Comparison of solid-state and submerged-state fermentation for the bioprocessing of switchgrass to ethanol and acetate by Clostridium phytofermentans

• Published in: Applied microbiology and biotechnology Vol. 97; no. 2; pp. 905 - 917
• Main Authors: Jain, Abhiney, Morlok, Charles K., Henson, J. Michael
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 2013; Springer Nature B.V
• Subjects: Acetates - metabolism; Biodiesel fuels; Bioenergy and Biofuels; Biofilms; Biofuels; Biological products; Biomass; Biomedical and Life Sciences; Biotechnology; Carbohydrates; Clostridium; Clostridium - metabolism; Crops; Energy; Energy crops; Enzymes; Ethanol; Ethanol - metabolism; Fermentation; Fermentation - physiology; Hydrogen production; Life Sciences; Lignin - metabolism; Lignocellulose; Microbial Genetics and Genomics; Microbiology; Microorganisms; Moisture content; Plastics; Raw materials; Studies; Sustainable energy; Xylans - metabolism; United States > US; Xylan; Solid-state fermentation; Ethanol; Lignocellulose
• ISSN: 0175-7598; 1432-0614
• DOI: 10.1007/s00253-012-4511-4

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.