Isobutanol has a higher carbon content than ethanol, therefore making its energy properties closer to gasoline. Currently, isobutanol is used as a precursor for commodity chemicals including isobutyl acetate. Atsumi et al [1] synthesized isobutanol via synthetic biology. The origin of the enzymes required to synthesize isobutanol were from a variety of microorganisms including Lactococcus lactis and Saccharomyces cerevisiae. In addition to expressing foreign enzymes, the host, E. coli, was modified to direct metabolism toward isobutanol production. The interesting feature of this pathway to synthesize isobutanol is that it employs amino acid biosynthesis to generate the essential precursor. This allows the microbe to produce the alcohol in the presence of oxygen. In fact, semi-aerobic conditions increased yields. This approach has been applied to generate several other alcohols, such as 2-phenylethanol and 2-methyl-1-butanol. The pathways for these interesting alcohols have not yet been optimized.

[1] Atsumi, S., Hanai, T., Liao, J.C., 2008, Nature 431, 86-89.