Production of heteropolymeric polyhydroxyalkanoate in Eschericha coli from a single carbon source

• Published in: International journal of biological macromolecules 1996, Vol.19 (2), p.121-130
• Main Authors: Eschenlauer, Arthur C., Stoup, Sandra K., Srienc, Friedrich, Somers, David A.
• Format: Article
• Language: English
• Subjects: Poly-β-hydroxyalkanoic acids; Poly[β-hydroxybutyrate-co-β-hydroxyvalerate] co-polymer; Propionyl co-enzyme A; Pyruvate dehydrogenase; Threonine dehydratase; α-Ketobutyrate
• ISSN: 0141-8130; 1879-0003
• DOI: 10.1016/0141-8130(96)01114-2

Poly[β-hydroxybutyrate-co-β-hydroxyvalerate]co-polymer, PHBV, is a polyhydroxyalkanoate (PHA) that has greater utility as a biodegradable thermoplastic polyester than poly-β-hydroxybutyrate, PHB. In order to produce PHBV, a system of pathways is required to produce both hydroxybutyrate (HB) and hydroxyvalerate (HV) monomers from the sources of carbon. A working model for conversion of glucose to PHBV via acetyl- and propionyl-coenzyme A was constructed by expressing the PHA biosynthesis genes from Alcaligenes eutrophus in Escherichia coli strain K-12 under novel growth conditions. When 1 mM valine was added to 1% glucose medium, growth ceased and up to 2.5% of the incorporated monomers were HV; up to 4% were HV when 1 mM threonine was added as well. Threonine dehydratase (TD) converts threonine to α-ketobutyrate; TD is required for HV to be incorporated into PHA unless its transaminated reaction product, α-aminobutyrate, is added to the medium. Intracellular α-ketobutyrate accumulates when valine is added to the medium because valine, which cannot be metabolized to HV by E. coli strain K-12, stimulates TD and inhibits acetolactate synthase. In turn, α-ketobutyrate is converted to propionyl-CoA by the E. coli pyruvate dehydrogenase complex. This constitutes a defined system of pathways for synthesis of a heteropolymeric PHA from a single carbon source, which in the future could be transferred to other organisms including plants