Improvement of Organic Solvent Tolerance Level of Escherichia coli by Overexpression of Stress-Responsible Genes
Rikizo AONO*
Department of Bioengineering, Faculty of Bioscience and Biotechnology, Tokyo Institute of Technology, Nagatsuta 4259, Midori-ku, Yokohama 226, Japan
Water-immiscible organic solvents can be toxic to microorganisms. Each microorganism shows the intrinsic level of organic solvent tolerance. The tolerance levels differed among strains of Escherichia coli, suggesting that the organic solvent tolerance level is determined genetically. Probably, bacteria have some defensive systems for organic solvents, and these systems are enable cells to grow in the presence of such solvents. Magnitude of defence ability by the system is likely strain- specific.
We have studied genetically organic solvent tolerance of E. coli K-12. Previously, we constructed several mutants from E. coli, of which organic solvent tolerance levels were improved. Recently, it was shown that the mutants were defective in marR gene encoding a repressor protein for mar operon. This operon is responsible for multiple antibiotic resistance of E. coli. We have evidenced that soxS, marA and robA genes cloned by the shotgun method improve organic solvent tolerance levels of several strains of E. coli. Gene soxS is responsible for superoxide resistance. These genes code commonly for DNA-binding proteins that are transcriptional activators belonging to the AraC subfamily with helix-turn-helix motif and are responsible for various environmental stress factors.
