Improved production of poly(3-hydroxybutyrate-co-4-hydroxbutyrate) copolymer using a combination of 1,4-butanediol and γ-butyrolactone

A locally isolated Gram-negative bacterium, Cupriavidus sp. USMAA2-4 was able to synthesize poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)] when fed with the precursor carbon 1,4-butanediol using a two-stage cultivation process. When 1% (w/v) of 1,4-butanediol was used, 31 wt.% of P(3HB-co-4HB) copolymer with 41 mol.% of 4HB molar fraction was produced. Both the PHA content and 4HB composition of the copolymer increased as the concentration of 1,4-butanediol increased but the cell biomass did not show any significant changes. However, the 4HB fraction could be further increased using a combination of γ-butyrolactone and 1,4-butanediol. As high as 84 mol.% of 4HB composition was achieved with a combination of 0.35% (w/v) 1,4-butanediol and 1.4% (w/v) γ-butyrolactone. Nevertheless, it was found that Cupriavidus sp. USMAA2-4 cells were inhibited by high concentration of γ-butyrolactone. P(3HB-co-4HB) copolymer was also successfully synthesized using a simplified aerated tank.