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

Abstract

'Higher' alcohols offer advantages over ethanol as biofuels thanks to their higher energy densities and lower hygroscopicities, and 'branched' alcohols have higher octane numbers than their straight-chain counterparts. But these other alcohols cannot be synthesized economically using native microorganisms. Now an Escherichia coli strain has been re-engineered to produce higher alcohols (including isobutanol, 1-butanol and 2-phenylethanol) from glucose, a renewable carbon source. The strategy involves diverting intermediates from the amino acid biosynthetic pathway to generate the desired alcohol and may facilitate large-scale production of biofuels by microbial fermentation. A metabolic engineering approach is used to re-engineer Escherichia coli so that it could produce higher alcohols from glucose, a renewable energy source. The strategy involves diverting intermediates in the amino acid biosynthetic pathway to synthesize the desired alcohol and may facilitate the large-scale production of biofuels via microbial fermentation. Global energy and environmental problems have stimulated increased efforts towards synthesizing biofuels from renewable resources1,2,3. 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.