Fungal enzyme gives yeast green energy boost

Green fuels, like bioethanol, produced by yeast fermentation of plant sugars can be used to cut greenhouse gas emissions. Unfortunately, yeasts are naturally metabolically unequipped to make use of a major component of plant matter, the cellulose polymers that make up plant cell walls.

But now, with the help of some genetic know-how from a plant-degrading fungus, scientists have succeeded in producing modified yeasts capable of fermenting food that was formerly indigestible.

Writing in Science, UC Berkley researcher Jonathan Galazka and his colleagues borrowed a series of recently-identified genes found in a fungus called Neurospora crassa and inserted them into Saccharomyces cerevisiae (brewer's yeast). The added genes code for a transporter system embedded in the cell membrane that takes up cellulose chains (cellodextrins) and moves them inside the cell, where an enzyme called beta-glucosidase, which works like a molecular pair of scissors, chops up the chains into molecules of glucose that can then be fermented. Growing on cellulose, the modified yeast was able to produce ethanol (alcohol) with a yield of over 86%, close to the theoretical maximum achievable industrially when yeast is grown on glucose.

According to the researchers, "the addition of a cellodextrin transport system to biofuel-producing strains of yeast overcomes a major bottleneck to fermentation of lignocellulosic feedstocks and likely will help to make cellulosic biofuels economically viable."