Anthrahydroquinone-2,6,-disulfonate (AH sub(2)QDS) increases hydrogen molar yield and xylose utilization in growing cultures of Clostridium beijerinckii

H sub(2) production and xylose utilization were investigated using the fermentative culture Clostridium beijerinckii NCIMB 8052. Adding anthrahydroquinone-2,6-disulfonate (AH sub(2)QDS) increased the extent of xylose utilization by 56% and hydrogen molar yield by 24-37%. Enhanced hydrogen molar yield correlated with increased xylose utilization and increases in the acetate/butyrate product ratio. An electron balance indicated that AH sub(2)QDS shifted the electrons from the butyric acid pathway (NADH-dependent pathway) to the acetic acid pathway (non-NADH-dependent pathway), putatively creating a surplus of reducing equivalents that were then available for hydrogen production. These data demonstrate that hydrogen yield and xylose utilization can be manipulated by amending redox active molecules into growing cultures. This will impact biohydrogen/biofuel production by allowing physiological manipulations of growing cells for increased (or decreased) output of selected metabolites using amendments that are not consumed during the reactions. Although the current yield increases are small, they suggest a target for cellular alterations. In addition, increased xylose utilization will be critical to the fermentation of pretreated lignocellulosic feedstocks, which may have higher xylose content.