Development of yeast strain for enhanced tolerance to hydrolysates toward commercial production of cellulosic ethanol

For cost-efficient production of lignocellulosic ethanol, Toyota has developed a robust ethanol fermenting yeast that have sufficient tolerance to the inhibitors in pretreated biomass, such as acetic acid and furfural, by genetic modification and evolutionary engineering. In addition to up-regulation of the efficient xylose isomerase and the pentose phosphate pathway, the cellular redox balance was modified. All inserted genes are stably integrated in the genome of the yeast and the strains have subjected to extensive evolutionary engineering, resulting in very improved xylose consumption, low formation of xylitol, enabling fermentation at comparatively high temperature and cell recycling, as well as high resistance against the inhibitors in dilute acid pretreated biomass.

In addition, the processing conditions for the dilute acid pretreatment of biomass have been optimized and various saccharification and fermentation strategies have been developed to optimize the performance of the strain. By adjusting condition of enzymatic liquefaction and fed-batch fermentations, optimizing e.g. sugar concentrations and growth conditions, improved yields and productivities can be achieved even at low enzyme loading.

Toyota’s strains have achieved high ethanol concentrations and ethanol yields, well above 90%, under SHF conditions, in lignocellulosic substrates, with complete conversion of xylose and glucose in a short period of time. The latest scientific results will be presented as well as an update on the strain’s development towards commercial production.