title: Comparison of solid-state and submerged-state fermentation for the bioprocessing of switchgrass to ethanol and acetate by Clostridium phytofermentans.
abstract: The conversion of sustainable energy crops using microbiological fermentation to biofuels and bioproducts typically uses submerged-state processes. Alternatively, solid-state fermentation processes have several advantages when compared to the typical submerged-state processes. This study compares the use of solid-state versus submerged-state fermentation using the mesophilic anaerobic bacterium Clostridium phytofermentans in the conversion of switchgrass to the end products of ethanol, acetate, and hydrogen. A shift in the ratio of metabolic products towards more acetate and hydrogen production than ethanol production was observed when C. phytofermentans was grown under solid-state conditions as compared to submerged-state conditions. Results indicated that the end product concentrations (in millimolar) obtained using solid-state fermentation were higher than using submerged-state fermentation. In contrast, the total fermentation products (in weight of product per weight of carbohydrates consumed) and switchgrass conversion were higher for submerged-state fermentation. The conversion of xylan was greater than glucan conversion under both fermentation conditions. An initial pH of 7 and moisture content of 80 % resulted in maximum end products formation. Scanning electron microscopy study showed the presence of biofilm formed by C. phytofermentans growing on switchgrass under submerged-state fermentation whereas bacterial cells attached to surface and no apparent biofilm was observed when grown under solid-state fermentation. To our knowledge, this is the first study reporting consolidated bioprocessing of a lignocellulosic substrate by a mesophilic anaerobic bacterium under solid-state fermentation conditions.
authors.affiliation: Department of Biological Sciences, Clemson University, 132 Long Hall, Clemson, SC 29634, USA.
authors.forename: Abhiney
authors.initials: A
authors.lastname: Jain
authors.forename: Charles K
authors.initials: CK
authors.lastname: Morlok
authors.forename: J Michael
authors.initials: JM
authors.lastname: Henson
mesh_terms: D000085:Acetates / Q000378:metabolism*; D003013:Clostridium / Q000378:metabolism*; D000431:Ethanol / Q000378:metabolism*; D005285:Fermentation / Q000502:physiology; D008031:Lignin / Q000378:metabolism; D014990:Xylans / Q000378:metabolism
chemical_list: D000085:Acetates; D014990:Xylans; C036909:lignocellulose; D000431:Ethanol; D008031:Lignin