Tom Mitchell, a plant pathologist at the Ohio Agricultural Research and Development Center is tapping into his knowledge of fungal biology and genomics to improve the process by which lignocellulosic biomass -- things like crop residue, fast-growing trees and perennial grasses such as switchgrass -- are turned into ethanol.
Producing biofuels from lignocellulosic biomass (instead of corn) holds great promise for both economic and environmental reasons, since it doesn't take away grain from food and feed production and involves crops that grow well on marginal land.
But unlike corn, lignocellulosic feedstocks contain high amounts of lignin -- hard tissue that makes plants stronger, but which need to be destroyed during a pre-treatment process to better access the cellulose inside. (Cellulose is mixed with water and enzymes, fermented and distilled into ethanol.) The high cost of this pre-treatment process has limited the commercial viability of making biofuels from non-food sources. But it leads to other issues, too.
"Currently, the industry standard is to pre-treat lignocellulosic biomass with heat or harsh substances, such as acids, which not only makes the process expensive but also generates chemical waste," Mitchell explains. "Pre-treatment also affects the microbial fermentation process that helps produce fuel, due to the erosive nature of the chemicals used."
Mitchell has devised a different way to deal with lignin -- one that would eliminate the need for pre-treatment or require only a light pre-treatment, allowing the cellulosic ethanol industry to be more competitive and have less of an environmental impact.
"Regardless of the feedstock being used to produce lignocellulosic ethanol, the main tough nut to crack is the same: how to get rid of the lignin," Mitchell says. "My approach is to develop plant varieties that have very low lignin content to begin with. In other words, let the plants break down their own lignin."
How can this be accomplished? Mitchell is experimenting with two types of genes, known as laccase and ligninase, whose natural role is to chew up lignin in plants. Many organisms can make these genes, but fungi that have evolved to attack plants have the most of them, since they are very good at degrading plant tissue.
"We looked at the genomes of fungi currently available, some 500 of them, and checked to see which ones had these genes," Mitchell says. "The two top fungi were Stagonospora nodorum and Magnaporthe oryzae, which is not surprising considering their ability to attack and destroy crops."
Mitchell then chose the top seven candidate genes, took them out of the fungi and -- with collaboration from fellow Ohio State plant pathologist Guo Liang Wang -- put them into Arabidopsis, a lab model plant. The result: 50-60% less lignin in the stems of modified plants.
Next in the process, Mitchell says, is to refine the model, find the best gene to use, and later try it on agricultural crops: rice (whose straw can be used to produce ethanol) and switchgrass.
With over 180 million tons available annually on a global basis, lignocellulosic material represents the most abundant and sustainable resource for biofuel production.