Fungal diseases such asStagonosporanodorumandMagnaporthe oryzaecause significant losses to wheat and rice crops throughout the world. Now, anOhio State University scientist is trying to use these bad fungi for good --taking some of their genes to breed bioenergy crops that could make ethanolproduction cheaper and moreefficient.
A plantpathologist with the university's Ohio Agricultural Research and DevelopmentCenter (OARDC), Tom Mitchell is tapping into his knowledge of fungal biologyandgenomics to improve the process by which lignocellulosic biomass -- thingslike crop residue, fast-growing trees and perennial grasses such asswitchgrass -- are turned intoethanol.
Producingbiofuels from lignocellulosic biomass (instead of corn) holds great promise forboth economic and environmental reasons, since it doesn't take away grain fromfood andfeed production and involves crops that grow well on marginal land.
But unlike corn,lignocellulosic feedstocks contain high amounts of lignin -- hard tissue thatmakes plants stronger, but which need to be destroyed during a pre-treatmentprocess tobetter access the cellulose inside. (Cellulose is mixed with waterand enzymes, fermented and distilled into ethanol.) The high cost of thispre-treatment process has limited thecommercial viability of making biofuelsfrom non-food sources. But it leads toother issues, too.
"Currently, theindustry standard is to pre-treat lignocellulosic biomass with heat or harshsubstances, such as acids, which not only makes the process expensive but alsogenerateschemical waste," Mitchell explained. "Pre-treatment also affects themicrobial fermentation process that helps produce fuel, due to the erosivenature of the chemicals used."
Mitchell hasdevised a different way to deal with lignin -- one that would eliminate the needfor pre-treatment or require only a light pre-treatment, allowing thecellulosic ethanolindustry to be more competitive and have less of anenvironmental impact.
"Regardless ofthe feedstock being used to produce lignocellulosic ethanol, the main tough nutto crack is the same: how to get rid of the lignin," Mitchell explained. "Myapproach isto develop plant varieties that have very low lignin content tobegin with. In other words, let the plants break down their own lignin."
How can this beaccomplished? Mitchell is experimenting with two types of genes, known aslaccase and ligninase, whose natural role is to chew up lignin in plants. Manyorganisms can make these genes, but fungi that have evolved to attack plantshave the most of them, since they are very good at degrading plant tissue.
"We looked at thegenomes of fungi currently available, some 500 of them, and checked to seewhich ones had these genes," Mitchell said. "The two top fungi wereStagonosporanodorumandMagnaporthe oryzae, which is notsurprising considering their ability to attack and destroy crops."
Mitchell then chosethe top seven candidate genes, took them out of the fungi and -- withcollaboration from fellow Ohio State plant pathologist Guo Liang Wang -- putthem intoArabidopsis, a lab model plant. The result: 50-60 percent less ligninin the stems of modified plants.
Next in theprocess, Mitchell said, is to refine the model, find the best gene to use, andlater try it on agricultural crops: rice (whose straw can be used to produceethanol) andswitchgrass.
With over 180million tons available annually on a global basis, lignocellulosic material representsthe most abundant and sustainable resource for biofuel production.