Consolidated bioprocessing of untreated switchgrass to hydrogen by the extreme thermophile Caldicellulosiruptor saccharolyticus DSM 8903

The abilities of the extreme thermophilic bacterium Caldicellulosiruptor saccharolyticus DSM 8903 to ferment switchgrass (SWG), microcrystalline cellulose (MCC) and glucose to hydrogen (H2) in one-step were examined. Hydrogen production from glucose reached the theoretical maximum for dark fermentation of 4 mol H2/mol glucose. The H2 yield on MCC and SWG after 6 days of fermentation was 23.2 mmol H2/L or 9.4 mmol H2/g MCC and 14.3 mmol H2/L or 11.2 mmol H2/g SWG, respectively. The rate of H2 formation however was higher on MCC (0.7 mmol/L h) than SWG (0.1 mmol/L h). C. saccharolyticus DSM 8903 was able to produce H2 directly from mechanically-comminuted SWG without any physicochemical or biological pretreatment. Combining four processing steps (pretreatment, enzyme production, saccharification and fermentation) into a single biorefinery operation makes C. saccharolyticus DSM 8903 a promising candidate for consolidated bioprocessing (CBP) of lignocellulosic biomass.