White D G, Goldman J D, Demple B, Levy S B
Center for Adaptation Genetics and Drug Resistance and Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts 02111, USA.
J Bacteriol. 1997 Oct;179(19):6122-6. doi: 10.1128/jb.179.19.6122-6126.1997.
Escherichia coli K-12 strains are normally tolerant to n-hexane and susceptible to cyclohexane. Constitutive expression of marA of the multiple antibiotic resistance (mar) locus or of the soxS or robA gene product produced tolerance to cyclohexane. Inactivation of the mar locus or the robA locus, but not the soxRS locus, increased organic solvent susceptibility in the wild type and Mar mutants (to both n-hexane and cyclohexane). The organic solvent hypersusceptibility is a newly described phenotype for a robA-inactivated strain. Multicopy expression of mar, soxS, or robA induced cyclohexane tolerance in strains with a deleted or inactivated chromosomal mar, soxRS, or robA locus; thus, each transcriptional activator acts independently of the others. However, in a strain with 39 kb of chromosomal DNA, including the mar locus, deleted, only the multicopy complete mar locus, consisting of its two operons, produced cyclohexane tolerance. Deletion of acrAB from either wild-type E. coli K-12 or a Mar mutant resulted in loss of tolerance to both n-hexane and cyclohexane. Organic solvent tolerance mediated by mar, soxS, or robA was not restored in strains with acrAB deleted. These findings strongly suggest that active efflux specified by the acrAB locus is linked to intrinsic organic solvent tolerance and to tolerance mediated by the marA, soxS, or robA gene product in E. coli.
大肠杆菌K-12菌株通常对正己烷耐受，而对环己烷敏感。多重抗生素抗性（mar）位点的marA、soxS或robA基因产物的组成型表达产生了对环己烷的耐受性。mar位点或robA位点（而非soxRS位点）的失活增加了野生型和Mar突变体对有机溶剂的敏感性（对正己烷和环己烷均如此）。有机溶剂超敏感性是robA失活菌株新描述的一种表型。mar、soxS或robA的多拷贝表达在染色体mar、soxRS或robA位点缺失或失活的菌株中诱导了对环己烷的耐受性；因此，每个转录激活因子独立发挥作用。然而，在一个缺失了包括mar位点在内的39 kb染色体DNA的菌株中，只有由其两个操纵子组成的多拷贝完整mar位点产生了对环己烷的耐受性。从野生型大肠杆菌K-12或Mar突变体中删除acrAB会导致对正己烷和环己烷的耐受性丧失。在acrAB缺失的菌株中，由mar、soxS或robA介导的有机溶剂耐受性未恢复。这些发现强烈表明，acrAB位点所指定的主动外排与大肠杆菌的固有有机溶剂耐受性以及由marA、soxS或robA基因产物介导的耐受性相关联。
