Kinetic analysis on formation of poly(3-hydroxybutyrate) from acetic acid by Ralstonia eutropha under chemically defined conditions

Batch cultures of Ralstonia eutropha in chemically defined media with aceti c acid (HAc) as the sole carbon source were conducted to investigate acetat e utilization, formation of poly(3-hydroxybutyrate) (PHB) and growth of act ive biomass (ABM) under different carbon to nitrogen (CIN) weight ratios. T he specific acetate utilization rate based on ABM approached 0.16 g/g ABM h (-1), which was not affected very much by the extracellular HAc concentrati on from 1 to 5 g/l, but was affected by the CIN weight ratio. A low C/N rat io or high nitrogen supply sped up the specific acetate utilization rate to produce more ABM and less PHB. A high HAc concentration (>6 g/l), however, depressed acetate utilization as well as the ABM growth and PHB formation. A high cell mass concentration enhanced the tolerance of R, eutropha to th e toxicity of HAc at pH 7 to 8.5. The viscosity-average molecular size of P HB generally increased first and then declined in batch cultures. Larger PH B molecules and less PHB per ABM were produced at a low CIN ratio with enou gh nutrient nitrogen than those under a high C/N ratio with less nutrient n itrogen available.