Purdue's genetically altered yeast allows about 40 percent more ethanol to be made from sugars derived from agricultural residues, such as corn stalks and wheat straw, compared with "wild-type" yeasts that occur in nature.
The agricultural residues are primarily made up of cellulose and "hemicellulose," which are known as cellulosic materials. Unlike traditional ethanol feedstocks, such as corn kernels, the cellulosic materials contain two major sugars, glucose and xylose, which cannot both be fermented into ethanol by natural Saccharomyces yeast, the microorganism used by industry to produce ethanol, said Nancy Ho, a senior research scientist and leader of the molecular genetics group in Purdue's Laboratory of Renewable Resources Engineering, or LORRE.
Iogen specializes in producing ethanol from cellulosic material.
A team led by Ho developed the more efficient yeast during the 1980s and 1990s. Conventional yeast can ferment glucose to ethanol, but it cannot ferment xylose. Xylose makes up about 30 percent of the sugar from agricultural residues, and the inability to ferment xylose would represent a major loss of ethanol yield, Ho said.
The Purdue researchers altered the genetic structure of the yeast so that it now contains three additional genes that make it possible to simultaneously convert glucose and xylose to ethanol. The ability to ferment xylose increases the yield of ethanol from straw by about 40 percent. Being able to simultaneously ferment glucose and xylose is important because both sugars are found together in agricultural residues, Ho said.