A screening tool from the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) eases and greatly quickens one of the thorniest tasks in the biofuels industry: determining cell wall chemistry to find plants with ideal genes.
NREL's new High-Throughput Analytical Pyrolysis tool (HTAP) can thoroughly analyze hundreds of biomass samples a day and give an early look at the genotypes that are most worth pursuing. Analysis of a sample that previously took two weeks can now be done in two minutes. That is potentially game changing for tree nurseries and the biomass industry.
When it comes to making fuels out of trees, crops, grasses, or algae, it's all about the cell walls of the plants. Will they make it hard or easy for enzymes to turn the biomass into sugars? Differences in cell walls are enormous, and choosing the right ones can make the difference between a profit and a loss for tree growers, or between a fruitful or fruitless feedstock line for biomass companies.
Finding that particular species, or that individual tree, that has the genetic markers for the optimal biofuel candidate has heretofore been laborious and painstaking.
The Energy Independence and Security Act requires that the United States produce 21 billion gallons of non-corn-based biofuel by 2022. The market for biofuels is expected to grow steadily between now and then. Market analysts say the successful companies will be those that can steer their enzymes through the cell-wall structures in the easiest and most cost-effective ways, including by making changes in the structures themselves.
Tool can Pinpoint Phenotypes
To find out the chemical composition of the cell walls, companies have to sample large quantities of biomass, whether it's switchgrass, remnants of corn stalks, fast-growing trees, or algae.
The traditional strategy had been a multistep approach involving sample dissolution and chromatographic analysis, which can determine what the tree is composed of — but at the cost of disintegrating the sample.
NREL developed an approach using pyrolysis, analyzing the vapor from the samples produced by heat in the absence of oxygen, which is called high-throughput analysis pyrolysis, or HTAP. Pyrolysis destroys the sample, but the sample is tiny — four milligrams for the pyrolysis approach versus 10 grams for the traditional approach.
Difference in Signal Intensity Identifies Gene Manipulations
The lignin in a plant is crucial for its development and insect resistance, but it can stand in the way of enzymes that want to get at the sugars locked up in the carbohydrates. It's the deconstruction of the raw sugars that produces the sugars the biofuels industry finds valuable.
Lignin is a big molecule. Heating it up in the absence of oxygen — pyrolysis — breaks it down into smaller fragments that can be read by a molecular beam mass spectrometer.
The ratios of lignin to carbohydrate components, together with the intensity of the lignin peaks, can tell a scientist how easily a plant will give up its sugars.
HTAP integrates a molecular beam mass spectrometer with the pyrolysis unit to quickly determine chemical signatures (phenotypes) on small amounts of biomass samples that can be used for, among other things, identifying the genes controlling the chemical makeup.
Samples drop into the oven, where the pyrolysis creates a vapor that is read by the mass spectrometer — a chemical fingerprint. The auto-sampler quickly moves the samples into place and back out again, so the measurements can be taken every couple of minutes or so. Combining the HTAP chemical phenotypes with information such as genetic markers can signal there is a gene nearby that controls those chemical phenotypes — for better or worse.
HTAP can potentially reduce the amount of energy needed for ethanol production, said NREL's Mark Davis, principal investigator on the HTAP project. And that would make a huge difference in the marketplace.
NREL's Tool Combines Precision and Speed
The path toward an ultra-fast, ultra-sophisticated screening tool went through ArborGen, one of the nation's largest tree seedling suppliers. "They sent us some samples and asked, 'What can you tell us about them?'" Davis said.
Turns out, it was a lot more than ArborGen expected.
"We put the samples in our mass spectrometer, which looked at their genetic transformations and the associated cell-wall chemistry changes," Davis said. They discerned dozens of changes in transgenic biomass samples, each slight genetic tweak corresponding with a slight difference in the amount of lignin in the sample.
NREL was able to tell ArborGen that one sample had, say, half the lignin of another sample. "We were giving them information in a week that it took a month or two for them to get somewhere else," Davis said. "Not only that, but we were getting better information and greater chemical specificity and resolution than they had seen before."
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