Microbial synthesis of poly((R)-3-hydroxybutyrate-co-3-hydroxypropionate) from unrelated carbon sources by engineered Cupriavidus necator.

Cupriavidus necator was engineered aiming to synthesize poly[(R)-3-hydroxybutyrate-co-3-hydroxypropionate] copolyester, P(3HB-co-3HP), from structurally unrelated carbon sources without addition of any precursor compounds. We modified a metabolic pathway in C. necator for generation of 3-hydroxypropionyl-CoA (3HP-CoA) by introducing malonyl-CoA reductase and the 3HP-CoA synthetase domain of trifunctional propionyl-CoA synthase; both members of the 3-hydroxypropionate cycle, a novel CO(2)-fixation pathway in the green nonsulfur bacterium Chloroflexus aurantiacus . In this recombinant strain, 3HP-CoA was expected to be provided from acetyl-CoA via malonyl-CoA, and then copolymerized by the function of polyhydroxyalkanoate synthase along with (R)-3-hydroxybutyryl-CoA synthesized from two acetyl-CoA molecules. C. necator wild-type strains H16 and JMP134 harboring the two heterologous genes actually synthesized P(3HB-co-3HP) copolyester with 0.2-2.1 mol % of 3HP fraction from fructose or alkanoic acids of even carbon numbers. Enzyme assay suggested that lower activity of 3HP-CoA synthetase than that of malonyl-CoA reductase caused the limited incorporation of 3HP unit into the copolyesters synthesized by the recombinant strains. The present study demonstrates the potential of engineering metabolic pathways for production of copolyesters having favorable characteristics from inexpensive carbon resources.