Technical assessment of cellulosic ethanol production using ß-glucosidase producing yeast Clavispora NRRL Y-50464

Authors: Liu, Zonglin; Cotta, Michael

Submitted to: BioEnergy Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/24/2015
Publication Date: 1/16/2015
Publication URL: http://link.springer.com/article/10.1007/s12155-014-9575-9/fulltext.html
Citation: Liu, Z., Cotta, M.A. 2015. Technical assessment of cellulosic ethanol production using ß-glucosidase producing yeast Clavispora NRRL Y-50464. BioEnergy Research. DOI: 10.1007/s12155-014-9575-9.

Interpretive Summary: Conventional cellulosic ethanol conversion from lignocellulosic materials by simultaneous saccharification and fermentation (SSF) requires addition of the enzymes, cellulase and ß-glucosidase. Currently, the supplementary ß-glucosidase enzyme is considered a major expense, which represents a significant challenge for a low-cost advanced biofuels production. In addition, ethanol titer and conversion rate of currently available strains are too low for sustainable industrial application. In this research, ARS scientists demonstrated a novel ethanologenic yeast strain that is able to convert cellulosic materials to ethanol in high yield without the addition of supplementary ß-glucosidase by SSF. This strain produced 40.44 g/L cellulosic ethanol from pure cellulose within 72 h with a conversion rate of 0.04g/L/h. From delignified corn stover cellulose it produced 28.2g/L ethanol at a rate of 0.041 g/L/h, which is significantly higher than that from conventional pretreated corn stover. In 2-liter bioreactor SSF, this strain produced 32 g/L ethanol from conventional corn stover cellulose within 48 h with a conversion rate of 0.088 g/L/h. All of these ethanol titers and conversion rates are the highest values for cellulosic ethanol conversion reported in the literature. Collectively, the rapid production of ethanol in high yield and robust nature of this strain make it an attractive candidate biocatalyst for lower-cost advanced biofuels production from lignocellulosic materials.

Technical Abstract: Reducing the cost of cellulosic ethanol production, especially the use of expensive exogenous cellulose hydrolytic enzymes such as cellulase and ß-glucosidase, is a critical challenge and vital for a sustainable advanced biofuels industry. Here we report a novel ethanologenic yeast strain Clavispora NRRL Y-50464 that produces sufficient innate ß-glucosidase enzyme activity for cellulosic ethanol production by simultaneous saccharification and fermentation (SSF). In a bottle SSF, strain Y-50464 produced 40.44 g/L ethanol from pure cellulose within 72 h at a conversion rate of 0.04 g/L/h applying conventional cellulase without supplementary ß-glucosidase. Ethanol conversion from delignified corn stover by Y-50464 showed significantly higher titers and rates at various solids loading levels than that from conventional pretreated corn stover with over 40 to 60% improved efficiency in a bottle SSF. However, the bottle SSF was inefficient for mixing higher levels of cellulose feedstock and should be replaced by a more suitable experimental apparatus. In a 2-L bioreactor SSF using conventional dilute acid pretreated corn stover, strain Y-50464 produced 32 g/L ethanol from 20% solids loading at 48 h applying cellulase alone without addition of ß-glucosidase. This represented a conversion rate of 0.088 g/L/h, the highest rate so far for cellulosic ethanol production from lignocellulosic materials. Elimination of ß-glucosidase in cellulose-to-ethanol fermentation would be expected to reduce cost of cellulose conversion. The robustness, fast growth rate, and the capability of producing both ethanol and ß-glucosidase illustrated the potential of strain Y-50464 as a potential candidate biocatalyst for advanced biofuels production from lignocellulosic biomass.