n-hexane sensitivity of Escherichia coli due to low expression of imp/ostA encoding an 87 kDa minor protein associated with the outer membrane

Most Escherichia coli strains are resistant to n-hexane. E coli OST4251 is a n-hexane-sensitive strain that was constructed by transferring the n-hexane-sensitive phenotype from a n-hexanesensitive strain by P1 transcluction. OST4251 is resistant to diphenyl ether, which is less harmful than n-hexane to micro-organ isms. The genetic determinant responsible for this subtle difference in the solvent resistance is mapped at 1.2 min on the E coli chromosome. Nucleotide sequence analysis showed that IS2 and IS5 had integrated upstream of the implostA structural gene in OST4251. The integration of IS2 decreased the activity of the implostA promoter. A product of the gene was identified immunologically as an 87 kDa minor protein associated with the outer membrane. Upon transformation with plasmids containing the implostA gene, OST4251 produced a high level of the gene product in the membrane and acquired n-hexane resistance. Thus, the low level of promoter activity resulted in low Imp production and the n-hexane-sensitivity phenotype. It is likely that the gene product contributes to n-hexane resistance by reducing the influx of n-hexane.