SPECIFICITY OF REDUCTIVE DEHALOGENATION OF SUBSTITUTED ORTHO-CHLOROPHENOLS BY DESULFITOBACTERIUM DEHALOGENANS JW IU-DC1/

Resting cells of Desulfitobacterium dehalogenans JW/IU-DC1 grown with pyruvate and 3-chloro-4-hydroxyphenylacetate (3-Cl-4-ORPA) as the elec tron acceptor and inducer of dehalogenation reductively ortho-dehaloge nate pentachlorophenol (PCP); tetrachlorophenols (TeCPs); the trichlor ophenols 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, -NO2, -CO2-, or -COOCH3; 2-chloro-4-R-phenols (2-Cl-4-RPs, wher e R is -H, -F, -Cl, -Br, -NO2, -CO2-, -CH2CO2-, or -COOCH3); and bromo phenols (2-BrP, 2,6-DBrP, and 2-Br-4ClP). Monochlorophenols, the dichl orophenols 2,5-DCP, 3,4-DCP, and 3,5-DCP, the trichlorophenols 2,3,5-T CP, 2,4,5-TCP, and 3,4,5-TCP, and the fluorinated analog of 3-Cl-4-OHP A, 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. Chlori ne in the 5 (second meta) position has a negative effect on the dehalo genation rate or even prevents dechlorination in the 2 position. In ge neral, 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 d echlorination 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 dehalogena tion of 2,6-DCl-4-RPs and 2-Cl-4-RPs and electronic (Hammet sigma(m)), hydrophobic (pi), and stearic (E(s)) constants of the substituent R. The substrate specificity and induction pattern found for dehalogenati on with the pure culture of D. dehalogenans and the original 2,4-DCP-e nrichment, derived from a methanogenic sediment, were similar, suggest ing that the conditions used led to only one type of dechlorinating or ganism.