Breaking upstream–downstream linkage obstacles for efficient, economical, and green production of high-molecular-weight poly(β-L-malic acid)

Abstract Background Poly(β-L-malic acid) (PMA) is a biodegradable, biocompatible, and chemically modifiable polymer with broad applications. However, the production of high-molecular-weight, high-purity PMA (hhPMA) has long been constrained by “upstream–downstream linkage obstacles”, resulting in relatively low yield, high cost, and significant environmental burden. To address this issue, we systematically reconstructed the hhPMA production chain, establishing an integrated green chain covering the upstream, midstream, and downstream stages. Results In the upstream stage, we isolated a high-performing strain ( Aureobasidium pullulans 389) for hhPMA from Hevea brasiliensis , which inherently produces high titers of PMA with a dominant high-molecular-weight fraction, and systematically engineered it by reducing by-product biosynthesis, enhancing precursor supply, and balancing cofactors, thereby improving PMA synthesis further. In the midstream stage, a mixed-substrate strategy combining refined sugars with H. brasiliensis sawdust hydrolysate reduced refined carbon and nitrogen inputs by ~ 85% and ~ 100% in shake flasks, and achieved a PMA titer of ~ 260 g/L in a 5-L bioreactor. In the downstream stage, a green separation process integrating CaCO₃ recycling, anion-exchange resin adsorption, and ultrafiltration achieved an overall PMA recovery of > 90%, with > 95% recovery and nearly 99% purity for the ≥ 20 kDa fraction, minimizing Ca-containing wastewater and eliminating solvents. Conclusions This study systematically reconstructed the hhPMA production chain through coordinated upstream strain engineering, midstream mixed-substrate fermentation, and downstream green purification. The reconstructed production chain overcomes “upstream–downstream linkage obstacles,” enabling a more efficient, economical, and green hhPMA manufacturing process from lignocellulosic biomass of H. brasiliensis wood. These findings offer a valuable reference for the production of hhPMA and related organic acids/biopolymers in A. pullulans .