Currently used as a fuel additive to improve gasoline combustibility, ethanol is often touted as a potential solution to the growing oil-driven energy crisis. But there are significant obstacles to producing ethanol: One is that high ethanol levels are toxic to the yeast that ferments corn and other plant material into ethanol.
By manipulating the yeast genome, M.I.T researchers have engineered a new strain of yeast that can tolerate elevated levels of both ethanol and glucose, while producing ethanol faster than un-engineered yeast.
Fuels such as E85, (85% ethanol), are becoming common in states where corn is plentiful; however, their use is mainly confined to the Midwest because corn supplies are limited and ethanol production technology is not yet efficient enough.
Better efficiency has been an elusive goal, but the M.I.T. researchers took a new approach, led by Hal Alper, a postdoctoral associate in the laboratories of Professor Gregory Stephanopoulos of chemical engineering and Professor Gerald Fink of the Whitehead Institute.
The traditional way to genetically alter a trait, or phenotype, of an organism is to alter the expression of genes that affect the phenotype. But for traits influenced by many genes, it is difficult to change the phenotype by altering each of those genes, one at a time.
The key to the M.I.T. strategy is manipulation of the genes encoding proteins responsible for regulating gene transcription. Targeting the transcription factors can be a more efficient way to produce desirable traits. "It is the makeup of the transcripts that determines how a cell is going to behave and this is controlled by the transcription factors in the cell," according to Stephanopoulos.
The M.I.T. team is the first to use this new approach, which is akin to altering the central processor of a computer (transcription factors) rather than individual software applications (genes), says Fink, an M.I.T. professor of biology and a co-author on the paper.
The high-ethanol-tolerance yeast also proved to be more rapid fermenters: The new strain produced 50% more ethanol during a 21-hr period than normal yeast.
The prospect of using this approach to engineer similar tolerance traits in industrial yeast could dramatically impact industrial ethanol production, a multi-step process in which yeast plays a crucial role. First, cornstarch or another polymer of glucose is broken down into single sugar (glucose) molecules by enzymes, then yeast ferments the glucose into ethanol and carbon dioxide.
The Dept. of Energy says four billion gallons of ethanol were produced from 1.43 billion bushels of corn grain (including kernels, stalks, leaves, cobs, and husks) in the U.S., according to. In comparison, the U.S. consumed about 140 billion gallons of gasoline.