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MIT Engineered Yeast Improves Ethanol Production

7 December 2006

MIT scientists have engineered yeast that can improve the speed and efficiency of ethanol production. By manipulating the yeast genome, the 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. The work is reported in the Dec. 8 issue of Science.

The MIT strategy is to manipulate the genes encoding proteins responsible for regulating gene transcription and, in turn, controlling the repertoire of genes expressed in a particular cell. These types of transcription factors bind to DNA and turn genes on or off, essentially controlling what traits a cell expresses.

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.

Targeting the transcription factors instead 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.

—Gregory Stephanopoulos,co-author

The MIT researchers are the first to use this new approach. In this case, the researchers targeted two different transcription factors. They got their best results with a factor known as a TATA-binding protein, which when altered in three specific locations caused the over-expression of at least a dozen genes, all of which were found to be necessary to elicit an improved ethanol tolerance, thus allowing that strain of yeast to survive high ethanol concentrations.

Because so many genes are involved, engineering high ethanol tolerance by the traditional method of overexpressing individual genes would have been impossible, according to Hal Alper, a postdoctoral associate in the laboratories of Professor Gregory Stephanopoulos. Furthermore, the identification of the complete set of such genes would have been a very difficult task, Stephanopoulos adds.

The high-ethanol-tolerance yeast also proved to be more rapid fermenters: The new strain produced 50% more ethanol during a 21-hour 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 research was funded by the DuPont-MIT Alliance, the Singapore-MIT Alliance, the National Institutes of Health and the US Department of Energy.

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December 7, 2006 in Biotech, Ethanol | Permalink | Comments (8) | TrackBack (0)

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Permit me to qualify what I am about to write:

I know very little about the production of ethanol via fermentation. I have done it and distilled the result into high proof (something) which I drank. I recall reading somewhere during those times that the increasing alcohol shut down fermentation, thereby limiting the amount of alcohol you could brew in a given volume.

I wonder if it is possible to somehow continuously remove alcohol during the fermentation process until most of the feedstock is depleted? This would significantly improve the efficiency of the process.

Any thoughts?

Lucas, what you are referring to is reactive distillation. Its a good idea. This approach is used with conventional chemical processes. The difficulty with ethanol production is that fermentation takes place at moderate temperatures, while distillation, azeotropic in this case, needs higher temperatures even under vacuum. Making yeast tolerent of higher temperatures may make this type of process possible.

Faster production means a setup that makes 100 gallons of C2H5OH can produce 150 ga. The equipment would be the same, but they can cram higher concentrations of sugar/starches into a batch, and get more ethanol from it. The batches would have roughly the same amount of water, hence there could be some savings due to distilling more alcohol, from a same quantity of liquid.
_On the alcoholic beverage front, higher proof beers and other drinks, could be had without distillation. 44+ proof drinks would need less distillation to achieve desired end product. All this would save energy.

Ethanol boiling point is 78C at normal atmospheric pressure. However, this temperature could be significantly reduced by applying some vacuum – practice commonly used in distillation processes. So, with some more heat tolerant yeast, continuous fermentation/distillation is not impossible.

It would be neat if we had some sort of selective filter. One that would pass alcohol but not water or glucose.


Or some heavy or lighter additive that the alcohol would bind with and then be separated out, allowing the fermentation to continue until all the sugars were consumed.

A layer of vegetable oil will let ethanol pass through it but not water.
The problem is that the solution must be kept below 78C to preserve the integrity of the oil layer. This requires a large horizontal area compare to a traditional system.

Tom Deplume,
Nice, but unless removed and replenished with new oil, the vegetable oil will could go rancid.

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