Biofuels are a hot commodity these days, with ethanol being one of the most popular. However, ethanol has a problem: Yeast. Though instrumental to its creation, yeast can be fickle. Get it too hot, or concentrate the ethanol too highly, and the yeast shut down, limiting production potential. Now, according to separate research by MIT and Chalmers University of Technology, science has engineered ways to make yeast more tolerant of both booze and heat.

The issue, at least with regards to ethanol and yeast, is toxicity. Ethanol breaks down and eventually penetrates cell membranes, killing the yeast. As part of the solution, the MIT team looked to the medium in which the yeast is grown. Simply adding potassium and hydrogen ions to the medium helped the yeast compensate for higher ethanol concentrations. The fix boosted production by 80%.

“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,” says Gregory Stephanopoulos, one of the senior authors of the Science paper.

Heat is also a problem for ethanol-producing yeast. The yeast perform best at 30 degrees Celsius, but unfortunately it’s expensive and inefficient to artificially maintain that lower temperature. Cost savings would be significant if the yeast could operate at a more reasonable 40 degrees Celsius without deteriorating. It would also be more efficient, as the raw materials  used to fuel yeast break down at higher temperatures. Fortunately, researchers at Chalmers University of Technology found a relatively easy solution.

”As it turns out, a simple mutation is sufficient,” says Jens Nielsen, professor of systems biology and head of the research team. ”Yeast has a molecule in its cell membrane called ergosterol, instead of cholesterol which humans have. The mutation exchanges ergosterol for a more bent molecule called fecosterol. This has several different effects on the cells, which enables the yeast to grow at 40 degrees. ”

Rather than engineering the mutation, the researchers allowed it to happen naturally through accelerated laboratory evolution. After three months and 300 generations of being exposed to the higher temperatures, the yeast suddenly began to thrive in all three experimental cultures.

”Since that mutation took place in three independent cultivations, it appears to be the most important factor in terms of the yeast becoming thermotolerant,” says Nielsen. ”This shows how rapidly evolution can change an organism. It is interesting that the structure in fecosterol is the same as in sterol-like molecules, which protect some bacteria and plants against high temperatures.”