Involvement of AcrAB and TolC Efflux Pump System with Organic Solvent Tolerance of Escherichia coli
Kei KOBAYASHI, Norihiko TSUKAGOSHI, Hiroyuki ASAKO, Harushi NAKAJIMA, and Rikizo AONO
Department of Bioengineering, Faculty of Bioscience and Biotechnology, Tokyo Institute of Technology, Nagatsuta 4259, Midori-ku, Yokohama 226, Japan
Most hydrophobic organic solvents can be toxic to microbes. However, certain bacteria grow in the presence of harmful organic solvents. It is expected that bacteria have some defensive systems for organic solvents, and these systems are enable cells to grow in the presence of such solvents. We have shown that soxS, marA or robA gene is responsible for elevating the tolerance of Escherichia coli K-12. These genes encode DNA-binding proteins that are transcriptional activators, indicating that these proteins induce some genes which directly defend E. coli cells from organic solvent toxicity.
We certified that levels of AcrA and TolC proteins are increased in E. coli of which organic solvent tolerance was elevated by spontaneous mutation, P1 transduction, or transformation with one of the three genes. These proteins are components of multiple effiux pump complex (AcrAB system). To investigate involvement of acrAB with organic solvent tolerance, acrAB genes were isolated from E. coli. We obtained an octane (log Pow 4.9)-sensitive E. coli strain with mutation in acrAB loci. Organic solvent tolerance level of this strain was improved by transformation with the cloned acrAB genes to diphenyl ether (log Pow 4.2)- or n- hexane (log Pow 3.9)-tolerance. In this acrAB defective strain, soxS, marA or robA gene was not effective to improve the tolerance level. Thus, the expression of acrAB increases organic solvent tolerance of E. coli and organic solvent tolerant system induced by soxS, marA or robA depends on acrAB-manner.
