Process Development for the Production of Isobutanol

All of the above-mentioned examples for fermentative isobutanol production were performed in simple flasks or bottles. However, the development of feasible production processes is challenging since not only common upscale problems arise, but also the cytotoxicity of higher alcohols is a striking problem for the transfer into the industrial scale. 

In analogy to the process with C. glutamicum Iso7, a two-phase fermentation process was developed with PDHC-deficient B. subtilis n-,05 yielding 74 mM isobutanol (5.5 g/L). In this case, the yield obtained [0.47 mole per mole (0.19 g/g) Li et al 2012b] was about the same (or even slightly higher) when compared to that observed in flask batch fermentations (Table 12.4). 

Synthesis gas, a mixture of mainly CO, CO2, and H2, has been used in chemical industry as feedstock and can be generated by gasification of coal and oil but also from biomass, municipal waste, or by recycling of used plastics (Kopke et al., 2010). Isobutanol production from synthesis gas has so far not been reported. However, Kopke et al. (2010) engineered Clostridium ljungdahlii, which is naturally able to use synthesis gas as carbon and energy source, for the production of 1-butanol by implementation of the CoA-dependent 1-butanol synthesis pathway from Clostridium acetobutylicum. The final titer of about 0.5 mM 1-butanol was rather low however, this approach demonstrated the feasibility to produce fuels and chemicals from synthesis gas. 

Just recently, Huo et al. (2011, 2012) engineered E. coli for the protein-based higher alcohol production. This was achieved by directed evolution using chemical 

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