Researchers Look to Grass to Make Gas

CLEMSON — Clemson University researchers focusing on switchgrass as a renewable fuel source are looking to fungi and bacteria—nature’s specialists in decomposing plants and animals into elements that can be reused to support life—to help make cost-competitive biofuels from plant biomass.

The process of breaking down the parts of plants that hold carbohydrates, cellulose and xylan, has been a tough problem to solve.

Most plant-based ethanol comes from the sugar and starch in corn and sugarcane. Biomass—vegetation and plant-based waste used to make energy—remains too costly to be competitive with oil and gas.

That's partly because production involve releasing the cellulose and xylan from lignin, the substance that binds the cells and structures in woody plants. Xylan is a gummy substance in plant cell walls made from the sugar xylose. Lignin often is removed as a pretreatment step in biofuel production before microbes convert cellulose and xylan to the sugars glucose and xylose. The sugars are fermented to produce alcohol-based fuels.

Microbiologist Mike Henson is part of the Clemson team studying how to free up the carbohydrates in switchgrass and waste paper. Henson’s work involves identifying the right bacteria and fungi and the right enzymes that will break down the carbohydrates and xylans to release plant sugars.

Success means more than coming up with energy alternatives. It also will help the environment, particularly atmospheric conditions, and advance a sustainable bio-economy based on "real-time" renewable energy instead of fossil fuels that store long-ago energy from the sun.

“It’s not going to be just one organism or just one enzyme,” Henson said. The fungi and the bacteria work additively as a community. The enzyme will be more like an “enzyme cocktail.”

Figuring out the enzymes is a big deal. Enzymes are biological substances — proteins — that set into motion complex reactions in living organisms. Enzymes do very specific tasks, meaning that Henson has to not only find the right enzymes, but they have to be triggered in the right order so that each does its part at the right time.

Simplified, the enzyme process involves four stages:

1. An enzyme and keyed-to molecule have to find each other.
2. The enzyme links to the molecule at a made-to-fit location called the “active site.”
3. Catalysis occurs, setting off a change in the enzyme-linked molecule, breaking it down or enabling it to combine with another molecule, creating what scientists call the “product.”
4. Finished doing the task, the enzyme delinks from the molecule and is ready to act again.

Henson’s work can aims to reduce the expense of making ethanol from biomass, getting costs down to $3 to $4 per gallon making it competitive with gasoline and diesel fuel.