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.

Efficient Turnover of Chlorocatechols Is Essential for Growth of Ralstonia eutropha JMP134(pJP4) in 3-Chlorobenzoic Acid

“…As the wild-type strain is able to grow in 3-CB while it accumulates significant amounts of 2-chloromuconate, the possible toxic effect of this metabolite, if there is any, should not be strong enough to prevent growth in 3-CB. In contrast, toxicity of chlorocatechols for bacterial cells has been reported for several organisms (1,10,13,35,36), including R. eutropha (this study). Therefore, the presence of adequate levels of chlorocatechol-consuming enzyme activities should be essential for growth in 3-CB (Fig.…”

“…Therefore, we assumed that lower enzyme activities of deriv- atives of strain JMP222 harboring chromosomal copies of the tfd gene clusters could produce an accumulation of toxic intermediates. Chlorocatechols are compounds that affect bacterial growth (35,36). We hypothesized that chlorocatechols accumulate and produce toxic effects in R. eutropha, and this possibility was studied.…”

Induction of enzymes of 2,4-dichlorophenoxyacetate degradation in Burkholderia cepacia 2a and toxicity of metabolic intermediates

“…Succinate could possibly be dispensed with by reducing the oxygen supply. Benndorf et al (2006) found that 3,5-DCC was much more toxic towards P. putida KT2440 than 2,4-D or 2,4-DCP, and actively uncoupled oxidative phosphorylation, as has also been found in E. coli (Schweigert et al 2001).…”

Derivatives of Resveratrol: Potential Agents in Prevention and Treatment of Cardiovascular Disease

“…It has been pointed out that the protonated phenolic group is not a particularly good ligand for metal cations, but once deprotonated, an oxygen center is generated that possesses a high charge density. Although the pKa 1 value of catechol is 9.25 [74], the hydroxyl proton could dissociate at much lower pH values, e.g., 5.0-8.0, in the presence of Cu(II) [75]. Therefore, 3,4-DHS should dissociate to form a phenoxide, which chelates Cu(II) as a bidentate ligand and undergoes intramolecular electron transfer to form ortho-hydroxyphenoxyl radicals.…”