Tough and biodegradable lactate (LA)-based polyester (LAHB) hyperproduced by reinforcing LA-polymerizing enzyme gene expression

• Established a rational design strategy that relieved the polymerization bottleneck in LAHB biosynthesis using Cupriavidus necator • Demonstrated record-highest LAHB production (97 g/L DCW; 68 g/L polymer in 48 h). • Enhanced lactate incorporation while maintaining high molecular weight through fine-tuned LPE expression level. • Achieved the production of LAHB with balanced strength and elongation, exhibiting toughness comparable to polyethylene. Poly[( d -lactate)- co -( R )-3-hydroxybutyrate] (LAHB) is a microbial copolyester that exhibits excellent environmental biodegradability. LAHB also functions as a multifunctional modifier that markedly improves both the mechanical properties and biodegradability of non-biodegradable poly(L-lactide) (PLLA). The lactate (LA) fraction is a key determinant governing the material properties of LAHB as well as its d -LA-L-LA-mediated interactions with PLLA. Then, in this study, we attempted to reinforce the gene expression of lactate-polymerizing enzyme (LPE) in the recombinant strain of Cupriavidus necator that was plausibly to be a rate-limiting factor for LA-unit incorporation. Expectedly, with the improved LA fraction, high-cell-density cultivation of the engineered strain GSXd147 synergistically achieved 97 g L⁻¹ dry cell weight and 70 wt% LAHB within 48 h from glucose—the highest LAHB titer and productivity reported to date. It should be noted that the resulting LA-enriched LAHB retained a high-molecular weight (15 mol% LA, M w 30 × 10 4 ) and consequently exhibited a well-balanced combination of strength and elongation, yielding overall toughness comparable to the petroleum-based polyethylene.