Location: Bioenergy Research Unit
Title: Comparisons of five Saccharomyces cerevisiae strains for ethanol production from SPORL pretreated lodgepole pine Authors
Submitted to: Biotechnology Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 10, 2014
Publication Date: N/A
Interpretive Summary: Fermentation of woody biomass into ethanol is challenging because the extracted sugars are a mixture and inhibitory chemicals are released during the extraction process. In particular, the sugar mixture contains xylose and this sugar is not fermented by brewer’s yeasts. We have developed a set of yeast strains engineered to ferment xylose that are expected to be robust to adverse culture conditions because their parents are industrial yeasts. We have evaluated two of these engineered yeast strains and their respective parents on a sugar mixture prepared from Lodgepole pine. The engineered strain YRH400 and its parent D5A fermented the glucose and galactose present, thereby, successfully overcoming the inhibitory environment. Unfortunately, YRH400 did not ferment the xylose, which we attribute to the low concentration of xylose present. This work shows that the use of industrial yeast backgrounds is desirable for overcoming the effects of inhibitors and that further engineering is required to enable fermentation of xylose at low concentrations. This paper will be of interest to those working in the wood processing industry and microbiologists developing new biocatalysts for ethanol production.
Technical Abstract: The performances of 5 yeast strains under three levels of toxicity were evaluated using hydrolysates from lodgepole pine pretreated by Sulfite Pretreatment to Overcome the Recalcitrance of Lignocelluloses (SPORL). The highest level of toxicity was represented by the whole pretreated biomass slurry, while intermediate toxicity was represented by the hydrolysate with partial loading of pretreatment spent liquor. The zero toxicity was represented using the enzymatic hydrolysate made from thoroughly washed SPORL lodgepole pine solids. The results indicate that strains D5A and YRH400 can tolerate the whole pretreated biomass slurry to produce 90.1 and 73.5% theoretical ethanol yield, respectively, at a relatively low yeast loading of optical density of 3.5. Strains Y1528, YRH403, and FPL450 were only able to ferment the hydrolysate with intermediate toxicity with lower ethanol productivity than D5A and YRH400. Both YRH400 and YRH403 were genetically engineered for xylose fermentation but were not able to consume xylose efficiently.