초록
<P><B>Tricks for boosting yeast's ethanol yields</B></P><P>To become a widely used source of fuel, widespread industrial production of ethanol using yeast needs to be simple and efficient. However, two conditions ideal for boosting production—tolerance of higher temperatures and high concentrations of ethanol—have been limiting (see the Perspective by Cheng and Kao). Now, Caspeta <I>et al.</I> have used adaptive laboratory evolution to find yeast strains that can tolerate high temperatures and Lam <I>et al.</I> have identified a route to improve yeast's resistance to high concentrations of ethanol.</P><P><I>Science</I>, this issue p. 75, p. 71; see also p. 35</P><P>Ethanol toxicity in the yeast <I>Saccharomyces cerevisiae</I> limits titer and productivity in the 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 multiple alcohols. The elevation of extracellular potassium and pH physically bolsters these gradients, increasing tolerance to higher alcohols and ethanol fermentation in commercial and laboratory strains (including a xylose-fermenting strain) under industrial-like conditions. Production per cell remains largely unchanged, with improvements deriving from heightened population viability. Likewise, up-regulation of the potassium and proton pumps in the laboratory strain enhances performance to levels exceeding those of 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.</P>