Clean, green high performance biofuels from carbon dioxide

Could there come a time in which the carbon dioxide emitted from natural gas or coal-burning power plants that warms the atmosphere and exacerbates global climate change is harvested and used to produce clean, green and renewable liquid transportation fuels?

A pathway to that possibility has been opened by a team of researchers with the U.S. Department of Energy (DOE)'s Joint BioEnergy Institute (JBEI) who have engineered a microbe now being used to produce biodegradable plastic into a strain that can produce a high-performance advanced biofuel.

"We've shown that the bacterium Ralstonia eutropha growing with carbon dioxide and hydrogen gas is able to generate significant quantities of diesel-range methyl ketones," says Harry Beller, a JBEI microbiologist who led this research, which was funded through DOE's Advanced Research Projects Agency-Energy (ARPA-E) program. "This holds the promise of making carbon-neutral biofuels using non-photosynthetic, carbon-dioxide fixing bacteria as a less resource-intensive alternative to making these biofuels from cellulosic biomass."

Beller led a previous study in which genetic engineering was used to develop a strain of the bacterium Escherichia coli (E. coli) that made methyl ketone compounds from the glucose in cellulosic biomass. Methyl ketones are naturally occurring aliphatic compounds now used in fragrances and flavorings. Beller and his JBEI colleagues have demonstrated that methyl ketones also have high diesel fuel ratings (cetane numbers), making them strong candidates as advanced biofuels.

"We've shown that, with the same set of genetic modifications, R. eutropha and E. coli can make comparable amounts of methyl ketones, but R. eutropha is making the ketones from carbon dioxide while E. coli is making them from glucose," Beller says. "This shows that the methyl ketone pathway that we've designed is versatile and able to function well in bacterial hosts with substantially different metabolic lifestyles."