Co-metabolism of microplastics and organic substrates by environmental microbes: Chemical mechanisms and bioprocess strategies

Microplastic pollution has emerged as a global environmental concern due to its persistence, ecological toxicity, and resistance to degradation. While microbial biodegradation offers a promising solution, the efficiency and scope of microplastic degradation when used as a sole carbon source remain limited. Co-metabolism, in which environmental microbes degrade non-growth substrates like microplastics in the presence of additional organic compounds, has gained increasing attention as an effective strategy to enhance plastic degradation. This review provides a comprehensive synthesis of current knowledge on co-metabolic degradation of microplastics by bacteria and fungi, with particular emphasis on the chemical mechanisms, key enzymatic pathways, and system-level optimization strategies. We highlight the role of organic co-substrates in stimulating enzyme production, supporting microbial growth, and facilitating the breakdown of otherwise recalcitrant polymer chains. The review also examines critical parameters affecting co-metabolic efficiency, including substrate ratios, environmental conditions, and bioreactor configurations. Despite promising advances, challenges remain in understanding pathway regulation, intermediate toxicity, and microbial interactions within complex communities. Finally, we discuss future directions involving omics-driven discovery, synthetic microbial consortia, and AI-based modeling to accelerate innovation in sustainable microplastic remediation. This review aims to bridge microbiology, environmental chemistry, and bioprocess engineering toward a more circular plastic economy.