Development of commercial yeast strains for efficient conversion of lignocellulosic biomass into ethanol

Toyota has been developing the robust ethanol fermenting yeasts that have sufficient tolerance to the hydrolysate inhibitors and efficient conversion of pretreated biomass into ethanol by genetic modification and evolutionary engineering for cost-efficient production of lignocellulosic ethanol. In addition to tuning gene expression of the original xylose isomerase and the pentose phosphate pathway, the acetate metabolic pathway 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 significantly higher xylose consumption, enhanced ethanol yield, enabling fermentation at comparatively high temperature and cell recycling, as well as high resistance against the inhibitors in dilute acid pretreated biomass.

In addition, 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. Developed strains have achieved high ethanol concentrations and ethanol yields, well above 90%, under SHF conditions, in lignocellulosic substrates over 15% total solids, with complete conversion of xylose and glucose within 48 hours. The latest scientific results will be presented as well as an update on the strain’s development towards commercial production.