Polyhydroxybutyrate/valerate production from methanol by Methylorubrum extorquens : Process limiting factors and polymer characterisation

This study investigates production of poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate- co -3-hydrox- yvalerate) (PHBV) by Methylorubrum extorquens from methanol and pentanol in automated fed -batch cultures. An in -line methanol sensor was implemented to control methanol addition. A cell growth phase (solely using methanol as carbon source) was always followed by a PHB(V) production phase induced by nitrogen limitation. The highest biomass productivity and yield in the cell growth phase were 0.82 g.L -1 .h -1 and 0.34 g.g - 1 , respectively. Different ratios of pentanol to methanol (from 0 % to 20 vol%) were applied in the PHB(V) production phases. The presence of pentanol significantly decreased the glass transition and melting temperature of the polymers and the ratio of pentanol to methanol in the feed had a significant effect on the PHV yield (ratio of the produced PHV polymer to the consumed pentanol). The highest PHV yield (63 %) was obtained at 2 vol% pentanol.