Researchers at UCLA led by Dr. James Liao have genetically engineered the common photosynthetic cyanobacterium—Synechococcus elongatus—efficiently to produce isobutyraldehyde and isobutanol directly from CO2. Isobutyraldehyde is a precursor for the synthesis of other chemicals, and isobutanol can be used as a gasoline substitute.
A paper on their work was published online in Nature Biotechnology 15 November. In December 2007, biofuels company Gevo acquired an exclusive license for a method developed by Dr. Liao for modifying the metabolic pathway of E.coli bacteria for the non-fermentative synthesis of higher alcohols including isobutanol, 1-butanol, 2-methyl-1-butanol, 3-methyl-1-butanol and 2-phenylethanol from glucose. Dr. Liao is on Gevo’s scientific advisory board. (Earlier post.)
The researchers modified S. elongatus by incorporating four genes from other bacteria into the structure. The new synthetic pathway begins with the photosynthetic conversion of CO2 to pyruvic acid; three further steps make isobutyraldehyde. Extracting the final product from the mix is a simple process.
The high vapor pressure of isobutyraldehyde allows in situ product recovery and reduces product toxicity. The engineered strain remained active for 8 days and produced isobutyraldehyde at a higher rate than those reported for ethanol, hydrogen or lipid production by cyanobacteria or algae.
These results underscore the promise of direct bioconversion of CO2 into fuels and chemicals, which bypasses the need for deconstruction of biomass.—Atsumi et al.
Shota Atsumi, Wendy Higashide & James C Liao (2009) Direct photosynthetic recycling of carbon dioxide to isobutyraldehyde.Nature Biotechnology doi: 10.1038/nbt.1586