Current knowledge on isobutanol production with Escherichia coli, Bacillus subtilis and Corynebacterium glutamicum

Abstract

Due to steadily rising crude oil prices great efforts have been made to develop designer bugs for the fermentative production of higher alcohols, such as 2-methyl-1-butanol, 3-methyl-1-butanol and 2-Methyl-1-propanol (isobutanol), which all possess quality characteristics comparable to traditional oil based fuels. The common metabolic engineering approach uses the last two steps of the Ehrlich pathway, catalyzed by 2-ketoacid decarboxylase and an alcohol dehydrogenase converting the branched chain 2-ketoacids of L-isoleucine, L-leucine, and L-valine into the respective alcohols. This strategy was successfully used to engineer well suited and industrially employed bacteria, such as Escherichia coli, Bacillus subtilis and Corynebacterium glutamicum for the production of higher alcohols. Among these alcohols, isobutanol is currently the most promising one regarding final titer and yield. This article summarizes the current knowledge and achievements on isobutanol production with E. coli, B. subtilis and C. glutamicum regarding the metabolic engineering approaches and process conditions.

Figure 1

Enzymes of the biosynthetic pathway of L-valine and the synthetic pathway from 2-ketoisovalerate to isobutanol. ADH, alcohol dehydrogenase; AHAIR, acetohydroxy isomeroreductase; AHAS, acetohydroxyacid synthase; DHAD, dihydroxyacid dehydratase; KIVD, 2-ketoacid decarboxylase.

Figure 2

Proposed transhydrogenase-like cycle in C. glutamicum. MalE, malic enzyme; MDH, malate dehydrogenase; PCx, pyruvate carboxylase; PEP, phosphoenolpyruvate; PEPCx, PEP carboxylase; PK, pyruvate kinase.