Researchers from the UCLA Henry Samueli School of Engineering and Applied Science have genetically modified a cyanobacterium to consume carbon dioxide and produce the liquid fuel isobutanol, which has great potential as a gasoline alternative. The reaction is powered directly by energy from sunlight, through photosynthesis.
This method has two main advantages. First, it recycles carbon dioxide, reducing greenhouse gas emissions resulting from the burning of fossil fuels. Second, it uses solar energy to convert the carbon dioxide into a liquid fuel that can be used in the existing energy infrastructure - including in most automobiles.
"This new approach avoids the need for biomass deconstruction, either in the case of cellulosic biomass or algal biomass, which is a major economic barrier for biofuel production," said team leader James C. Liao, Chancellor's Professor of Chemical and Biomolecular Engineering. "Therefore, this is potentially much more efficient and less expensive than the current approach."
Using the cyanobacterium Synechoccus elongatus, the researchers genetically increased the quantity of the carbon dioxide–fixing enzyme RuBisCO. Then they spliced genes from other microorganisms to engineer a strain that intakes carbon dioxide and sunlight, and produces isobutyraldehyde gas. The low boiling point and high vapor pressure of the gas allows it to easily be stripped from the system.
The engineered bacteria can produce isobutanol directly, but the UCLA team says it is currently easier to use an existing and relatively inexpensive chemical catalysis process to convert isobutyraldehyde gas to isobutanol, as well as other useful petroleum-based products.
In addition to Liao, the team included Shota Atsumi, a former UCLA postdoctoral scholar now on the UC Davis faculty, and UCLA postdoctoral scholar Wendy Higashide.
An ideal place for this system would be next to existing power plants that emit carbon dioxide, according to the researchers, because it could potentially allow the greenhouse gas to be captured and directly recycled into liquid fuel.
"We are continuing to improve the rate and yield of the production," Liao said. "Other obstacles include the efficiency of light distribution and reduction of bioreactor cost. We are working on solutions to these problems."