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Corn stover can produce a high volume of biofuels

Experts have demonstrated an efficient method for boosting yeast to make biofuels from corn stover, the parts of a corn plant that are typically discarded.

Only a small portion of a corn plant is actually used, and the rest is discarded as waste. If the leftover leaves, stalks and cobs could be fermented into ethanol like corn kernels, the corn stover could be a large-scale, renewable source of fuel.

Study co-author Gerald Fink is a professor at the Massachusetts Institute of Technology (MIT) and a member of the Whitehead Institute for Biomedical Research.

“Stover is produced in huge amounts, on the scale of petroleum,” said Professor Fink. “But there are enormous technical challenges to using them cheaply to create biofuels and other important chemicals.”

In collaboration with Professor Gregory Stephanopolous, Professor Fink changed the growth medium conditions of the baker’s yeast Saccharomyces cerevisiae. The experts demonstrated that the modified yeast could be used to produce ethanol and plastics from corn stover. 

The biofuels industry relies on organisms such as yeast to convert the sugars glucose, fructose and sucrose in corn kernels to ethanol, which can be mixed with traditional gasoline to fuel vehicles.

Corn stover are full of sugars that can also be converted into biofuels, but the plants hold on to the cellulose molecules very tightly. An acidic solution can be used to help break down the tough casings that hold the sugars, but a consequence of using the acid is the production of molecules called aldehydes, which are toxic to yeast.

“These toxins are one of the biggest limitations to producing biofuels at a low cost.” said Professor Stephanopoulos. To address the issue of aldehydes, the researchers decided to focus on the aldehydes produced when acid is added to break down tough molecules. 

“We don’t know the exact mechanism by which aldehydes attack microbes, so then the question was, if we don’t really know what it attacks, how do we solve the problem?” Lam said. “So we decided to chemically convert these aldehydes into alcohol forms.”

Ultimately, this method was combined with the newly modified yeast. “We essentially channeled the aldehyde problem into the alcohol problem, which we had worked on before,” said Lam. “We changed and detoxified the aldehydes into a form that we knew how to handle.”

The researchers were able to efficiently make ethanol and even plastic precursors from corn stover, miscanthus and other types of plant matter. 

“We were able to produce a high volume of ethanol per unit of material using our system,” said Professor Fink. “That shows that there’s great potential for this to be a cost-effective solution to the chemical and economic issues that arise when creating fuel from cellulose-rich plant materials.”

The study is published in the journal Science Advances.

By Chrissy Sexton, Staff Writer

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