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

Poly-3-hydroxybutyrate (PHB) is mainly accumulated by Ralstonia eutropha un der unbalanced growth conditions, which limits its production in batch or f ed-batch modes. The continuous production of PHB was investigated in a two- stage continuous culture system. The first-stage produced cell mas giving t he 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 und er glucose-limited and nitrogen-rich conditions in the first-stage. The sec ond-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 cul ture. 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 wit relative ly low PHB content of 47.6%. Maximal yield of PHB on glucose could reach 0. 36 g g(-1) glucose at 0.975 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. (C) 2001 Elsevier Science B.V. All rights reserved.