Evaluation of feeding regimes to enhance PHA production using acetic and butyric acids by a pure culture of Cupriavidus necator

In this study volatile fatty acids (VFAs), which are by-products from anaerobic fermentations, have been used as the carbon source for polyhydroxyalkanoates (PHA) production by pure culture bacteria, Cupriavidus necator. A number of factors influence the conversion efficiencies of VFAs to PHAs including the bacterial feeding regimes. When VFA was supplied as a single feed, it was found that concentrations higher than 2% v/v VFA led to substrate inhibition and only 18% acetic acid and 12% of butyric acid was converted into PHA. This resulted in less than 65% (w/w) of PHA content within the microbial cells. Hence, the single VFA feeding strategy was found to provide low conversion rates of VFA into polymer. An improved feeding strategy was found to be the use of an automatic VFA feed based on the pH control of the medium, which led to a more continuous feeding regime. The conversion of VFA to PHA was increased by almost 2-fold to 33 and 22% for acetic acid and butyric acid respectively, with up to 75% (w/w) of PHA resultant within the microbial cells.