Bottlenecks in lignocellulosic ethanol production: xylose fermentation and cell propagation.

Researchers: Marlous van Dijk, Mats Galbe and Ola Wallberg (Lund University), Rakesh Koppram (Taurus Energy AB), Lisbeth Olsson

Lignocellulose derived bio-ethanol will play a key role in providing the transportation sector with fossil free fuels. However, two major remaining challenges for the development of feasible process economics is low xylose productivity and low inhibitor tolerance of the utilized Saccharomyces cerevisiae strains. Lignocellulosic inhibitors, have been shown to affect xylose conversion far more than glucose likely because xylose produces less cellular energy which is necessary to drive the cellular coping mechanisms against toxicity.

Within this project we try to tackle both of the major challenges in one approach: through adaptation during propagation. The propagation consists of a serial transfer of cultures to new (and larger volumes of) medium until the desired concentration of cells is reached. In order to achieve industrially relevant fermentation times, a high concentration of yeast cells (±4 gCDW L-1) is required for inoculation of lignocellulose ethanol fermentations. Previous work within the Industrial Biotechnology division has shown that yeast cells that are adapted to hydrolysate during propagation, not only show improved inhibitor tolerance but also improved xylose consumption rates. Currently, we focus on getting a better understanding of the physiological mechanisms that underlie these observations. Ultimately, we want to be able to explain how yeast cultures produced by an optimized propagation strategy differ from non-adapted cultures and which cellular mechanisms are responsible for these differences. We will desing highly flexible model propagation procedure to accommodate both researchers and industrial operators in guiding their respective work to a deeper understanding and more robust fermentations.

This research is funded by the Swedish Energy Agency.

Published: Thu 08 Dec 2016.