Jan 032011

Photo credit: Lawrence Berkeley National Laboratory - Roy Kaltschmidt

The biofuel industry stands to benefit from the development of a new variety of yeast which produces ethanol from plant products more efficiently.

Engineered by combining two existing yeast species, the new strain can simultaneously consume two types of sugar commonly found in plants to produce ethanol.

Researchers combined genes from one yeast species that naturally processes glucose – a six-carbon sugar that is relatively easy to ferment – and another that can process xylose – a five-carbon sugar that has been much more difficult to utilize in ethanol production.

Another breakthrough was achieved by finding a way for the organism to more efficiently process cellobiose, a complex sugar found in plant cell walls consisting of two linked glucose molecules.

The breakdown of cellobiose and the fermentation of xylose had previously been large stumbling blocks in efficient biofuel production.

The team from the University of Illinois, the Lawrence Berkeley National Laboratory, the University of California and energy company BP used the yeast species Saccharomyces cerevisiae as the building block for the research. This species has been used in baking and brewing for centuries and has already been utilized extensively in biofuel production. It is a relatively efficient fermenter of the sugar molecule glucose.

One of the factors limiting the efficiency of S. cerevisiae in biofuel production was its system of processing of cellobiose which consists of two glucose sugars linked together. Cellobiose was previously converted to glucose outside the yeast cell before entering through glucose transporters for conversion to ethanol. The researchers added a cellobiose transporter that allowed the yeast to transfer cellobiose directly into the cell for conversion to glucose then ethanol.

Another problem overcome was the inability of S. cerevisiae to process the complex sugar xylose, a common component of leaves and stems. To solve this hurdle three genes from the yeast species Picchia stipitis, a natural fermenter of xylose, were introduced.

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