Alternative Pathway For Alcohol Biofuels

In an effort to advance biofuels, UCLA chemical engineers James C. Liao, Shota Atsumi, and Taizo Hanai have engineered Escherichia coli to produce C₃–C₅ alcohols from glucose using the bacteria's amino acid biosynthetic pathway (Nature 2008, 451, 86). These straight-chain and branched higher alcohols are more like the mix of compounds in gasoline and are expected to perform better as biofuels than ethanol. An existing industrial fermentation process generates 1-butanol using the bacterium Clostridium acetobutylicum. The researchers diverted the 2-keto acid intermediates from the amino acid synthesis into alcohol production, where they are first converted to aldehydes by 2-keto acid decarboxylases and then to alcohols by alcohol dehydrogenases. The biosynthetic pathway produces 1-butanol, isobutanol, and other alcohols, depending on the choice of the amino acid pathway, whereas the fermentation process produces only 1-butanol, Liao says. In addition, because the amino acid biosynthetic pathway is universal, the process can be transferred to other microorganisms, such as the yeast Saccharomyces cerevisiae.