Findings on Butanol Toxicity May Enable Cheaper Biofuel Production

by Michael Miller (University of Cincinnati/Phys.Org) One limitation of producing biofuel is that the alcohol created by fermentation is toxic to the microbes that produce it. Now scientists are closer to overcoming this obstacle.

Researchers from the University of Cincinnati and the U.S. Department of Energy's Oak Ridge National Laboratory have achieved a breakthrough in understanding the vulnerability of microbes to the alcohols they produce during fermentation of plant biomass.

With the national lab's neutron scattering and simulation equipment, the team analyzed fermentation of the biofuel butanol, an energy-packed alcohol that also can be used as a solvent or chemical feedstock.

Butanol is toxic to the very microorganisms that produce it. This toxicity limits the amount of butanol that can be generated during fermentation, presenting a challenge to bio-based production, said Jonathan Nickels, an associate professor of chemical and environmental engineering in UC's College of Engineering and Applied Science.

"The primary location of toxicity is in the membrane," Nickels said. "Ultimately, the solvent thins it out and makes it softer and less stable. Ultimately, you get holes in the membrane. When this happens, the cell loses the ability to generate energy."

Researchers found that butanol tends to accumulate unevenly around the membrane, causing some regions to thin more than others. This could be responsible for the cell stress and less efficient fermentation.

Lead author Luoxi Tan, a doctoral graduate of UC's College of Engineering and Applied Science, is continuing this collaboration as a postdoctoral researcher at the national laboratory. He said researchers will now look to see if they can make biofuel more efficiently by stabilizing the membranes of the cells in the biomass.

"(The findings) provide us with new targets to reduce the influence of these fermentation products," Tan said.

Researchers investigated the processes occurring during fermentation using neutron scattering experiments that allow for non-destructive testing of the membrane, letting scientists see the structures and arrangements of molecules.

"Neutrons give you the ability to probe the interior of the membrane to help determine how the butanol is distributed," said Hugh O'Neill, director of the Center for Structural Molecular Biology at Oak Ridge.

Researchers used supercomputers to perform molecular dynamics simulations to examine how atoms and molecules move and interact over time. Nickels said these tools allowed researchers to see what was happening to the structure of a cell's membrane at the molecular level.

"The findings have very relevant and meaningful long-term implications," Nickels said. "We want to make biofuels more efficient, which would have significant economic outcomes." READ MORE