Continuous production of poly-β-hydroxybutyrate by high-cell-density cultivation of Wautersia eutropha

BACKGROUND: Poly-beta-hydroxybutyrate (PHB) accumulation is triggered by limitation of a nutrient other than carbon. The production cost of PHB is very high. In order to reduce this cost, continuous cultivation for the accumulation of PHB was investigated. The culture was first allowed to grow under fed-batch conditions to yield a significant increase in biomass and PHB accumulation. Thereafter this high-cell-density biomass containing PHB was allowed to grow and maintained under conditions of continuous cultivation so that the overall process could be simplified and economised. RESULTS: For continuous cultivation a medium containing 90 g L-1 fructose and 2.5 g L-1 nitrogen (as urea) was fed continuously at a dilution rate of 0.1 h(-1). A steady state biomass of 27.7 g L-1 with a PHB concentration of 5.5 g L-1 was established in the bioreactor. This resulted in a continuous PHB productivity of 0.55 g L-1 h(-1). CONCLUSION: The experiments have resulted in the development of a novel production technology involving the integration of batch, fed-batch and continuous processes. At the same time the production of PHB under continuous cultivation increases the overall industrial importance of the system. (c) 2008 Society of Chemical Industry.