In addition, Qureshi has teamed with Lars Angenent, an environmental engineer at Washington University, as well as other USDA-ARS researchers to improve the economics of the hydrolysis step. The idea is to replace the need for enzymes, which are often expensive, with a mixed culture of bacteria. “The real tenets of my lab involve studying nondefined mixed cultures and seeing what they can do,” Angenent explains. In the collaboration with Qureshi, Angenent will use microbes collected from the sludge of an anaerobic digester as well as microbes from sheep rumen to ferment pretreated corn fiber to butyric acid, a chemical found in rancid butter, parmesan cheese and vomit. The solution containing the acid will be sent to Qureshi’s lab where it will be fermented into butanol by his pure cultures of Clostridium.

The collaboration is in its infancy, financed by a $425,000 grant from the USDA. Currently, Angenent’s team is working to optimize the butyric acid production by tweaking conditions like pH and temperature. “We try to steer the community to produce one product over another,” he explains. Once conditions are right for the production of significant levels of butyric acid, Qureshi will take over.

Engineering Butanol-Fermenting Bugs
Whereas the approach spearheaded by Qureshi and Angenent involves optimizing butanol production by microbes that naturally produce it, a team of chemical and biomolecular engineers from the University of California, Los Angeles, recently reported a different course. In a recent issue of the journal Nature, the team led by James Liao, described how they genetically modified a well-known bacterium, Escherichia coli, to efficiently synthesize butanol, a molecule it doesn’t normally produce.

To do this, the team reasoned that they could divert some of the metabolites that E. coli uses to make amino acids, the building blocks of proteins, to a metabolic pathway that would result in the production of butanol. “Amino acid biosynthesis is very well studied in E. coli,” Liao explains. Using that knowledge, Liao’s team inserted two genes into the E. coli genome: one from a microbe involved in the production of cheese and one from a yeast. These genes express proteins that convert keto acids, components of the amino acid biosynthesis pathway, into butanol. In addition, by inhibiting the expression of other genes and making changes in certain proteins in the pathway, Liao was able to increase the efficiency of the process to a level high enough for industrial use. “By using these two tricks we could force the flux to the desired direction,” he says. “We were able to produce isobutanol very quickly and improved the titer in a few months.”

The technology is so promising that Gevo Inc., a biofuels startup based in Pasadena, Calif., recently announced that it acquired an exclusive license to commercialize Liao’s process. The company is currently scaling up the technology and deciding whether to go ahead with its own plans to build a butanol plant.

Liao, meanwhile, is working on converting cellulose waste materials into isobutanol as well as trying to implement the approach in other microbes. “We’re very excited about the promise of the project,” he says.

Jessica Ebert is a Biomass Magazine staff writer. Reach her at jebert@bbibiofuels.com or (701) 738-4962.

Sidebar Articles

<-- Previous Page	1   2
View Entire Article