Plant waste is available in large amounts and contains a mixture of complex sugars including hexoses and pentoses that can be fermented to alcohol.

As these feedstocks represent the biggest portion of processing costs, we need rapid and efficient conversion of all sugars present. At the moment there is a lack of microbes that will efficiently convert both hexoses and pentoses into ethanol.

—Dr. Weber

Bakers’ yeast—S. cerevisiae—is already used in the beverage industry to efficiently convert hexose sugars, such as glucose, into ethanol. By transferring genes from bacteria that naturally break down pentose, Dr Weber’s team have engineered S. cerevisiae to successfully ferment pentose and hexose sugars, thereby providing a higher yield of ethanol for the same amount of feedstock.

To enhance their biofuel potential even more, the yeast is being further modified to produce butanol instead of ethanol.

Butalco is a company started by Professor Boles together with Dr Gunter Festel that is developing a special technology to modify the yeast for pentose utilization and butanol production. In February, Butalco announced that it will use its proprietary new yeast technology to produce cellulosic ethanol from agricultural waste in a pilot plant in Southern Germany starting this summer. Butalco’s new microbial catalysts will enable up to 30% increased yields in cellulosic ethanol production, according to the company. (Earlier post.)