A corny turn for biofuels from switchgrass

Nov 18, 2011
This image shows the overxpression of the Cg1 gene in switchgrass (left) compared to Wild-type of switchgrass of the same age and grown under the same conditions. Credit: Photo courtesy of USDA/ARS

Many experts believe that advanced biofuels made from cellulosic biomass are the most promising alternative to petroleum-based liquid fuels for a renewable, clean, green, domestic source of transportation energy. Nature, however, does not make it easy. Unlike the starch sugars in grains, the complex polysaccharides in the cellulose of plant cell walls are locked within a tough woody material called lignin. For advanced biofuels to be economically competitive, scientists must find inexpensive ways to release these polysaccharides from their bindings and reduce them to fermentable sugars that can be synthesized into fuels.

An important step towards achieving this goal has been taken by researchers with the U.S. Department of Energy (DOE)'s Joint BioEnergy Institute (JBEI), a DOE Center led by the Lawrence Berkeley National Laboratory (Berkeley Lab).

A team of JBEI researchers, working with researchers at the U.S. Department of Agriculture's Agricultural Research Service (ARS), has demonstrated that introducing a maize (corn) gene into switchgrass, a highly touted potential feedstock for advanced biofuels, more than doubles (250 percent) the amount of starch in the plant's cell walls and makes it much easier to extract polysaccharides and convert them into fermentable sugars. The gene, a variant of the maize gene known as Corngrass1 (Cg1), holds the switchgrass in the juvenile phase of development, preventing it from advancing to the adult phase.

"We show that Cg1 switchgrass biomass is easier for enzymes to break down and also releases more glucose during saccharification," says Blake Simmons, a chemical engineer who heads JBEI's Deconstruction Division and was one of the for this research. "Cg1 switchgrass contains decreased amounts of lignin and increased levels of glucose and other sugars compared with wild switchgrass, which enhances the plant's potential as a feedstock for advanced biofuels."

The results of this research are described in a paper published in the Proceedings of the National Academy of Sciences (PNAS) titled "Overexpression of the maize Corngrass1 microRNA prevents flowering, improves digestibility, and increases starch content of switchgrass."

Lignocellulosic biomass is the most abundant organic material on earth. Studies have consistently shown that biofuels derived from lignocellulosic biomass could be produced in the United States in a sustainable fashion and could replace today's gasoline, diesel and jet fuels on a gallon-for-gallon basis. Unlike ethanol made from grains, such fuels could be used in today's engines and infrastructures and would be carbon-neutral, meaning the use of these fuels would not exacerbate global climate change. Among potential crop feedstocks for advanced biofuels, switchgrass offers a number of advantages. As a perennial grass that is both salt- and drought-tolerant, switchgrass can flourish on marginal cropland, does not compete with food crops, and requires little fertilization. A key to its use in biofuels is making it more digestible to fermentation microbes.

"The original Cg1 was isolated in maize about 80 years ago. We cloned the gene in 2007 and engineered it into other plants, including switchgrass, so that these plants would replicate what was found in maize," says George Chuck, lead author of the PNAS paper and a plant molecular geneticist who holds joint appointments at the Plant Gene Expression Center with ARS and the University of California (UC) Berkeley. "The natural function of Cg1 is to hold pants in the juvenile phase of development for a short time to induce more branching. Our Cg1 variant is special because it is always turned on, which means the plants always think they are juveniles."

George Chuck and Sarah Hake, plant molecular geneticists at the Plant Gene Expression Center, Albany, California, introduced a variant corngrass gene into switchgrass. Credit: Photo courtesy of USDA/ARS

Chuck and his colleague Sarah Hake, another co-author of the PNAS paper and director of the Plant Gene Expression Center, proposed that since juvenile biomass is less lignified, it should be easier to break down into fermentable sugars. Also, since juvenile plants don't make seed, more starch should be available for making biofuels. To test this hypothesis, they collaborated with Simmons and his colleagues at JBEI to determine the impact of introducing the Cg1 gene into switchgrass.

In addition to reducing the lignin and boosting the amount of starch in the switchgrass, the introduction and overexpression of the maize Cg1 gene also prevented the switchgrass from flowering even after more than two years of growth, an unexpected but advantageous result.

"The lack of flowering limits the risk of the genetically modified switchgrass from spreading genes into the wild population," says Chuck.

