A newly engineered strain of yeast that can simultaneously consume two types of sugar from plants to produce ethanol eliminates major inefficiencies associated with current biofuel production methods.
The sugars are glucose — a six-carbon sugar that is relatively easy to ferment, and xylose — a five-carbon sugar that has been much more difficult to use in ethanol production.
The work to develop the yeast strain was a collaborative effort led by researchers at the University of Illinois, the Lawrence Berkeley National Laboratory, the University of California and energy giant BP.
Yeasts feed on sugar and produce various waste products, some of which are useful to humans. One type of yeast, Saccharomyces cerevisiae, has been used for centuries in baking and brewing because it efficiently ferments sugars and in the process produces ethanol and CO2. The biofuel industry also uses the yeast to convert plant sugars to bioethanol.
But while Saccharomyces cerevisiae is good at feeding on glucose — a building block of cellulose and the primary sugar in plants — it cannot use xylose, a secondary — but significant — component of the lignocellulose that makes up plant stems and leaves. Most yeast strains that are engineered to metabolise xylose do so very slowly.
So Prof Yong-Su Jin from the University of Illinois and his colleagues developed the new yeast to quickly and efficiently consume both types of sugar at once, a process called co-fermentation.
In a painstaking process of adjustments to the original yeast, Jin and his team converted it to one that would consume both types of sugar faster and more efficiently than any strain currently in use in the biofuel industry. In fact, the new yeast strain simultaneously converts cellobiose (a precursor of glucose) and xylose to ethanol just as quickly as it can ferment either sugar alone.
The new yeast strain is claimed to be at least 20 per cent more efficient at converting xylose to ethanol than other strains, making it ’the best xylose-fermenting strain’ reported in any study.
Jin said: ’The cost benefits of this advance in co-fermentation are significant. We don’t have to do two separate fermentations. We can do it all in one pot. And the yield is even higher than the industry standard. We are pretty sure that this research can be commercialised very soon.’