Researchers at the Energy Department’s National Renewable Energy Laboratory (NREL) have discovered an enzyme that digests cellulose almost twice as fast as the current leading enzyme on the market.

NREL researchers first discovered the enzyme in a microorganism found in the Valley of Geysers on Russia’s Kamchatka Peninsula in 1990.  The team’s paper “Revealing Nature’s Cellulase Diversity: The Digestion Mechanism of Caldicellulosiruptor bescii CelA” has been published in the journal Science.

If the new enzyme continues to perform well in larger tests, it could help drive down the price of making lignocellulosic fuels, such as ethanol on to other biofuels that can be dropped into the existing fuel infrastructure.

The bacterium Caldicellulosiruptor bescii was first found in heated freshwater pools. It secretes the cellulase, (group of enzymes that work on cellulose) CelA, which has the complex arrangement of two catalytic domains separated by linker peptides and cellulose binding modules. The bacteria secreting the promising CelA thrive in temperatures of 75 to 90º Celsius (167-194º Farenheit).

The NREL researchers put CelA to the test and found that it produced more sugars than the most abundant cellulase in the leading commercial mixtures, Cel7A, when acting on Avicel, a material that is an industry standard to test cellulose degradation. They found that CelA not only can digest cellulose in the more common surface removal way, but that it also creates cavities in the material, which leads to greater synergy with more conventional cellulases, resulting in higher total sugar release.

One of the papers authors, NREL Scientist Yannick Bomble begins the explanation with, “Microorganisms and cellulases operating at such high temperatures have several biotechnological advantages.”

“CelA is the most efficient single cellulase we’ve ever studied – by a large margin,” Bomble said. “It is an amazingly complex enzyme, combining two catalytic domains with three binding modules. The fact that it has two complementary catalytic domains working in concert most likely makes it such a good cellulose degrader.”

In industrial applications for most commercial operations using enzyme cocktails, a combination of 15 to 20 different enzymes turn plant material into the sugars that are valuable to the biofuels industry. In most such cocktails, one type of enzyme, Cel7A, does the largest amount of work.

When researchers compared the new CelA to Cel7A, they discovered that at its optimal temperature of 50º Celsius (122º F), Cel7A achieves only 50% of the performance of CelA when converting the Avicel.

CelA was first discovered 15 years ago, but until this recent work, all that was known about this complex protein was its general architecture and that it had the ability to degrade cellulose.

The organism was initially grown on biomass by scientists from the University of Georgia and was used to produce extracellular enzymes (enzymes that function outside of the cell). Those extracellular enzymes later were purified and characterized at NREL using techniques including performance assays, advanced imaging, X-ray crystallography, and modeling on supercomputers.

NREL scientists found that CelA is not only very active on cellulose, but also attacks xylose. That could mean that levels of enzymes that specialize in removing xylose in commercial cocktails could be lowered, translating to lower costs.

When an enzyme produces sugars more efficiently, it means lower costs for the enzyme cocktail, which is a major expense component in the process of converting biomass into fuel.

The findings have important implications for industry and are also fascinating for the scientists. “We are learning a lot about the evolution of these cellulases, how they can thrive in extreme environments, and how they operate on biomass,” NREL scientist and the paper’s lead author, Roman Brunecky, said.

“This discovery could reshape the landscape of commercial cellulase cocktail design,” said Paul Gilna, director of the BioEnergy Science Center, which provided the funding for this work. It is one of three Bioenergy Research Centers supported by the Office of Biological and Environmental Research in Energy Department’s Office of Science.

Lots of optimism is in play and as of yet no estimates of the cost of producing CelA as its quite early in the research stage.  There is sure to be intense attention given to CelA as the new enzyme offers more sugar, and much faster production timing.

Its still going to be about price at the shipping point for cellulosic based fuels.


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