Bioconversion of acid-hydrolyzed poplar hemicellulose to acetic acid byClostridium thermoaceticum

Clostridium thermoaceticum was used to ferment carbohydrate released from pretreated oat splet xylan and hemicellulose isolated from hybrid poplar. Hydrolysis with dilute sulfuric acid (2.5% (v/v) for oat spelt xylan and 4.0% (v/v) for poplar hemicellulose) at 100°C for 60 min was found to release the highest concentration of fermentable substrate.C. thermoaceticum, when grown in non-pH controlled batch culture at 55°C under a headspace of 100% CO2, typically produced 14gl−1 acetic acid during a 48 h fermentation in medium containing 2% xylose. In fed-batch fermentations this organism was able to produce 42gl−1 acetic acid after 116h when the concentration of xylose was maintained at approximately 2% and the pH was controlled at 7.0.