Yeast is an inexpensive means to transform corn and other promising crops into biofuels like ethanol. However, too much ethanol can be toxic to yeast, which severely limits the production capacity of the microbial fungi. Now, researchers from MIT are saying that they have solved the toxicity riddle, developing a strategy that allows yeast to make ethanol en masse without suffering the consequences.
"Toxicity is probably the single most important problem in cost-effective biofuels production," Gregory Stephanopoulos, a chemical engineer at MIT, said in a recent statement.
According to a new study published in the journal Science, Stephanopoulos and colleagues at MIT and the Whitehead Institute for Biomedical Research have identified a new way to boost yeast's tolerance of ethanol by simply altering the environment in which it is grown. This new strategy comes with a greater understanding of why ethanol and other alcohols are toxic to yeast in the first place, and can pave the way for future biofuel work.
"The more we understand about why a molecule is toxic, and methods that will make these organisms more tolerant, the more people will get ideas about how to attack other, more severe problems of toxicity," added Stephanopoulos, the study's senior author.
Stephanopoulos and his colleague initially set out to tackle the toxicity problem genetically, targeting groups of genes that could be manipulated to help yeast become more tolerant to ethanol. However, this proved largely unsuccessful until the team started trying to change the characteristics of the yeast by changing the environment it was grown in.
Amazingly, this proved to be the exact strategy they needed, making yeast more resistant to toxicity without influencing its natural biochemical pathways used to produce ethanol.
The process that makes yeast more resistant is fairly straight forward. Yeast are protected by their cell membranes, but the ethanol they produce slowly eats away at this coating, eventually disrupting the process that produces ethanol in the first place. By having yeast grow in an atypical environment, the researchers found a way to encourage the development of a thicker and stronger membrane, allowing the yeast to work its magic for much longer.
"We're energizing yeast to allow them to withstand harsher conditions and continue production. What's also exciting to us is that this could apply beyond ethanol to more advanced biofuel alcohols that upset cell membranes in the same way," explained Felix Lam, the study's lead author.
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