"We are in a host that is easier to work with, and we have a chance to make it even better," Chang said. "We are reaching yields where, if we could make two to three times more, we could probably start to think about designing an industrial process around it."
"We were excited to break through the multi-gram barrier, which was challenging," she added.
Among the reasons for engineering microbes to make fuels is to avoid the toxic byproducts of conventional fossil fuel refining, and, ultimately, to replace fossil fuels with more environmentally friendly biofuels produced from plants. If microbes can be engineered to turn nearly every carbon atom they eat into recoverable fuel, they could help the world achieve a more carbon-neutral transportation fuel that would reduce the pollution now contributing to global climate change. Chang is a member of UC Berkeley's year-old Center for Green Chemistry.
The basic steps evolved by Clostridium to make butanol involve five enzymes that convert a common molecule, acetyl-CoA, into n-butanol. Other researchers who have engineered yeast or E. coli to produce n-butanol have taken the entire enzyme pathway and transplanted it into these microbes. However, n-butanol is not produced rapidly in these systems because the native enzymes can work in reverse to convert butanol back into its starting precursors.
Chang avoided this problem by searching for organisms that have similar enzymes, but that work so slowly in reverse that little n-butanol is lost through a backward reaction.
"Depending on the specific way an enzyme catalyzes a reaction, you can force it in the forward direction by reducing the speed at which the back reaction occurs," she said. "If the back reaction is slow enough, then the transformation becomes effectively irreversible, allowing us to accumulate more of the final product."
Chang found two new enzyme versions in published sequ
|Contact: Robert Sanders|
University of California - Berkeley