Functional Genomic Study of Exogenous n-Butanol Stress in Escherichia Coli

n-Butanol has been proposed as an alternative biofuel to ethanol, and both Escherichia coli and Saccharomyces cerevisiae have been engineered to produce it. Unfortunately, n-butanol is more toxic than ethanol to these organisms. To understand the basis for its toxicity, cell wide studies were conducted at the transcript, protein and metabolite levels to obtain a global view of the n-butanol stress response. Analysis of the data indicates that n-butanol stress has components common to other stress responses including perturbation of respiratory functions (nuo, cyo operons), oxidative stress (sodA, sodC, yqhD), heat shock and cell envelope stress (rpoE, clpB, htpG, cpxR, cpxP, degP), and metabolite transport and biosynthesis (malE, opp operon). Florescence assays revealed a large increase in reactive oxygen species during n-butanol stress, confirming observations from the microarray and proteomics data. Strains mutant in several genes whose products changed most dramatically during butanol stress were examined for increased sensitivity to n-butanol. Results from these analyses allow identification of key genes that were recruited to alleviate oxidative stress, protein misfolding and other causes of growth defect. Chassis engineering based on these cues may be required in a high titer, butanol-producing host.