Non-fermentative pathways for synthesis of branched-chain higher alcohols as biofuels

Global energy and environmental problems have stimulated increased efforts towards synthesizing biofuels from renewable resources(1-3). Compared to the traditional biofuel, ethanol, higher alcohols offer advantages as gasoline substitutes because of their higher energy density and lower hygroscopicity. In addition, branched- chain alcohols have higher octane numbers compared with their straight- chain counterparts. However, these alcohols cannot be synthesized economically using native organisms. Here we present a metabolic engineering approach using Escherichia coli to produce higher alcohols including isobutanol, 1-butanol, 2- methyl- 1- butanol, 3- methyl- 1- butanol and 2- phenylethanol from glucose, a renewable carbon source. This strategy uses the host's highly active amino acid biosynthetic pathway and diverts its 2- keto acid intermediates for alcohol synthesis. In particular, we have achieved high- yield, high- specificity production of isobutanol from glucose. The strategy enables the exploration of biofuels beyond those naturally accumulated to high quantities in microbial fermentation.