The abilities of the extreme thermophilic bacterium Caldicellulosiruptor saccharolyticus DSM 8903 to ferment switchgrass (SWG), microcrystalline cellulose (MCC) and glucose to hydrogen (H-2) in one-step were examined. Hydrogen production from glucose reached the theoretical maximum for dark fermentation of 4 mol H-2/mol glucose. The H-2 yield on MCC and SWG after 6 days of fermentation was 23.2 mmol H-2/L or 9.4 mmol H-2/g MCC and 14.3 mmol H-2/L or 11.2 mmol H-2/g SWG, respectively. The rate of H-2 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 H-2 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. (C) 2013 The Authors. Published by Elsevier Ltd. All rights reserved.