Molecular Approaches to Improve 1-Butanol Tolerance and Production in Escherichia coli

1-butanol toxicity is a major limiting factor for improving 1-butanol production in either a native 1-butanol producer (Clostridium) or non-native 1-butanol producing microbial hosts, especially Escherichia coli. Because of a low 1-butanol tolerance of 1 – 2% [v/v], the capability of these strains to produce 1-butanol with titers higher than the tolerance limits is severely reduced. While the 1-butanol tolerance of Clostridium strains has been intensively studied and improved via different approaches, concerns on enhancing the tolerance of E. coli just has been raised recently and efforts so far did not result in any significant improvement. These researches, moreover, did not show any linkage between the improved 1-butanol tolerance and production, since the host, E. coli, is incapable of producing 1-butanol naturally. Previously, we screened and identified a 1-butanol tolerant Artificial Transcription Factor (ATF) that increases the tolerance of E. coli in 1.5% [v/v] 1-butanol (published). On the other hand, we also selected rational approaches which were successfully applied to other hosts and evaluated their effects on E. coli tolerance. In this work, therefore, we study the impact of different groups of genes, including ATF, molecular chaperones, solvent efflux pump, etc. on both improving 1-butanol tolerance and production of E. coli by co-expressing them with the clostridial 1-butanol pathway. The result of this work would show a more practical evaluation on the significance of suggested approaches for improving 1-butanol tolerance in E. coli as a tool to increase the production capacity.