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

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). 1 H-nuclear magnetic resonance (NMR) analysis revealed the composition of P(LA- co -3HB- co -3HA) to be 19.7 mol% LA (C 3 ), 74.9 mol% 3HB (C 4 ), and 5.4 mol% MCL-3HA units of C 8 and C 10 . 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 C 3 , C 8 , C 10 , and C 12 . 13 C-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).