Biosynthesis and properties of poly(3-hydroxybutyrate-co-3-hydroxyalkanoates) by recombinant strains of Pseudomonas sp. 61-3.

Pseudomonas sp. 61-3 (phbC::tet) strain, which is a phbCPs-disrupted mutant, accumulated a random copolymer consisting of (R)-3-hydroxybutyrate (3HB) and (R)-medium-chain-length 3-hydroxyalkanoate (3HA) units of 6-12 carbon atoms, but the 3HB fraction in the copolymer was less than 50 mol %, resulting in the formation of an amorphus polymer. Therefore, the genes encoding beta-ketothiolase (PhbARe) and NADPH-dependent acetoacetyl-CoA reductase (PhbBRe) from Ralstonia eutropha were expressed under the control of promoters for Pseudomonas sp. 61-3 pha locus or R. eutropha phb operon together with the phaC1Ps gene (PHA synthase 1 gene) from Pseudomonas sp. 61-3 in the phbCPs-disrupted mutant. The recombinant strains synthesized P(3HB-co-3HA) copolymers with very high 3HB compositions (up to 94 mol %) from glucose. The number-average molecular weights of P(3HB-co-3HA) were in the range of 349 x 10(3) to 605 x 10(3). The structure and physical properties of P(3HB-co-3HA) copolymers were characterized by 1H- and 13C-NMR spectrometry, differential scanning calorimetry, and mechanical tensile measurement. P(94% 3HB-co-3HA) copolymer was demonstrated to have good physical properties and to be a flexible material with moderate toughness, similar to low-density polyethylene.