Direct photosynthetic recycling of carbon dioxide to isobutyraldehyde

Abstract

The feasibility of recycling CO2 to biofuels in photosynthetic organisms will depend on advances in productivity and product-purification efficiency. Atsumi et al. improve the direct conversion of CO2 by engineering Synechococcus elongatus to produce isobutyraldehyde, which can be easily recovered from the production medium. Global climate change has stimulated efforts to reduce CO2 emissions. One approach to addressing this problem is to recycle CO2 directly into fuels or chemicals using photosynthesis. Here we genetically engineered Synechococcus elongatus PCC7942 to produce isobutyraldehyde and isobutanol directly from CO2 and increased productivity by overexpression of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco). Isobutyraldehyde is a precursor for the synthesis of other chemicals, and isobutanol can be used as a gasoline substitute. The high vapor pressure of isobutyraldehyde allows in situ product recovery and reduces product toxicity. The engineered strain remained active for 8 d and produced isobutyraldehyde at a higher rate than those reported for ethanol1, hydrogen2 or lipid3 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.