Fermentation of xylose into acetic acid by Clostridium thermoaceticum

For optimum fermentation, fermenting xylose into acetic acid by Clostridium thermoaceticum (ATCC 49707) requires adaptation of the strain to xylose me dium. Exposed to a mixture of glucose and xylose, it perferentially consume s xylose over glucose. The initial concentration of xylose in the medium af fects the final concentration and the yield of acetic acid. Batch fermentat ion 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 consume s fructose, xylose, and glucose from a mixture of sugars in batch fermentat ion. Arabinose, mannose, and galactose are consumed only slightly. This org anism loses viability on fed-batch operation, even with supplementation of all the required nutrients. In fed-batch fermentation with CSL supplementat ion, D-xylulose (an intermediate in the xylose metabolic pathway) accumulat es in large quantities.