Increased poly(3-hydroxybutyrate) accumulation in recombinant Escherichia coli from whey by agitation speed control

Abstract

The timing of poly(3-hydroxybutyrate) (PHB) biosynthesis was controlled by varying the agitation speed of a stirred tank fermenter during the pH-stat fed-batch culture of recombinant Escherichia coli strain GCSC 6576 harboring pSYL107. Using a concentrated whey solution containing ca. 200 g/l lactose as the nutrient feed, the PHB content was only 57% after 35 h due to volumetric limitation of the fermenter. However, by limiting the oxygen by maintaining the agitation speed at 300 rpm, the final PHB content increased to 70% after 70 h with a cell concentration of 15 g/l. When the agitation speed was increased up to 500 rpm, a cell concentration of 31 g/l with 80% PHB was obtained after 52 h. A further increase in the maximum agitation speed increased the cell concentration, PHB concentration, and PHB productivity, however, the PHB content decreased to 56-58%.