Sunday, May 4, 2008
2-27

Butanol Tolerance in a Selection of Microorganisms

Eric P. Knoshaug and Min Zhang. National Renewable Energy Laboratory, 1617 Cole Blvd MS 3323, Golden, CO 80401

As an alternative liquid fuel, butanol offers distinct advantages because of its high energy content, miscibility with gasoline, octane-improving power, and low volatility. With the increasing price of oil, there is renewed interest in producing butanol biologically. Butanol can be produced from anaerobic bacterial (Clostridia) fermentations in a process that also produces acetone and ethanol (“ABE” fermentation) but suffers from low yield and productivity. Due to sensitivity to butanol and extremely complex regulatory pathways involved in switching from acidogenesis to solventogenesis in Clostridia, it has been difficult to make significant progress in engineering highly productive strains. An alternative strategy would be to establish the butanol production pathway in an alternative host lacking these complex regulatory pathways. However, an important consideration in selecting a host for butanol production is butanol tolerance. We conducted a screening of a variety of microorganisms known to be easily engineered to sample the level of butanol tolerance presently available in typical laboratory organisms. Currently this information is lacking in the literature but is crucial for the future engineering of highly productive butanol producing microorganisms. We present butanol tolerance data in the form of growth rates for strains of Escherichia coli, Saccharomyces cerevisiae, Zymomonas mobilis, Lactobacillus sp., Clostridium sp., and Non-Saccharomyces yeast species. The results show that varying levels of tolerance to butanol exist in wild type organisms.

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