Uncoupler Resistance in Escherichia coli: the Role of Cellular Respiration

Department of Biochemistry, University of Oxford, South Parks Road, Oxford 0X1 3QU, UK Department of Biochemistry and Agricultural Biochemistry, University College of Wales, Aberystwyth, Dyfed SY23 3DD, UK ABSTRACT Summary: Bioenergetic properties of a mutant strain of Escherichia coli K12 designated TUV, which is resistant to the protonophoric uncoupling agent 4,5,6,7-tetrachloro-2-trifluoromethylbenzimid-azole (TTFB) have been compared with those of its non-resistant parent, E. coli K12 Doc-S. Strain TUV grew and respired some 20-30% faster than strain Doc-S, and was cross-resistant to carbonylcyanide p -(trifluoromethoxy)phenylhydrazone and triphenyltin, but not to 2,4-dinitrophenol. Phosphorus nuclear magnetic resonance demonstrated the TTFB-mediated collapse of the transmembrane pH gradient at identical rates in starved cells of both strains, indicating that uncoupler access and function were unimpaired in the mutant under these conditions. Strain TUV displayed enhanced uncoupler resistance and maintained intracellular pH and ATP levels only when respiring. On the other hand, strain TUV also showed increased resistance to novobiocin, implying that its outer wall permeability had been lowered. We suggest that the active resistance of strain TUV results from the exclusion of uncoupler by the interaction of inner and outer membrane components in a manner modulated by the degree of cellular energization. Present address: Mount Sinai Medical Center, Department of Biochemistry, Box 1020, 1 Gustave L. Levy Place, New York, NY 10029, USA. Present address: Department of Biochemistry, University of Birmingham, PO Box 363, Birmingham B15 2TT, UK.