How to make 'green' fossil fuels

A University research team coaxes bacteria to do it

Until now, the least "green" thing on the planet has been fossil fuels. But that could change.

A University of Minnesota team is putting bacteria to work turning carbon dioxide—the primary greenhouse gas—into petroleum fuels, using energy from the sun.

This novel idea for making renewable fuels that you can put in your gas tank won the team a $2.2 million grant from the U.S. Department of Energy in October 2009.

Led by biochemistry professor Lawrence Wackett, the researchers are assembling a "co-culture" system in which two types of bacteria grow on opposite surfaces of a thin latex film. The bacteria on the upper surface will make glucose during photosynthesis. The glucose will then diffuse through the latex to the second bacteria, which will turn it into the building blocks of diesel and gasoline.

"We can get sugar made by photosynthesis (reactions driven by sunlight) turned into fuel precursors during the day," says Wackett. "And we can continue the process without sunlight during the night and use corn steep liquor—a waste product from milling corn during ethanol production—as a source of carbon."

The researchers have applied for a patent on the system and for the use of an enzyme called OleA in making fuel molecules in cells of the second bacteria.

OleA olé

The fuel that comes out of the gas pump is composed of chains of carbon atoms, each chemically bound to two or three hydrogen atoms. These hydrocarbons, as they're called, come in varying lengths; the most famous is octane, which has eight carbons.

The ultimate goal of the research is to get hydrocarbons from the second bacteria, called Shewanella. The work took a step forward when Wackett's then-graduate student Janice Frias discovered the exact mechanism by which OleA works. Briefly, OleA stitches two fatty acids together to form a ketone, which consists of two hydrocarbon chains with an oxygen atom at the juncture point.

To form usable hydrocarbons, the oxygen must be removed and the hydrocarbon chains chopped into the appropriate lengths—longer for diesel fuel, shorter for gasoline. Chemical engineering professors Lanny Schmidt and Aditya Bhan are refining catalytic technology they have developed to turn ketones made by Shewanella into diesel fuel.

Fossil fuel schematic - photo

A schematic of making renewable "fossil" fuels. Graphic by Ranja Sem.

When hydrocarbons come off this bio-based assembly line, the goal of obtaining "fossil" fuels made from sunlight, water, and—most importantly—carbon dioxide will have been realized.

Wowing the DOE

"Our central idea was the co-culture of two different kinds of bacteria," says Wackett. "The latex films are very thin, like paint without the pigment. You can spray the latex on any shape you want, the same as with solar cells."

The revolutionary nature of the project won over reviewers in the Department of Energy's Advanced Research Projects Agency-energy program, which awarded the $2.2 million grant.

"They told us they weren't looking for small steps forward—they wanted something completely new," says Wackett. The University's proposal was one of 37 chosen from a field of 3,700.

But the team still has its work cut out for it.

"A good biotech process today may make 100 million pounds of product a year," notes Wackett. "That's what an oil refinery puts out in a few days. Biotechnology has to scale up 100 times if it's going to rival a petroleum refinery, and that's not going to be easy."

Co-investigators with Wackett on the project are assistant microbiology professor Jeffrey Gralnick, Bhan, Schmidt, and Marc von Keitz, chief technical officer of BioCee Inc. On April 1, Frias, along with Wackett, research associate professor Jack Richman, and undergraduate Jasmine Erickson, published the OleA work in the Journal of Biological Chemistry.