Synthesis of polyhydroxyalkanoates from glucose that contain medium-chain-length monomers via the reversed fatty acid β-oxidation cycle in Escherichia coli.

Polyhydroxyalkanoates that contain the medium-chain-length monomers (mcl-PHAs) have a wide range of applications owing to their superior physical and mechanical properties. A challenge to synthesize such mcl-PHAs from unrelated and renewable sources is exploiting the efficient metabolic pathways that lead to the formation of precursor (R)-3-hydroxyacyl-CoA. Here， by engineering the reversed fatty acid β-oxidation cycle， we were able to synthesize mcl-PHAs in Escherichia coli directly from glucose. After deletion of the major thioesterases， the engineered E. coli produced 6.62wt% of cell dry weight mcl-PHA heteropolymers. Furthermore， when a low-substrate-specificity PHA synthase from Pseudomonas stutzeri 1317 was employed， recombinant E. coli synthesized 12.10wt% of cell dry weight scl-mcl PHA copolymers， of which 21.18mol% was 3-hydroxybutyrate and 78.82mol% was medium-chain-length monomers. The reversed fatty acid β-oxidation cycle offered an efficient metabolic pathway for mcl-PHA biosynthesis in E. coli and can be further optimized.