Pretreatment products from lignocellulose could provide abundant feedstocks for industrial biofuel production from fermentation. Xylose and glucose are the major products from pretreatment. However, the fermentation efficiency is relatively low because of the complex composition and the presence of inhibitors in the pretreatment products.
Extracellular electron shuttles are a group of compounds that can cycle between oxidized and reduced forms and facilitate electron transfer. Based on our previous study, the reduced form of extracellular electron shuttles, such as AH2QDS, can dramatically increase biohydrogen production by Clostridium fermentation. Geobacter can regenerate AH2QDS using fermentation products such as acetate and butyrate. In co-culture fermentation, Geobacter is expected to use fermentation products from Clostridium to regenerate AH2QDS, which in turn could enhance the biohydrogen production by Clostridium.
We’ve demonstrated improved substrate utilization and hydrogen production by co-culture fermentation compared to Clostridium alone when using xylose as model substrate. The fermentation products decreased, consistent with Geobacter utilizing them to regenerate the reduced form of the extracellular electron shuttles. Molecular microbiology data further supported this conclusion. Co-culture fermentation was also applied to the complex substrate such as the products from thermochemical conversion of Miscanthus, which mainly consists of xylose, glucose and inhibitors. Better utilization of those pretreatment products and biohydrogen production were achieved in co-culture.