Researchers from the University of York (United Kingdom) and Aix-Marseille Université (France) have discovered a new family of enzymes capable of degrading hard-to-digest biomass into its constituent sugars.

Finding a way to break down hard-to-digest or recalcitrant materials, such as plant stems, wood chips, cardboard waste or insect/crustacean shells, into their constituent sugars to allow them to be fermented into bioethanol is regarded as the 'Holy Grail' of biofuel research. Fuels made from these lignocellulosic sources are known as second generation biofuels.

The research team reported in the journal Nature Chemical Biology the detailed biochemical characterization of a newly discovered family of lytic polysaccharide monooxygenase (LPMO) enzyme from Aspergillus oryzae, a fungus widely used in fermentation industries. LPMOs are a recently discovered class of enzymes capable of oxidizing recalcitrant polysaccharides. The recently reported enzyme belongs to the third LPMO family of enzymes discovered.

The recent discovery is considered as a significant step in the development of second generation biofuels.

The results of field trials with genetically modified (GM) poplar trees in Belgium and France have shown improved conversion of wood biomass into sugars for making bio-ethanol. The GM poplars produce low levels of cinnamoyl-CoA reductase (CCR) enzyme to suppress the formation of lignin polymer which is a tough barrier in biomass processing.

The study, published as an open access paper in Proceedings of the National Academy of Sciences (PNAS), also found that strong down-regulation of CCR affected biomass yield. The research team from Belgium, France and the United States concluded that the strategy of down-regulating the CCR may work to improve biomass processing if such yield penalty can be overcome.

The study showed that the suppression of the lignin biosynthesis in some trees is stronger than others, indicated by varying intensity of red coloration of the wood beneath the bark. The branches with the highest red coloration produce 160 percent more ethanol. On the average, the ethanol yield per gram of modified wood is 20 percent higher than that of non-modified wood.

The negative effect of CCR down-regulation points to the fact that the modified poplar trees appear to grow less rapid than non-modified trees. As the scientists begin to understand what causes the growth retardation, they plan to start to work on poplars that grow normally, but still have a stable suppression of the lignin production. In a new field trial in Belgium in 2014, trees that have been developed to suppress another enzyme through modern technique, for a more uniform lignin supression will be tested.

Researchers at the National Renewable Energy Laboratory (NREL) of the U.S. Department of Energy have found that an enzyme produced by a bacterium that thrives in hot springs possesses remarkable catalytic properties which enable it to digest cellulose almost twice as fast as the leading commercial cellulase enzyme.

NREL researchers have tested and characterized the CelA enzyme secreted by Caldicellulosiruptor bescii, a bacterium first found in the Valley of Geysers on the Kamchatka Peninsula in Russia in 1990. They found that CelA produced more fermentable sugars than Cel7A, the most potent cellulase enzyme in leading commercial enzyme mixtures, under industry standard test for cellulose degradation. They found that CelA not only can digest cellulose, but it also creates cavities in the material, which leads to greater synergy with more conventional cellulases, resulting in higher sugar release.

The NREL researchers who reported their finding in the journal Science described CelA as "an amazingly complex enzyme", which combines two catalytic domains with three binding modules." The dual catalytic domains working in concert are most likely responsible for fast degradation of cellulose.

NREL scientists also found that CelA can attack xylose, which means that the amount of enzymes in commercial cocktails for removing xylose could be further lowered, translating to lower costs. The enzyme with its remarkable cellulose digesting mechanism promises to bring down the cost of making lignocellulosic biofuels or fuels made from hard-to-digest biomass sources.