Synthesis of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) with a target mole fraction of 4-hydroxybutyric acid units by two-stage continuous cultivation of Delftia acidovorans P4a

Abstract

Delftia acidovorans P4a (DSMZ 10474) was grown in mineral medium on acetic acid at pH 8.0 without an additional supply of nutrients like yeast extract or polypeptone. Using acetic acid and γ-butyrolactone (GBL), copolymers with a 4HB content from 2-90 mol % were detected in batch experiments, depending on the ratio of the both carbon substrates. Due to the different consumption rates of the individual carbon substrates a multitude of different target mole fractions were difficult to produce by fed-batch fermentation. Therefore, the two-stage continuous cultivation technique was applied with two fermenters connected in series. At stage 2, the optimum PHA productivity of the bioreactor and a target 4HB content of the polymer could be precisely adjusted by the composition of the two substrates. This cultivation strategy was especially convenient when toxic substrates like acetic acid and GBL were employed. Using mixtures of acetic acid and GBL (3.5-23.5 mol % GBL), copolymers with a target mole fraction of 2.7-19 % 4HB could be produced. The PHA content was in the range of 52-60 %. The dilution rates (D) of the first and second fermenter were 0.2 h-1 and 0.06 h-1, respectively. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.