Scientists at the Department of Energy’s National Renewable Laboratory (NREL) have discovered a more efficient method of producing cellulosic biofuels. Deconstructing lignocellulosic biomass – plant matter such as corn stover – is currently done in two steps: a heat pretreatment and an enzyme deconstruction. But NREL Senior Scientists Yannick Bomble and Roman Brunecky have discovered a microorganism that allows them to skip a step in the ethanol conversion process.
“This is, in essence, a one-pot process,” said Bomble. “Pretreatment is expensive. If you can get better and better microbes and enzymes to bypass pretreatment, that’s a game-changer.”
Bomble, Brunecky and NREL Senior Research Fellow Michael Himmel published a paper detailing their work with caldicellulosiruptor bescii, a bacteria that thrive in high temperatures. The microorganism produces an enzyme called CelA, which deconstructs biomass to sugars. CelA also converts the sugars into ethanol.
The enzyme stands alone in its ability to break down cellulose fibers regardless of how crystalline they are, DOE says in a release. CelA also converts biomass to sugar much more quickly than other catalysts. The difference is CelA’s method of digging holes into the cellulose as compared to other enzymes which merely scrape away at the surface.
But the process is not yet perfected. It faces an immovable force in the plant binding material lignin, which renders CelA completely ineffective should it come into contact with the enzyme.
“When that happens, you lose the enzyme. The more enzymes you lose, the less efficient the conversion,” Himmel said. “That’s why we are coming up with strategies to remove that binding-to-lignin characteristic. Preserving the necessary binding to cellulose is something that we’re also working on.”
Enzyme AcCel5A, which comes from the hot-spring bacterium acidothermus cellulolyticus, weakens biomass by inserting a gene into the plant’s genome and then burrowing into its developing cell wall, creating nicks and voids that make biomass deconstruction easier. While similar enzymes have only stunted plant growth, AcCel5A has been successful at maintaining the amount of sugars yielded by the plant.
“We’re in a kind of challenging time. The question is, why aren’t the new second-generation commercial biorefinery plants functioning as planned?” Himmel asked. “In some cases, they’re using technology that we produced here decades ago, but now it’s old technology.”
The scientists hope their discoveries will bolster the biofuels industry, which has been diminished in recent years as gasoline prices have declined. Current research is focused on making biofuel production quicker, easier and more profitable.