Although it’s possible to incorporate all three genes in a single plant, says Sticklen, using three different varieties of corn, each carrying a different gene, will allow her to control the conversion of cellulose into sugars. Preliminary studies show that the enzymes are just as efficient as commercially available enzymes when combined at a ratio of 1:4:1, she says. The results suggest that mixing the three different plants using the same ratios will provide the best outcome.
“I think the strategy of compartmentalizing the enzymes in the vacuoles is terrific,” says Susan Leschine, a microbiologist at the University of Massachusetts Amherst. “The question I have is, do the enzymes work under conditions that are realistic?” For instance, different microbe species secrete their own cellulases that work synergistically to chip away at the cellulose fibers. It’s unclear, Leschine says, how well an enzyme taken from a microbe that lives in a hot spring will work with an enzyme drawn from a soil fungus. “These different enzymes may not be active under the same conditions,” she says.
Edenspace, which is currently developing Sticklen’s technology, expects to begin field trials of her genetically modified corn within the year, with the goal of commercializing the technology within the next three years, says Blaylock. The company is not alone in pursuing this strategy: Agrivida, an agricultural biotech company based in Medford, MA, is also genetically modifying corn to simplify the production of cellulosic ethanol.
“This really is a worthwhile path to follow,” says Michael Ladisch, professor of agricultural and biological engineering at Purdue University, in West Lafayette, IN. “However, at the end of the day, it’s more complicated than it seems.” The main obstacle is finding ways to ensure that the enzymes will survive the chemical and physical pretreatment needed to remove the lignin–the tough polymer in cell walls that provides plants with strength–from the cellulose fibers, says Ladisch, who is currently on leave from Purdue to serve as the chief technical officer at Mascoma, a biofuels company based in Brighton, MA.
One solution is to engineer the plants so that they require only a mild pretreatment. For instance, Sticklen is working on reducing the amount of lignin contained in corn, as well as modifying the molecular configuration of lignin, which would make it easier to break down. Although her work is currently focused on modifying corn, Sticklen says that the technology could eventually be transferred to other crops as well, such as switchgrass.