Production of heteropolymeric polyhydroxyalkanoate in Escherichia coli from a single carbon source.
Poly[beta-hydroxybutyrate-co-beta-hydroxyvalerate] co-polymer, PHBV, is a polyhydroxyalkanoate (PHA) that has greater utility as a biodegradable thermoplastic polyester than poly-beta-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 alpha-ketobutyrate; TD is required for HV to be incorporated into PHA unless its transaminated reaction product, alpha-aminobutyrate, is added to the medium. Intracellular alpha-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, alpha-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.
Eschenlauer
A C
AC
Department of Agronomy and Plant Genetics, University of Minnesota-St. Paul 55108-6026, USA.
Stoup
S K
SK
Srienc
F
F
Somers
D A
DA
D000214:Acyl Coenzyme A / Q000378:metabolism; D000421:Alcaligenes / Q000235:genetics / Q000378:metabolism; D002087:Butyrates / Q000378:metabolism; D002244:Carbon / Q000378:metabolism; D002455:Cell Division; D003470:Culture Media; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D006885:Hydroxybutyrates / Q000378:metabolism; D007532:Isoleucine / Q000096:biosynthesis; D010421:Pentanoic Acids / Q000378:metabolism; D010957:Plasmids / Q000235:genetics; D011091:Polyesters / Q000378:metabolism*; D011768:Pyruvate Dehydrogenase Complex / Q000378:metabolism; D013379:Substrate Specificity; D013912:Threonine / Q000378:metabolism; D013913:Threonine Dehydratase / Q000378:metabolism; D014169:Transformation, Bacterial; D014633:Valine / Q000378:metabolism; D000094122:Polyhydroxybutyrates
D000214:Acyl Coenzyme A; D002087:Butyrates; D002244:Carbon; D003470:Culture Media; D005947:Glucose; D006885:Hydroxybutyrates; D007532:Isoleucine; D010421:Pentanoic Acids; D011091:Polyesters; D011768:Pyruvate Dehydrogenase Complex; D013912:Threonine; D013913:Threonine Dehydratase; D014633:Valine; C052620:poly(3-hydroxybutyrate)-co-(3-hydroxyvalerate); D000094122:Polyhydroxybutyrates; C013056:beta-hydroxyvaleric acid; C003182:poly-beta-hydroxybutyrate; C009061:propionyl-coenzyme A; C005087:alpha-ketobutyric acid