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Patent Picks: Enzymatic Breakdown Of Biomass

A look at recent patenting activity in enzymatic breakdown of biomass, brought to you by C&EN and CAS

November 20, 2014 | A version of this story appeared in Volume 92, Issue 47



Two enzyme systems are better than one

Cellulosomes and free cellulase enzymes work together to hydrolyze cellulosic biomass better than either one alone.
Credit: Courtesy of Michael Resch/NREL
Cellulosomes and free cellulase enzymes work together to hydrolyze cellulosic biomass.

Turning biomass into valuable biofuels and biobased chemicals requires breaking down the plant material’s complex polysaccharides into simpler sugars. Heat and acid hydrolysis can do the job, but energy requirements and yield concerns have driven scientists to consider alternatives, particularly cellulose-busting enzymes isolated from fungi and other organisms that chew up biomass. These so-called cellulases typically are more selective and operate under milder conditions than thermochemical treatments. Patenting activity in Chemical Abstracts Service databases reveal that scientists are pushing to make cellulases a commercially viable alternative to thermochemical methods by boosting the enzymes’ catalytic activity, efficiency, and yields. Three such patents are highlighted here.


No-fuss isolation of cellulases

A cartoon depicting cellulases anchored to a silica surface by a tether consisting of mercaptotrimethoxysilane, gold nanoparticles, and an amino acid.
Credit: C&EN
Cellulases are anchored to a silica surface by a tether consisting of mercaptotrimethoxysilane, gold nanoparticles, and an amino acid.

Not all biomass-busting organisms go about their work the same way: Some use cocktails of individual cellulase enzymes. Others rely on large multienzyme complexes called cellulosomes. Michael Resch of the Department of Energy’s National Renewable Energy Laboratory and coworkers recently explored how these different systems catalyze cellulose hydrolysis (US 20140030769). They report that free cellulases break down the outermost layer of cellulose first and then work their way down, whereas cellulosomes separate individual cellulose microfibrils from one another before chewing them up. On the basis of these systems’ complementary mechanisms, the researchers suggest that using a combination might further accelerate the hydrolysis of cellulose. To prove it, they combined cellulosomes produced by the cellulose-degrading bacterium Clostridium thermocellum and CTec2, a free cellulase sold by Novozymes, in a ratio of 50:50 and used the mixture to hydrolyze a commercial microcrystalline cellulose powder. The mixture exhibits significantly higher catalytic activity than the total activity of both systems when used alone, “hinting at a means for faster and more efficient conversion of biomass, which would lead to lower costs for biomass-derived renewable fuels,” the authors say.


Immobilizing cellulases for easy reuse

Extracting and isolating free cellulases or cellulosomes from biomass-degrading organisms can be costly and time-consuming. Hoping to reduce or even eliminate this tedious process while maintaining high cellulolytic activity, Ely Morag and coworkers from Israel-based Designer Energy have come up with an easy way of turning biomass-degrading organisms into pellets that can hydrolyze cellulose (WO 2014108900). The researchers grow cellulosome-producing microorganisms in the presence of cellulosic biomass and then collect the insoluble components as crude pellets. They show that the pellets can hydrolyze cellulose without the need for purification steps to isolate enzymes or separate the cells and other materials, such as residual unhydrolyzed biomass, from the pellets. The pellets’ cellulose hydrolysis activity is dramatically higher than that of commercial enzyme cocktails. And they work under a wider range of conditions than the organisms from which they were isolated.

Patent Picks is a collaborative effort by C&EN and CAS. This feature reports on trends CAS scientists observe from patents in CAS databases. Patents now generate more than 70% of the new substances appearing in the literature.

To reduce the cost of enzymatic cellulose hydrolysis, scientists have immobilized the enzymes on a solid support so that they can be recovered easily and reused. Current strategies for doing so include sol‑gel encapsulation, absorption, cross-linking, and chemical covalent bonding. But it’s challenging to keep enzymes immobilized in these ways working efficiently over the long haul. Chean-Yeh Cheng and Kuo-Chung Chang from Chung Yuan Christian University, in Taiwan, discovered a better way: They coat silica with mercaptotri­methoxysilane; use this chemical handle to sequentially add gold nanoparticles, an amino acid, and a peptide-bond coupling agent; and then covalently attach a cellulase to the modified silica (US 20140120600). The authors claim the preparation conditions are mild and the method is reproducible. More important, the immobilized cellulase can be recovered and reused many times while maintaining high activities. These features allowed the researchers to design a continuous cellulose hydrolysis process that boasts higher efficiency than the conventional batch reaction.


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