Cornell University biological engineers have developed a method to make ethanol using an anaerobic microbe feeding on carbon monoxide, a common industrial waste gas.

“In order to make the microbes do our work, we had to figure out how they work, their metabolism,” says Ludmilla Aristilde, assistant professor in biological and environmental engineering.

Ethanol, an organic molecule, was created using an anaerobic microbe feeding on carbon monoxide, an inorganic waste gas. Image credit: DOE/NREL.To make biofuel from an inorganic waste product, the researchers learned that the bacterium Clostridium ljungdahlii responds thermodynamically—rather than genetically—in the process of tuning favorable enzymatic reactions. The scientists found that the microbe feasts on and then ferments carbon monoxide.

“When I eat food, I get energy out of my food by metabolizing my food,” Aristilde notes. “Microbes are the same. In terms of biostructure, the bacterial cells are starving for nutrients, so they are responding metabolically—which leads to a desired outcome, ethanol production.”

To get the microbe to ferment the carbon monoxide, the scientists “[bubbled] it in the growth medium solution, where the cells can feed on it," explains colleague Lars Angenent, professor of biological and environmental engineering, who collaborated on the project. "The microbial cells then turn it into ethanol, an organic molecule," Aristilde adds, "and carbon monoxide, an inorganic molecule, turns into something valuable we can use.”

Carbon monoxide gas emitted as a byproduct of heavy industries—such as the process for coking coal in the production of steel—could potentially be channeled to bioreactors that contain these bacterial cells, the researchers note.