title: Enhanced cofermentation of glucose and xylose by recombinant Saccharomyces yeast strains in batch and continuous operating modes.
abstract: Agricultural residues, such as grain by-products, are rich in the hydrolyzable carbohydrate polymers hemicellulose and cellulose; hence, they represent a readily available source of the fermentable sugars xylose and glucose. The biomass-to-ethanol technology is now a step closer to commercialization because a stable recombinant yeast strain has been developed that can efficiently ferment glucose and xylose simultaneously (coferment) to ethanol. This strain, LNH-ST, is a derivative of Saccharomyces yeast strain 1400 that carries the xylose-catabolism encoding genes of Pichia stipitis in its chromosome. Continuous pure sugar cofermentation studies with this organism resulted in promising steady-state ethanol yields (70.4% of theoretical based on available sugars) at a residence time of 48 h. Further studies with corn biomass pretreated at the pilot scale confirmed the performance characteristics of the organism in a simultaneous saccharification and cofermentation (SSCF) process: LNH-ST converted 78.4% of the available glucose and 56.1% of the available xylose within 4 d, despite the presence of high levels of metabolic inhibitors. These SSCF data were reproducible at the bench scale and verified in a 9000-L pilot scale bioreactor.
authors.affiliation: Biotechnology Center for Fuels and Chemicals, National Renewable Energy Laboratory (NREL), 1617 Cole Boulevard, Golden, CO 80401, USA.
authors.forename: S T
authors.initials: ST
authors.lastname: Toon
authors.forename: G P
authors.initials: GP
authors.lastname: Philippidis
authors.forename: N W
authors.initials: NW
authors.lastname: Ho
authors.forename: Z
authors.initials: Z
authors.lastname: Chen
authors.forename: A
authors.initials: A
authors.lastname: Brainard
authors.forename: R E
authors.initials: RE
authors.lastname: Lumpkin
authors.forename: C J
authors.initials: CJ
authors.lastname: Riley