A collaborative effort has produced a yeast strain that speeds up the process of making ethanol from cellulosic materials.
Researchers at the University of Illinois, Lawrence Berkeley National Laboratory, the University of California at Berkeley, Seoul National University and the oil company BP worked together to develop the newly engineered yeast strain that can simultaneously consume two types of sugar from plants to produce ethanol.
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 utilize in ethanol production. The new strain, made by combining, optimizing and adding to earlier advances, reduces or eliminates several major inefficiencies associated with current biofuel production methods.
“Xylose is a wood sugar, a five-carbon sugar that is very abundant in lignocellulosic biomass but not in our food,” said Yong-Su Jin, a professor of food science and human nutrition at Illinois and a principal investigator on the study. “Most yeast cannot ferment xylose.” A big part of the problem with yeasts altered to take up xylose is that they will suck up all the glucose in a mixture before they will touch the xylose, Jin said. A glucose transporter on the surface of the yeast prefers to bind to glucose. “It’s like giving meat and broccoli to my kids,” he said. “They usually eat the meat first and the broccoli later.”
The research objective was to develop a way for the yeast to quickly and efficiently consume both types of sugar at once, a process called co-fermentation. According to the researchers, 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. They say it is at least 20 percent more efficient at converting xylose to ethanol than other strains, making it “the best xylose-fermenting strain” reported in any study.