Metabolic Process and Mechanistic Model of White-Rot Fungi Degrading Plastic Films by Solid-State Fermentation

Recent studies have demonstrated the capacity of white-rot fungi to degrade nonoxygen-containing plastics, yet how it occurs for oxygen-containing (O-containing) in solid-state fermentation system remains unclear. In this study, we systematically evaluated the biodegradation pathways of O-containing plastic films, including two commercially compostable plastics (compostable plastic and starch-based compostable plastic) and two self-prepared plastics (polylactic acid (PLA) containing 1% oxalic acid and PLA containing 0.1% oxalic acid), by co-cultivation with Phanerochaete chrysosporium under solid-state fermentation (SSF). SSF promoted plastic depolymerization and mineralization by coupling an oxidative microenvironment with fungal metabolic and co-metabolic activity. Interestingly, we found that O-containing plastic films perform two steps in degradation: 1) extracellular hydrolytic and oxidative cleavage of ester bonds, generating low-molecular-weight oligomers and monomers; 2) intracellular assimilation and metabolic conversion of these intermediates into central carbon metabolism, ultimately leading to mineralization. In particular, two compostable plastics exhibited similar degradation rates due to their comparable intrinsic structures, while high concentrations of oxalic acid enhance PLA oxidation and acid-catalyzed hydrolysis, promoting ester bond cleavage and resulting in significantly higher biodegradation efficiency. Meanwhile, key functional genes related to oxidation and hydrolytic metabolism (such as alcohol oxidase, aldehyde dehydrogenase, aconitate hydratase, and members of the short-chain dehydrogenase (SDR) family) showed high expression levels. Among them, compared to studies on nonoxygen-containing plastics, the SDR family genes were significantly upregulated 28-fold. Combined with nonoxygen-containing plastics degradation pathway, these results provide new insights in mechanistic modeling for the degradation of O-containing plastic films.