IN efforts to use corn stalks, grass and other non-food plants to make biofuels, scientists described the discovery of candidate enzymes in fungi that thrive in the feces and intestinal tracts of horses.
Dr. Michelle A. O'Malley of the University of California-Santa Barbara and colleagues reported on these enzymes at the recent National Meeting & Exposition of the American Chemical Society.
O'Malley explained that cellulose is the raw material for making biofuels from non-food plant materials. However, cellulose is sealed away inside a tough network of lignin within the cell walls of plants.
To produce biofuels from these materials, lignin must be removed through an expensive pretreatment process. Then, a collection of enzymes breaks down cellulose into sugars. Finally, those sugars become food for microbes to ferment into alcohol for fuel, ingredients for plastics and other materials.
"Nature has made it very difficult and expensive to access the cellulose in plants. Additionally, we need to find the best enzyme mixture to convert that cellulose into sugar," O'Malley said. "We have discovered a fungus from the digestive tract of a horse that addresses both issues: It thrives on lignin-rich plants and converts these materials into sugars for the animal. It is a potential treasure trove of enzymes for solving this problem and reducing the cost of biofuels."
Scientists seeking such enzymes have often looked to the digestive tracts of large herbivores like cows and horses, which can digest lignin-rich grasses.
In the past, the focus has been mainly on enzymes in bacteria rather than fungi, which include yeasts and molds. The goal: Take the genes that produce such enzymes from gut fungi, and genetically engineer them into yeasts, which are already used in industrial processes.
O'Malley explained that several genes from gut fungi are unique compared to bacteria since the fungi grow invasively into plant material. Also, they secrete powerful enzyme complexes that work together to break down cellulose. Until now, fungi have largely been ignored in the search for new biofuel enzymes because it is difficult to isolate and grow them to study their enzymes.
O'Malley's research group at the University of California-Santa Barbara collaborated with researchers at the Broad Institute of the Massachusetts Institute of Technology and Harvard University.
They worked with a gut fungus isolated from horse feces and identified all of the genetic material that the fungus uses to manufacture enzymes and other proteins. The team is now sifting through that genetic material to identify the most active enzyme and working on methods to transfer the genetic machinery for the enzyme's production into the yeast currently used in industrial processes.