegradation of Plastics and Microplastics: Enzymatic Mechanisms, Biotechnological Applications, and Ecotoxicological Perspectives

The global rise in plastic production has resulted in extensive environmental accumulation and fragmentation into microplastics and nanoplastics. These persistent particles are now found in aquatic, terrestrial, and atmospheric ecosystems, posing ecotoxicological risks by transporting toxic chemicals, disrupting microbial communities, and entering the food chain, with potential human health impacts. Biodegradation by microorganisms has therefore gained attention as a sustainable remediation strategy. This review examines the role of microorganisms in degrading plastic and microplastics, focusing on enzymatic mechanisms, biotechnological applications, and associated risks. Bacteria such as Ideonella sakaiensis, Pseudomonas, Bacillus, and Rhodococcus exhibit strong degradative abilities via PETase, MHETase, cutinases, and oxidases, often enhanced by biofilm formation. Fungi, including Aspergillus and Penicillium, as well as microalgae, contribute through the production of extracellular enzymes and synergistic interactions. Environmental conditions—such as temperature, pH, salinity, and oxygen levels—directly influence microbial activity and enzyme performance. Biotechnological approaches have improved degradation efficiency through microbial consortia, genetic engineering, and omics-based discovery of novel enzymes. Laboratory-scale applications, including bioreactors and nanoparticle-assisted systems, have achieved higher degradation rates compared to single strains. However, major limitations persist, including microbial stability in natural environments, scalability, and the toxicity of degradation intermediates such as terephthalate and ethylene glycol. Overall, microbial biodegradation offers a promising alternative to conventional treatments but requires careful evaluation of ecological safety and economic feasibility. This review emphasizes the importance of interdisciplinary strategies combining microbiology, biotechnology, and environmental toxicology to advance plastic biodegradation and support sustainable waste management.