Specificity of reductive dehalogenation of substituted ortho- chlorophenols by Desulfitobacterium dehalogenans JW/IU-DC1

Abstract

Resting cells of Desulfitobacterium dehalogenans JW/IU-DC1 grown with pyruvate and 3-chloro-4-hydroxy-phenylacetate (3-Cl-4-OHPA) as the electron acceptor and inducer of dehalogenation reductively ortho-dehalogenate pentachlorophenol (PCP); tetrachlorophenols (TeCPs); the trichlorophenols 2,3,4-TCP, 2,3,6-TCP, and 2,4,6-TCP; the dichlorophenols 2,3-DCP, 2,4-DCP, and 2,6-DCP; 2,6-dichloro-4-R-phenols, where R is -H, -F, -Cl, -Br, -NO2, - CO2-, or -COOCH3; 2-chloro-4-R-phenols (2-Cl-4-RPs, where R is -H, -F, - Cl, -Br, -NO2, -CO2-, -CH2CO2-, or -COOCH3); and bromophenols (2-BrP, 2,6-DBrP, and 2-Br-4ClP). Monochlorophenols, the dichlorophenols 2,5-DCP, 3,4-DCP, and 3,5-DCP, the trichlorophenols 2,3,5-TCP, 2,4,5-TCP, and 3,4,5- TCP, and the fluorinated analog of 3-Cl-4-OHPA, 3-F-4-OHPA ('2-F-4- CH2CO2- P'), are not dehalogenated. A chlorine substituent in position 3 (meta), 4 (para), or 6 (second ortho) of the phenolic moiety facilitates ortho dehalogenation in position 2. Chlorine in the 5 (second meta) position has a negative effect on the dehalogenation rate or even prevents dechlorination in the 2 position. In general, 2,6-DCl-4-RPs are dechlorinated faster than the corresponding 2-Cl-4-RPs with the same substituent R in the 4 position. The highest dechlorination rate, however, was found for dechlorination of 2,3-DCP, with a maximal observed first-order rate constant of 19.4 h-1 g (dry weight) of biomass-1. There is no strong linear correlation between the logarithm of pseudo-first-order rate constants for the dehalogenation of 2,6-DCl-4-RPs and 2-Cl-4-RPs and electronic (Hammet σ(m)), hydrophobic (π), and stearic (E(s)) constants of the substituent R. The substrate specificity and induction pattern found for dehalogenation with the pure culture of D. dehalogenans and the original 2,4-DCP-enrichment, derived from a methanogenic sediment, were similar, suggesting that the conditions used led to only one type of dechlorinating organism.