Engineering alcohol tolerance in yeast fermentations

Ethanol toxicity in yeast Saccharomyces cerevisiae limits titer and productivity in industrial production of transportation bioethanol.  We show that strengthening the opposing potassium and proton electrochemical membrane gradients is a mechanism that enhances general resistance to ethanol. The same mechanism and protection method is also applicable to higher alcohols.  Elevation of extracellular potassium and pH physically bolster these gradients, increasing tolerance to higher alcohols and ethanol fermentation in commercial and laboratory strains (including a xylose-fermenting strain) under industrial-like conditions.  A key finding is that specific productivity (production per viable cell) remains largely unchanged with improvements deriving from heightened population viability. As such, yeast cultures remain highly (and equally) productive for as long as they stay viable.  Likewise, up-regulation of the potassium and proton pumps in the laboratory strain enhances performance to levels exceeding industrial strains.  Although genetically complex, alcohol tolerance can thus be dominated by a single cellular process, one controlled by a major physicochemical component but amenable to biological augmentation.