Continuous production of poly-3-hydroxybutyrate by Ralstonia eutropha in a two-stage culture system

Abstract

Poly-3-hydroxybutyrate (PHB) is mainly accumulated by Ralstonia eutropha under unbalanced growth conditions, which limits its production in batch or fed-batch modes. The continuous production of PHB was investigated in a two-stage continuous culture system. The first-stage produced cell mass giving the maximal cell dry weight of 27.1 g l −1 at 0.21 h −1 of dilution rate. High specific cell growth rate results in the decrease of PHB synthesis under glucose-limited and nitrogen-rich conditions in the first-stage. The second-stage produced PHB giving the maximal PHB concentration of 47.6 g l −1 at 0.14 h −1 of dilution rate. Specific PHB synthetic rate reached highest value at low dilution rate under nitrogen-limited condition in the second-stage, and decreased with the increase of ammonium concentration in the culture. In the continuous culture system, the maximal PHB productivity could reach 1.43 g l −1 h −1 at a dilution rate of 0.12 h −1, but with relatively low PHB content of 47.6%. Maximal yield of PHB on glucose could reach 0.36 g g −1 glucose at 0.075 h −1 of dilution rate with relatively high PHB productivity of 1.23 g l −1 h −1 and PHB content of 72.1%, respectively.