Microbial Platform for Tailor-made Production of a Biodegradable Polylactide Modifier: Ultrahigh-Molecular-Weight Lactate-Based Polyester LAHB

Abstract

Polylactide (PLA) is a biobased synthetic polyester with diverse commercial applications. Nevertheless, PLA has been deemed unfavorable owing to its constrained processability, impact resistance, and biodegradability. Therefore, this study aimed at engineering novel biodegradable modifiers based on a highly chiral enantiopure D-lactate (D-LA)-based polyester called poly[D-LA-co-(R)-3-hydroxybutyrate (3HB)] (LAHB) to improve the physical properties of PLA. High-molecular-weight (hmw) LAHB was synthesized from the chemoautotrophic Cupriavidus necator in substantial quantities. The tailor-made overproduction of LAHB was achieved by using a minimal medium containing glucose and retaining the intrinsic synthetic pathway for the 3HB homopolymer in C. necator, which produced the highest yields, reaching up to 27 g/L/48 h. The molecular weight of LAHB substantially elevated up to 1.1 × 106 g/mol and was termed ultrahigh-molecular-weight (uhmw) LAHB. The LA faction in LAHB was modulated via a synergistic optimized combination of the lactate dehydrogenase and propionyl-coenzyme A transferase variants as well as by effective shut-off of the D-LA escape route. Combination of PLA and the two selected biodegradable uhmw-/hmw-LAHBs as demand-oriented biodegradable modifiers allowed improved processability and impact resistance of PLA while retaining transparency. These benefits of LAHB are distinguishable from those of conventional biobased modifiers, including 3HB-based polymers.