8-03: Yeast strain and fermentation development for commercial production of cellulosic ethanol

For commercial production of lignocellulosic ethanol, Terranol has developed a robust and rapid xylose fermenting yeast (Saccharomyces cerevisiae) by identifying and alleviating a previously unexplored bottleneck in the xylose metabolic pathway. In addition to up-regulation of the pentose phosphate pathway, and an efficient bacterial xylose isomerase, the strain expresses a xylose 1-epimerase. The epimerase catalyzes an otherwise slow conversion between the β- and α-epimers of D-xylose, of which only the α-epimer is a substrate of the xylose isomerase. All inserted genes are stably integrated in the genome of the yeast and the strain has undergone extensive evolutionary engineering, resulting in rapid xylose consumption, very low formation of xylitol, as well as high resistance towards biomass derived inhibitors.

In addition, various fermentation strategies have been developed to assess and optimize the performance of the strain. By moving from batch to controlled fed-batch fermentations, optimizing e.g. sugar concentrations and growth conditions, improved yields and productivities can be achieved. Results from these feed strategies can be used as input for large scale processes.

Terranol’s strain has achieved high ethanol concentrations and ethanol yields, well above 90%, in various lignocellulosic substrates, with complete conversion of xylose and glucose in a short period of time. The performance has been shown in lab and pilot scale fermentations, both in-house as well as at different partners. The latest scientific results will be presented as well as an update on the strain’s advancement towards commercial scale.