Microbial Production of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) in Escherichia coli By a Rational Metabolic Engineering

Polyhydroxyalkanoates(PHAs) are bacterial polyesters accumulated in many bacteria. Bio-based PHAs production has great interest because of their unique characteristics, biodegradable and biocompatible thermoplastic. Among lots of PHA copolymers, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] is one of the important copolymers because of lower melting point and much better flexible compared to current used in many application. So far, for the production of P(3HB-co-3HV), adding of second auxiliary carbon source was needed. However, due to the toxicity of auxiliary carbon source, it is very hard to maintain the balance between cell growth and P(3HB-co-3HV) production. Thus, we developed the E. coli can stably synthesize 3HB-CoA and 3HV-CoA in controlled ratio from glucose without feeding of exogenous auxiliary carbon source by metabolic engineering. Two different metabolic pathways for the production of propionyl-CoA from 2-ketobutyrate were constructed. The first one is composed of Dickeya dadantii 3937 2-ketobutyrate oxidase (2KO) or E. coli pyruvate oxidase mutant (PoxB V380A L253F) for the conversion of 2-ketobutyrate into propionate and Ralstonia eutropha propionyl-CoA synthetase (PrpE) for further activation of propionate into propionyl-CoA. Second one is consisted of E. coli 2-ketobutyate synthases (TdcE) or Clostridium difficile (PflB) for direct conversion of 2-ketobutyrate into propionyl-CoA. This engineered strain can efficiently synthesize P(3HB-co-3HV) independent with exogenous auxiliary carbon source. [This work was supported by the Technology Development Program to Solve Climate Changes on Systems Metabolic Engineering for Biorefineries from the Ministry of Science, ICT and Future Planning (MSIP) through the National Research Foundation (NRF) of Korea (NRF-2012M1A2A2026556 and NRF-2012M1A2A2026557).]