The results of this research offer a promising new approach for the improvement of dedicated bioenergy crops, but there are questions to be answered. For example, the Cg1 switchgrass biomass still required a pre-treatment to efficiently liberate fermentable sugars.

"The alteration of the switchgrass does allow us to use less energy in our pre-treatments to achieve high sugar yields as compared to the energy required to convert the wild type plants," Simmons says. "The results of this research set the stage for an expanded suite of pretreatment and saccharification approaches at JBEI and elsewhere that will be used to generate hydrolysates for characterization and fuel production."

Another question to be answered pertains to the mechanism by which Cg1 is able to keep switchgrass and other plants in the juvenile phase.

"We know that Cg1 is controlling an entire family of transcription factor genes," Chuck says, "but we have no idea how these genes function in the context of plant aging. It will probably take a few years to figure this out."

Explore further: Battling superbugs with gene-editing system

Related Stories

A new tool for improving switchgrass

Jul 27, 2010

Agricultural Research Service (ARS) scientists have developed a new tool for deciphering the genetics of a native prairie grass being widely studied for its potential as a biofuel. The genetic map of switchgrass, published ...

Recommended for you

Project launched to study evolutionary history of fungi

2 hours ago

The University of California, Riverside is one of 11 collaborating institutions that have been funded a total of $2.5 million by the National Science Foundation for a project focused on studying zygomycetes – ancient li ...

Different watering regimes boost crop yields

5 hours ago

Watering tomato plants less frequently could improve yields in saline conditions, according to a study of the impact of water and soil salinity on vegetable crops.

Woolly mammoth genome sequencer at UWA

7 hours ago

How can a giant woolly mammoth which lived at least 200,000 years ago help to save the Tasmanian Devil from extinction? The answer lies in DNA, the carrier of genetic information.

Battling superbugs with gene-editing system

Sep 21, 2014

In recent years, new strains of bacteria have emerged that resist even the most powerful antibiotics. Each year, these superbugs, including drug-resistant forms of tuberculosis and staphylococcus, infect ...

User comments : 4

Adjust slider to filter visible comments by rank

Display comments: newest first

Shootist
1 / 5 (3) Nov 18, 2011
Really? You have to use petroleum to fuel the power plants to make the electricity that melts the aluminum, steel and glass for the building you'll use to process this pixie dust.

You'll have to use coal/gas/petroleum power to manufacture the vehicles that take the pixie dust from field to plant to distributor. And the tankers used to transport the pixie dust to market run on diesel.

Your final product has 1/2 the energy content, by weight, of gasoline.

Pixie dust always take more energy to manufacture than it will release when burned. Why would you use an energy sink as a source of energy?

Maybe we should try some other type of unobtainium. Di-lithium crystals, anyone? Antimatter? Bathing in the glow of our Ultimate Leader?
Shakescene21
5 / 5 (3) Nov 19, 2011
@Shootist - Did you know it takes a lot of coal/gas/petroleum to manufacture the machinery that mines, transports, and refines oil into gasoline? Using your logic, gasoline is an energy sink the same as biofuels.

Switchgrass-based biofuels might solve many of our environmental and economic problems, a lot of them caused by our appetite for gasoline, and we are fortunate that DOE is trying to advance this opportunity.
Burnerjack
1 / 5 (1) Nov 19, 2011
Can't methanol be made from ANY organic decomposing matter? One thing the world in abundance is garbage and sewerage. Could there be a cheaper feed stock? While methane IS a powereful greenhouse gas, is it still after it's burned? With such a simple solution available, is it just the business of politics and vice-versa? Why just the crap coming out of DC could....
yoatmon
not rated yet Nov 20, 2011
Can't methanol be made from ANY organic decomposing matter?

AUDI just commissioned a 1.5 MW pilot project plant in Stuttgart, Germany. The produced electric power is used to electrolyze Water into O2 and H2. CO2 is extracted from the atmosphere and - employing a special catalyzer - combined chemically with the H2 to produce methane. Methane is, for all tends and purposes, identical with NG; it can be stored together with NG and can be used either directly in ICE's or in bio-gas power plants for power production. This is an effective method for utilizing and buffering surplus reg. energy (PV or wind); either use has a carbon-neutral footprint. A further 10 MW plant has been contracted from AUDI.