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Researchers Modifying Corn With Genes to Produce Enzymes to Enable Simpler Production of Cellulosic Ethanol

Researchers at Michigan State University (MSU) are modifying the corn genome to enable the production of enzymes, within the corn biomass, needed to convert cellulose into fermentable sugar. This capability reduces the need for pretreatment of the biomass for the production of cellulosic ethanol. The transgenic corn plants produce these enzymes only in their leaves and stalk, and store them in sub-cellular compartments (the vacuoles).

The most recent version of the engineered corn—Spartan Corn III—now uses three enzymes from different sources: the thermophilic Acidothermus cellulolyticus E1 endo-cellulase; the fungal Trichoderma reesei (CBH1) exo-cellulase; and, the most recent addition, the microbial Butyrivibrio fibrisolvens H17c beta-glucosidase. MSU professor of crop and soil science Mariam Sticklen is presenting a talk on her team’s work at the 235th national meeting of the American Chemical Society this week in New Orleans, Louisiana.

The fact that we can take a gene that makes an enzyme in the stomach of a cow and put it into a plant cell means that we can convert what was junk before into biofuel.

—Mariam Sticklen

The first version of the corn—Spartan Corn I—added the endo-cellulase enzyme that cuts the cellulose into large pieces. Spartan Corn II added an exo-cellulase enzyme that breaks the cellulose pieces created by the first enzyme into sugar pairs.

Spartan Corn III uses the beta-glucosidase enzyme produced by a gene from the microbe in a cow’s rumen to separate pairs of sugar molecules into simple sugars. These single sugars are then readily fermentable into ethanol.

The DNA assembly of the animal stomach microbe required heavy modification in the lab to make it work well in the corn cells.

There are a lot of changes. We have to increase production levels and even put it in the right place in the cell.

—Mariam Sticklen

If the cell produced the enzyme in the wrong place, then the plant cell would not be able to function, and, instead, it would digest itself. One of the targets for the enzyme produced in Spartan Corn III is the vacuole of the cell. The enzyme will collect in the vacuole with other cellular waste products.

Because it is only in the vacuole of the green tissues of plant cells, the enzyme is only produced in the leaves and stalks of the plant, not in the seeds, roots or the pollen.

Sticklen’s research was funded by the US Department of Energy and Edenspace Systems Corp., the Consortium for Plant Biotechnology Research, and MSU Research Excellence Funds. The work will also be presented in the article “Plant Genetic Engineering for Biofuel Production: Towards Affordable Cellulosic Ethanol” in the June edition of Nature Reviews Genetics.

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Comments

Ray

Harvey D. explained it perfectly. It's sad our elected officials will never understand. We need to conserve and protect our food supply. We are already seeing the effects of rapidly rising food prices around the globe.

sjc

"Is there enough fertile land to produce all the cellulosic fuel..."

The short answer is yes and no. Let's say that the U.S. has 600 million acres in production and we devote half of them to cellulose fuels. Let's say that each acre can produce 5 tons of biomass and that you get 100 gallons per ton of liquid fuel. That is 500 gallons per acre times 300 million acres. That would be 150 billion gallons which is about how much gasoline we use each year.

So, yes we could do this, but no we probably will not. Even though those acres will grow corn, wheat, rice or other food crops and we are using just the stalks left over, we will probably not do this. It would take billions of dollars to build the 1000s of plants required to do this. Maybe even as much as what we spend in Iraq in one month...imagine that.

disgustedandamused

Actually, this is not a bad incremental step.
Are there better ultimate crops? Sure. Every part of the world needs biofuel crops best suited for their situation. Is corn the best ultimate biofuel crop for the US Midwest? No, but it's the one that is getting the temperate biofuels industry started here, and that's worth a lot. For that matter, ethanol is not the best alcohol for fuel -- butanol would be better for several reasons, I'll let someone push their favorite ultimate biofuel.
This takes the current main temperate biofuel crop, one with multiple products, and extends its usefulness for now. Industrial research does that -- it pays the bills for now, including the many steps along the long-term research path to get to that "ultimate biofuel".

I agree there isn't enough arable land to grow biofuels equivalent to current global or North American consumption. North America's economic, etc survival will require pluggable hybrids, sustainable electric generation AND storage, more efficient energy management in vehicles and fixed site use (including retrofits to our current building stock), and some frugality on our parts -- our best sustainable vehicles will be bicycles with good locks, until those PHEVs are standard-issue.
Even with most of our total vehicle-miles from sustainable electric generation, we'll still need bio or pyrolysis chemfuels "where the cords don't reach" -- including for agricultural machinery. That may be the practical production milestone for every country: can your farmers grow enough biofuels to get their other crops to market? If they can meet that, I'll make do with bicycles and subways if necessary.

Prof. Mariam Sticklen

I enjoyed reading all comments, questions and answers on my research. Please feel free to call me at 517-230-2929 should you wish to ask me questions directly.

Yes, those who wrote we do not have enough fertile land to plant non-food (replacing food crops) are correct. Also, U.S. already plants corn crop with not much use for corn leaves and stalks. So, using most of the already planted corn leaves and stalks for biofuels is the first step in biofuel production. What is important is that we have produced all three cellulases within the leaves and stalks cells, meanining that there would be no needs for production of enzymes in fermentors which require high energy input. These corn plants use the free energy of sun to produce these enzymes. Another advatage is that these enzymes are not produced in seeds, pollens or roots.

Randy

The concept of using corn for food and the stover for fuel is reasonable, except that the stover is usually plowed back into the field to limit the amount of additional nitrogen and related fertilizers needed for the high crop yields needed to make farming profitable.

Making the stover into fuel means more natural gas made into ammonia for the nitrogen fertilizer. NET NEGATIVE.

An alternative is to provide all tobacco farmers (and other crops as well) with sugar plants to make the easiest and cheapest ethanol (like Brazil) AND let teh farmers grow "life" (lower GHG fuel) rather than "death" (cancer, etc.) Also, sugar cane only needs replanting every two years, further saving fuel.

Chinedu

please keep me abreast with information on enzyme application in the industry, especially oil and gas industry.

i appreciate.

faithfully yours,
Hon.(Comr)E. C. C.Chinedu9(Rotr.)
The president,
National Association of Industrial Biochemistry Students, Federal University of Technology,
P.M. B.1526
Owerri, Imo State Nigeria.

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