S85: Extracellular Electron Shuttling Compounds Increase Biological Butanol and Hydrogen Production in the Fermentative Pure Culture Clostridium beijerinckii

This research focuses on using extracellular electron shuttles to alter the metabolic pathways in Clostridium beijerinckii strain 8052 fermentation to increase butanol or hydrogen yield with glucose and xylose as a primary substrate.  1-5mM  anthraquinone-2,6-disulfonate (AQDS), the oxidized form of the electron shuttle, were introduced into a batch culture of C. beijerinckii and increased butanol yield by 2.5 to 5 times relative to glucose alone.  An electron mass balance of the system indicated that butyric acid equivalents decreased as butanol equivalents increased.    Adding 20 mM Fe(III) (as ferrihydrite or ferric citrate), which also acts as an electron sink, increased butanol yield by 5 times relative to the glucose-only control. Adding both 1 mM AQDS and 20 mM Fe(III) increased the yield up to 5.5 times relative to the glucose-alone control, for a yield of 0.37 and final butanol concentration of 90 mM.  The increase with Fe(III) is due to the fact that when AQDS is reduced, the hydroquinone immediately transfers electrons to the Fe(III) thus recycling the AQDS so that it can be reduced again.  This was also demonstrated when operating a microbial fuel cell with C. beijerinckii in the anode, in batch mode.  Butanol concentrations in the fuel cell with quinone present reached 9.1 mM compared to 0.41 mM in the fuel operated without quinone.  The quinone was able to cycle electrons to the electrode (which were then transferred to the cathode operating under aerobic conditions) and “pull” more electrons from the fermentative pathway, which increased butanol yield.