Trends in Brewing edition:11 location:Ghent date:13-17 April 2014
In addition to efficient pentose utilization, high inhibitor tolerance is a key feature required in any organism used for economically viable bioethanol production with lignocellulose biomass. Although recent work has succeeded in establishing xylose fermentation in Saccharomyces cerevisiae strains, little is known about the potential of yeast species other than S. cerevisiae for bioethanol production. The aim of this work was to evaluate the performance of other yeast species for the production of 2nd generation bioethanol.
2. Materials and Methods
We have screened a few hundred non S. cerevisiae yeast strains isolated from soil, plant nectar and sugar beet thick juice for various parameters, including xylose utilization, tolerance against fermentation inhibitors such as 5-hydroxymethylfurfural (HMF), high ethanol concentration, and osmotic stress. Subsequently, the eight best performing strains were subjected to bioethanol fermentation on an Eppendorf BioFlo310 bioreactor using (i) a high glucose concentration medium and (ii) a synthetic lignocellulotic hydrolysate medium containing HMF, furfural, acetic acid, formic acid, vannilinic acid and levulinic acid, and compared with the performance of the industrial S. cerevisiae strain Ethanol Red.
Wickerhamomyces anomalus and Pichia kudriavzevii were found as the most promising strains showing good ethanol tolerance, moderate inhibitor tolerance and xylose utilization. Other strains showed poor ethanol tolerance compared to Ethanol Red. In contrast, various Candida bombi and Starmerella bombicola strains as well as some W. anomalus and Metchnikowia pulcherrima strains showed better HMF tolerance compared to Ethanol Red. Fermentation experiments supported the potential of these yeasts for bioethanol production.
4. What’s innovative
Exploration of wild yeast species and genera for bioethanol production in comparison with currently used Saccharomyces cerevisiae strains.
5. Practical relevance
Future bioethanol fermentation processes need specific ethanol producing strains in order to increase the efficiency of fermentation (e.g. very high gravity fermentation) or to cope with stressors which are related to fermentation of lignocellulosic material hydrolysate. This might need a wider scope beyond the currently used Saccharomyces cerevisiae strains.