The Department of Energy announced yesterday that a team of researchers at the Department’s BioEnergy Science Center have successfully produced isobutanol, a fuel that is similar to gasoline, directly from cellulosic material like corn stalks or switchgrass. “This is a perfect example of the promising opportunity we have to create a major new industry – one based on bio-material such as wheat and rice straw, corn stover, lumber wastes, and plants specifically developed for bio-fuel production that require far less fertilizer and other energy inputs,” said Energy Secretary Steven Chu.
The researchers, led by James Liao of the University of California at Los Angeles, were faced with the challenge of chemically dismantling a plant’s cellulose, which has natural defenses against such degradation. To make such bioprocessing possible, Liao and postdoctoral researcher Wendy Higashide of UCLA and Yongchao Li and Yunfeng Yang of Oak Ridge National Laboratory had to develop a strain of Clostridium cellulolyticum, a native cellulose-degrading microbe, that could synthesize isobutanol directly from cellulose. The resulting process, called consolidated bioprocessing, saves costly steps in producing biofuels.
“In nature, no microorganisms have been identified that possess all of the characteristics necessary for the ideal consolidated bioprocessing strain, so we knew we had to genetically engineer a strain for this purpose,” Li said. While there were many possible microbial candidates, the research team ultimately chose Clostridium cellulolyticum, which was originally isolated from decayed grass. The researchers noted that their strategy exploits the host’s natural cellulolytic activity and the amino acid biosynthetic pathway and diverts its intermediates to produce higher alcohol than ethanol.
So why the focus on isobutanol? For starters, it is a better candidate for gasoline replacement than ethanol because its energy density, octane value, and volatility is much closer to gasoline. “Unlike ethanol, isobutanol can be blended at any ratio with gasoline and should eliminate the need for dedicated infrastructure in tanks or vehicles,” said Liao. “Plus, it may be possible to use isobutanol directly in current engines without modification.”
Don’t expect to see it at your local gas station any time soon, though. The study was a proof of concept study. Nevertheless, it sets the stage for studies that will probably involve genetic manipulation of other consolidated bioprocessing microorganisms. If you want to read more, the paper is titled “Metabolic Engineering of Clostridium Cellulolyticum for Isobutanol Production from Cellulose,” and is available online at http://aem.asm.org/.