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NREL enzyme enables conversion of biomass to sugar up to 14x faster than current alternatives; changing the economics of conversion

13 January 2015

Scientists at the US Department of Energy’s (DOE) National Renewable Energy Laboratory (NREL) have developed an enzyme that can enable the conversion of biomass to sugars up to 14 times faster and more cheaply than competing catalysts in enzyme cocktails today. The enzyme called CelA, a cellulase from the bacterium Caldicellulosiruptor bescii, could thus could change the economics of biofuel conversion.

In one scenario, the best commercially used enzyme converted sugars at a 30% extent in seven days. CelA converted to double that extent. And while it took the alternative enzyme seven days to achieve that conversion, CelA, with a small boost from an extra beta glucosidase, achieved double in just about two days. Among CelA’s many attributes:

  • Biomass comprises three types of polymers that are intermeshed to form plant cell walls: cellulose, xylan, and lignin. Each of the three polymers typically requires several types of enzymes to deconstruct them to soluble species that can then be upgraded to ethanol, drop-in fuels, or chemicals. But unlike most catalysts which digest one major component in biomass, CelA can digest two: both cellulose and xylan.

  • CelA works in two mechanical realms, not just one. It is an ablater, scraping the valuable material off the cell walls of the plants. But it is also a borer, digging deep into the wall to grab more of the digestible biomass. It is the only enzyme known to dig pits into biomass; others only ablate.

  • It can operate at much higher temperatures than other enzymes; higher temperatures mean faster action.

  • CelA also works faster on raw biomass than on biomass pre-treated with chemicals.

  • Because it can operate above the boiling point of alcohol, the alcohol is separated naturally, saving a costly step in the conversion process—and the high temperatures kill many of the microorganisms that would otherwise interfere with the process.

20150112_cela_cartoon_large
Using electron microscopy, the NREL researchers and their partners at the University of Georgia found that CelA not only ablates the cell wall of lignocellulosic biomass, but excavates cavities into the surface.

Conventional cellulases such as Cel7A (left side of figure) use a surface ablation strategy to deconstruct cellulose, converting single layers of cellulose strands. CelA (right side) utilizes both this surface ablation strategy as well as an entirely new pit-formation mechanism to excavate down into the cellulose strands. Image by Bryan Donohoe, NREL. Click to enlarge.

If you can achieve in one day what typically takes seven, you are saving the better part of a week of processing. And that can have a huge economic impact.

—Senior Scientist Roman Brunecky

CelA alone is four to five times faster at breaking down sugars than the enzymes in today’s cocktails. A more typical usage would be CelA combined with a beta glucosidase—an improvement that makes it 14 times faster.

If the enzyme continues to perform well in larger tests, it could help drive down the price of converting cellulose and, with it, the price of everything from jet fuel to ethanol, butanol, drop-in fuels, and numerous chemicals. NREL has filed for patent protection on the enzyme formulation and the improvements made to the unusual enzyme.

The discovery was the unexpected result of very thorough imaging and analysis by Bryon Donohoe of NREL’s Biomass Surface Characterization Laboratory research team.

C. bescii, producer of the CelA enzyme, was first discovered in warm-water pools in the Valley of Geysers on Russia’s Kamchatka Peninsula in the 1990s. Russian scientists found the enzyme somewhat promising, but it wasn’t until the NREL researchers conducted a thorough analysis and added improvements that its potential was realized.

NREL found some surprising properties. For example, even though CelA contains naturally occurring endoglucanase, the researchers found that adding more of the substance greatly accelerated the rate at which it broke down sugars.

CelA has its own beta-glucosidase activity, but NREL researchers checked to see how it would perform if more of the beta-glucosidase was added. That’s when the rate really accelerated.

You’d think that nature would already have evolved an optimal mix in a single enzyme. You expect to see maybe a 20% to 30% improvement when you add a beta glucosidase to a cocktail—not the doubling or tripling of the rate of conversion and the increase of rates by a factor of 10 that we got with CelA. Nobody expected the improvement to be this high.

—Roman Brunecky, NREL and lead author of a paper on CelA in Science

In a Perspective on a 2013 paper in Science describing CelA’s digestion mechanism, Alex Berlin of biotechnology company Novozymes noted that CelA’s ability to operate at high temperatures “would be seen by many in the biomass biorefinery industry as an advantage” because it “dramatically reduces the chances of bacterial contamination” while lowering the viscosity of the mixtures.

Acting alone or in combination with a β-glucosidase, CelA breaks down highly recalcitrant cellulose faster than does an enzyme mixture commonly used in commercial biomass enzyme products. Furthermore, CelA shows higher specific activity on raw biomass than on physicochemically pre-treated biomass. These results may be a turning point in the development of future bioconversion technologies that do not require biomass pretreatment or the participation of a large number of enzyme components.

—Berlin (2013)

The NREL researchers are examining the other enzymes secreted by C. bescii. They’re also using what they’ve learned from CelA to help improve cellulase enzymes that are more compatible with the enzyme formulations used today.

The next step toward using CelA at commercial scale is to express large amounts of the enzyme in existing production systems, and to boost enzyme yields from the native organism, C. bescii.

