title: Acute toxicity of (chloro-)catechols and (chloro-)catechol-copper combinations in Escherichia coli corresponds to their membrane toxicity in vitro.
abstract: (Chloro-)catechols are toxic for bacteria and higher organisms, but the mode of action is not yet clearly understood. We have compared the acute toxicity of different chlorinated catechols to Escherichia coli with membrane toxic effects, namely narcosis and uncoupling that we have determined in an in vitro assay. In vitro membrane toxicity was quantified by measuring the accelerated decay of the membrane potential of chromatophores isolated from Rhodobacter sphaeroides. Both acute and membrane toxicity increased with increasing degree of chlorination. Analysis of dose-response curves, pH dependence, and estimated membrane concentrations gave a consistent picture of the mechanisms of membrane toxicity: At pH 7, the higher-chlorinated catechols acted as uncouplers of oxidative and photophosphorylation, and the lower-chlorinated catechols and catechol acted as narcotics. In the case of 3,5-dichlorocatechol and 4-monochlorocatechol at pH 8.8, both mechanisms appeared to contribute to the overall toxicity. Copper exhibited a diverging effect on the toxicity of catechols and of (chloro-)catechols to E. coli. Whereas the presence of copper increased the toxicity of catechol and 4-monochlorocatechol, the toxicity of 3,5-dichlorocatechol, 3,4,5-trichlorocatechol, and tetrachlorocatechol decreased. Again, the results obtained with in vitro assays agreed with the acute toxicity observed in E. coli: The presence of copper accelerated decay of the membrane potential of catechol and 4-monochlorocatechol; however, the effect was reversed by copper in experiments with 3,5-dichlorocatechol, 3,4,5-trichlorocatechol, and tetrachlorocatechol. We have proposed a mechanistic model to explain the diverging effects of copper on the uncoupling activities of the different catechols.
authors.affiliation: Swiss Federal Institute for Environmental Science and Technology, Zürich, Switzerland.
authors.forename: N
authors.initials: N
authors.lastname: Schweigert
authors.forename: R W
authors.initials: RW
authors.lastname: Hunziker
authors.forename: B I
authors.initials: BI
authors.lastname: Escher
authors.forename: R I
authors.initials: RI
authors.lastname: Eggen
mesh_terms: D002396:Catechols / Q000633:toxicity*; D002462:Cell Membrane / Q000187:drug effects; D003300:Copper / Q000633:toxicity*; D004926:Escherichia coli / Q000187:drug effects*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects
chemical_list: D002396:Catechols; D003300:Copper