Fermentation of Xylose into Acetic Acid by Clostridium thermoaceticum

Abstract

For optimum fermentation, fermenting xylose into acetic acid by Clostridium thermoaceticum (ATCC 49707) requires adaptation of the strain to xylose medium. Exposed to a mixture of glucose and xylose, it preferentially consumes xylose over glucose. The initial concentration of xylose in the medium affects the final concentration and the yield of acetic acid. Batch fermentation of 20 g/L of xylose with 5 g/L of yeast extract as the nitrogen source results in a maximum acetate concentration of 15.2 g/L and yield of 0.76 g of acid/g of xylose. Corn steep liquor (CLS) is a good substitute for yeast extract and results in similar fermentation profiles. The organism consumes fructose, xylose, and glucose from a mixture of sugars in batch fermentation. Arabinose, mannose, and galactose are consumed only slightly. This organism loses viability on fed-batch operation, even with supplementation of all the required nutrients. In fed-batch fermentation with CSL supplementation, D-xylulose (an intermediate in the xylose metabolic pathway) accumulates in large quantities.