A mutation could allow yeast to grow in higher-than-normal temperatures, paving the way for it to be more easily manufactured as vehicle fuel. The residual waste from the process could also potentially be used as a raw material, making it greener from a climate perspective.
If industrial yeast cultivation is not effectively cooled, the cells die from the heat they emit, Chalmers University of Technology reported. Today's yeast cultivation process must be cooled to 30 degrees in order to best produce ethanol. The process would be less expensive and more efficient if it only needed to be cooled to 40 degrees.
"As it turns out, a simple mutation is sufficient," said 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. "
Three yeast cultivations were exposed to a temperature of 40 degrees, after about 300 generations had passed the yeast started growing efficiently in all of the cultures. Upon analysis the researchers determined that while different mutations had occurred in the strains, all of them had the mutation that produced fecosterol.
"Since that mutation took place in three independent cultivations, it appears to be the most important factor in terms of the yeast becoming thermotolerant,"Nielsen said. "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. "
The findings could have major impacts on the bioethanol industry. Yeast-based ethanol production is currently valued at $100 billion per year, even the slightest improvement in the method could save billions.
"I believe that our results have very great potential for this type of development. In order to use residual waste of this kind, the substance lignocellulose must be broken down, which is difficult. The enzymes needed for decomposition work best at high temperatures." Nielsen said. "From a long-term perspective, our results may also increase the possibility of using yeast to produce more advanced biofuel that more closely resembles oil-based fuel."
The findings were published in a recent edition of the journal Science.
