Abstract
Isobutanol (IBT) can be used as a 100% replacement for gasoline in existing automobile engines, has >90% of the energy density of gasoline and is compatible with established fuel distribution infrastructure. The facultatively autotrophic bacterium Ralstonia eutropha can utilize H2 for energy and CO2 for carbon and is also employed in industrial processes that produce biodegradable plastics. Using a carefully designed production pathway, R. eutropha, a genetically tractable organism, can be modified to produce biofuels from autotrophic growth. Microbial production of IBT can be achieved by directing the flow of carbon through a synthetic production pathway involving the branched-chain amino acid biosynthesis pathway, a heterologously expressed ketoisovalerate decarboxylase, and a broad substrate specificity alcohol dehydrogenase. We discuss the motivations and the methods used to engineer R. eutropha to produce the liquid transportation fuel IBT from CO2, H2, and O2.