ARS | Publication request: A new beta-glucosidase producing yeast for lower-cost cellulosic ethanol production from xylose-extracted corncob residues by simultaneous saccharification and fermentation

Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 28, 2011
Publication Date: November 10, 2011
Citation: Liu, Z., Weber, S.A., Cotta, M.A., Li, S. 2012. A new beta-glucosidase producing yeast for lower-cost cellulosic ethanol production from xylose-extracted corncob residues by simultaneous saccharification and fermentation. Bioresource Technology. 104:410-416.

Interpretive Summary: Expenses for additional enzymes for cellulose deconstruction and degradation are one of the major costs of cellulosic ethanol production. Our research developed a new yeast strain able to produce a native ß-glucosidase that can ferment cellobiose to ethanol so no additional ß-glucosidase needs to be added in the fermentation process. This yeast is also tolerant to pretreatment inhibitors and higher temperatures allowing the enzymatic saccharification and microbial growth and fermentation can be carried out at the same temperature. Using an industrial byproduct xylose-extracted corncob residue as an example, this new yeast produced 23 g/L ethanol with a 25% solid load without addition of ß-glucosidase by simultaneous saccharification and fermentation (SSF) at 37 deg C. Development of this yeast simplifies fermentation procedures and facilitates economic consolidated SSF bio-processing. Output of this research aids efforts for lower-cost cellulosic ethanol production.

Technical Abstract: Conventional cellulose-to-ethanol conversion by simultaneous saccharification and fermentation (SSF)requires enzymatic saccharification using both cellulase and ß-glucosidase allowing cellulose utilization by common ethanologenic yeast. Here we report a new yeast strain of Clavispora NRRL Y-50464 that is able to utilize cellobiose as sole carbon source and produce sufficient native ß-glucosidase enzyme activity for cellulosic ethanol production using SSF. In addition, this yeast is tolerant to the major inhibitors derived from lignocellulosic biomass pre-treatment such as 2-furaldehyde (furfural) and 5-(hydroxymethyl)-2-furaldehyde (HMF), and converted furfural into furan methanol in less than 12 h and HMF into furan-2,5-dimethanol within 24 h in the presence of 15 mM each of furfural and HMF. Using xylose-extracted corncob residue as cellulosic feedstock, an ethanol yield of 23 g/L was obtained using 25% solids loading at 37 deg C by SSF without addition of exogenous ß-glucosidase. Development of this yeast aids renewable biofuels development efforts for economic consolidated SSF bio-processing.