Gut feeling over a cellulosic biofuels breakthrough

Newly discovered enzyme complexes in the digestive tracts of herbivores could hold promise for the future of sustainable fuels, according to new research from the University of California – Santa Barbara.

Assistant engineering professor Michelle O’Malley from UCSB and 20 other scientists have collaborated on a study describing a new complex of enzymes discovered in herbivore gut fungi. According to their paper detailing the findings, published in the journal Nature Microbiology, the enzymes could have applications in chemical and medical production, as well as biofuels.

The fungi discovered by O’Malley and colleagues have ‘unusual and desirable’ characteristics, according to a statement from UCSB, including the ability to transform lignocellulose from plants into sugars.

In the fungus Anaeromyces robustus, individual enzymes are joined together and arranged as a large protein mass or scaffold. According to O’Malley, the result is that the structure “kind of glues the enzymes together for maximum impact to break down the non-food parts of plants.” This is markedly different to how plants are broken down in industrial processes, such as cellulosic bioethanol production, which relies on free-floating enzyme mixtures to break down biomass.

"From our preliminary evidence, the enzymes we're studying have the potential to be better for industrial use than the ones being used now," said Sean Gilmore, a Ph.D. student in O'Malley's lab and a co-author on the paper.

O’Malley explained that in current cellulosic ethanol production: “You need to have several different 'flavors' of enzymes to get the end product you want. Each enzyme has a different job. Those enzymes are added as a kind of cocktail mixture, and they run into each other randomly to create the necessary reactants. What's different about the structures we've identified is that the enzymes are tethered, so the reactions and their products are moved along an assembly line, expanding their activity for maximum impact rather than happening by luck."

The report is the first to describe cellulosome structures in fungi, and to note that the fungi have "stolen" some of the parts from bacteria, through a process called "horizontal gene transfer.”

O’Malley and colleagues’ findings improve understanding on how cellulose is converted into sugar. "From a biotech perspective, that gives us a recipe to try to build similar complexes that could then be engineered to more efficiently break down widely available crop waste," she noted. "It's the whole idea of value-added production: you take something that people would just burn before and then use these enzyme machines to extract sugar from it, which is fed to microbes, which can then make things for us. Further, knowledge of these fungal complexes could be applied to engineer completely synthetic assembly lines to build, for instance, novel chemicals and pharmaceuticals."