Resources

  • Roman Brunecky, Markus Alahuhta, Qi Xu, Bryon S. Donohoe, Michael F. Crowley, Irina A. Kataeva, Sung-Jae Yang, Michael G. Resch, Michael W. W. Adams, Vladimir V. Lunin, Michael E. Himmel, and Yannick J. Bomble (2013) “Revealing Nature’s Cellulase Diversity: The Digestion Mechanism of Caldicellulosiruptor bescii CelA” Science 342 (6165), 1513-1516 doi: 10.1126/science.1244273

  • Alex Berlin (2013) “No Barriers to Cellulose Breakdown” Science 342 (6165), 1454-1456. doi: 10.1126/science.1247697

January 13, 2015 in Biomass, Fuels | Permalink | Comments (9) | TrackBack (0)

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If it could work at scale, this could be one of the best renewable energy sources around. Imagine how much cellulosic waste is available from both industry, agriculture, and consumer trash (that would normally see its end of life in a landfill.)

This sounds like Mr Fusion in a way. The alcohol will naturally evaporate, this could mean an endless batch kind of processing... Leave the enzymes in the tank and just shovel in more fibers.

I'm just curious to see how long this takes to get to market. If its really effective, we could see it trying to compete with sub $50 a barrel crude. Benefiting nearly every economy that relies on petroleum.

The gains in alternative energy in just the past six years of Obama support may be his greatest legacy.

Just further commercialize before someone else takes credit.

A major expenditure on cellulose ethanol facilities is the conversion section, where lots of cellulose and enzymes convert to sugars. This takes up space and resources in the pipeline.

If this is commercially viable, the four cellulose plants in the U.S. could process more at a faster pace, making the investment payback sooner. There are lot of advances that the Recovery Program and national labs have made in the last 6 years. Some are too busy criticizing to notice.

This will really be something if it works out.
Scale up and lets see what really happens.

The timing is bad with $45 oil, but this is a temporary phase (I hope) but it will probably take a few years to scale so they could be OK.

Might put a ceiling on oil prices, though.
At least it is recycling carbon from Biomass, not fossil carbon.

With enough HEV/PHEV FFV running cellulose ethanol, we can tell OPEC to keep their oil. If you think oil will remain at these prices for long, think again.

Here we are talking! That is what we call a breakthrough, might be a game changer if this enzyme can be mass produced for cheap...

If the bacteria can grow undisturbed in the vat/refinery throughout the whole process, like I think they say, this could be very lucrative. Thus each refinery creates a feedstock to seed other refineries.

If the bacteria's only excrement is ethanol/other alcohol, and it isn't easily poisoned or poisoned at all by what enters the system it would just make sense on having a community of the organisms be perpetual throughout the process.

Imagine if the concentrations were enough that we could seed a refinery in each region and use it as a sink for cellulose waste. Then eventually overtime the concentrations would be high enough that overall efficiencies could bring even more speed to the process, dissolving woody material nearly as fast as we can load it in (in a matter of days). I'd be curious to see how big a scale a refinery can get.

If our oil is replaced by this greener solution, we have a long future with ICEs, however, I don't it will be enough to slow the growth of EV and FC technologies too much. Most of the pushing factor for both of those is by governments.

I really see almost the vehicle pie being drawn out in thirds, EVs 33%, FCs33%, and ICEs 33%... If all three can get to at least carbon neutral in the next few decades, there shouldn't be much to worry about. I think these numbers support the lifestyle of most Americans, I think that 1/3 of Americans could easily charge vehicles at home and actually utilize a long range EV. Those in settings were you can't easily/reliably charge(apartments, rentals), would always have the gasoline option. If hydrogen from waste/renewables got to near cost parity on a GGE or even close to a parity on mileage performance, there is no reason to not use it.(if the former it could easily replace gasolineICEs.


ICEs will get cleaner burning with new EGR systems being developed, yes there will be particulate waste but even modern cars can 'clean' the air in certain cities (from other sources of pollution).

Also I have no qualms over using fossil fuels in the meantime to mature things like EVs and FCs. I don't care if it is coal, methane or solar, as long as it ultimately leads to increased efficiencies and better use of the energy from the source, with a goal in mind of eliminating most of the particulate emissions.

These things take time. Cars take about ten years to develop, new technologies like batteries take 10-20 years from inception to wide spread adoption.

I am excited for the future, I'd be interested in a FC. But I'd be equally happy with a PHEV with 40miles+ range. (could probably make my miles 70%+ EV and no need for a second car.)

Producers have found that clearing the biomass is GOOD for the land. Research was saying half the biomass could be taken, but what they are finding is they take most of it and plant a cover crop.

In some cases up to a foot deep stover accumulated on the land, reducing nitrogen returning to the soil and leaving the soil cold so they could not plant early in the spring. What we have now is farmers signing up to provide cellulose because it is better for the land and they make more money.

A bit too good to be true. Enzymes will eventually break down from contamination, such as the wrong acidity, or from restriction by other enzymes, which are themselves the product of solution contamination. High temperature pasteurization is still very much a part of alcohol fermentation as is still a high energy expense.

On the other hand, garbage can be a better feedstock for all of this than corn or woodchips. A plant in Cedar Rapids IA is trying to prove just that. There is enough wood pulp liquor in the area to do the job, which is laced with sulfuric acid and expensive to dispose of in landfill. Oils are a major impediment to cellulosic reclamation (pizza boxes?) but the multiplex approach of cleaning up the trash to get alcohol, specialty sugars, and construction grade aggregate sounds promising.

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