Biosynthesis of novel lactate-based polymers containing medium-chain-length 3-hydroxyalkanoates by recombinant Escherichia coli strains from glucose

Abstract

Novel lactate (LA)-based polymers containing medium-chain-length 3-hydroxyalkanoates (MCL-3HA) were produced in fadR-deficient Escherichia coli strains from glucose as the sole carbon source. The genes encoding LA and 3-hydroxybutyrate (3HB) monomers supplying enzymes [propionyl-CoA transferase (PCT), d-lactate dehydrogenase (D-LDH), β-ketothiolase (PhaA), and NADPH-dependent acetoacetyl-CoA reductase (PhaB)], MCL-3HA monomers supplying enzymes [(R)-3-hydroxyacyl-ACP thioesterase (PhaG) and (R)-3-hydroxyacyl (3HA)-CoA ligase] via fatty acid biosynthesis pathway, and modified polyhydroxyalkanoate (PHA) synthase [PhaC1(STQK)] of Pseudomonas sp. 61-3 were introduced into E. coli LS5218. This resulted in the synthesis of a novel LA-based copolymer, P(LA-co-3HB-co-3HA). ¹H-nuclear magnetic resonance (NMR) analysis revealed the composition of P(LA-co-3HB-co-3HA) to be 19.7 mol% LA (C₃), 74.9 mol% 3HB (C₄), and 5.4 mol% MCL-3HA units of C₈ and C₁₀. Furthermore, the recombinant E. coli CAG18497 strain carrying these genes, excluding the phaAB genes, accumulated P(92.0% LA-co-3HA) with a novel monomer composition containing C₃, C₈, C₁₀, and C₁₂. ¹³C-NMR analysis showed the existence of LA-3HA sequence in the polymer. The solvent cast film of P(92.0% LA-co-3HA) exhibited transparency similar to poly(lactic acid).

Keywords: Biodegradable plastic; Biopolymer; Poly(lactic acid); Polyhydroxyalkanoate; d-Lactate dehydrogenase.