Environment-driven regulation of EPS secretion and interfacial coupling in microalgae-microplastic hetero-aggregates: Insights from molecular mechanisms to utilization potential.

Microplastics (MPs), as emerging pollutants, have been increasingly detected in aquatic ecosystems, where their interactions with microalgae critically influence pollutant transport and ecological risks. This study aimed to elucidate how different nutrition levels and MPs types regulate extracellular polymeric substance (EPS) secretion and hetero-aggregation behavior of Scenedesmus sp. A combination of experimental observations and density functional theory (DFT) simulations was used to investigate the interfacial interactions between Scenedesmus sp. and two representative microplastics, polystyrene (PS) and polyvinyl chloride (PVC), while metabolomic profiling was conducted to examine the corresponding biochemical responses. Results showed that PS exposure induced the formation of larger and looser flocs with a maximum sedimentation efficiency of 99.63%, whereas PVC resulted in smaller and denser aggregates (93.57%). DFT analysis further demonstrated that PS-EPS interactions were dominated by delocalized van der Waals and hydrogen-bonding forces, whereas PVC-EPS complexes involved localized polar interactions mediated by proteinaceous EPS. Metabolomic analysis indicated that both PS and PVC disturbed purine metabolism and lipid remodeling, with PVC additionally activating amino acid and nitrogen metabolic pathways. Overall, nutrition levels and MPs types jointly modulated EPS composition, interfacial coupling, and aggregation characteristics. This study provides molecular-level evidence for understanding the interfacial mechanisms between microplastics and microalgae. The resulting hetero-aggregation could be further utilized for biodiesel production, enabling the valorization and conversion of waste materials.