Fluorophenols and 3-fluorobenzoate in phenol-degrading methanogenic cultures

Abstract

3-Fluorobenzoate and all three isomers of fluorophenol were used as analogues and inhibitors of phenol degradation in a methanogenic consortium. 3-Fluorobenzoate was not transformed by phenol-degrading cultures, but it facilitated the detection of the formation of 4-hydroxybenzoate and benzoate from phenol. The effects of the fluorophenols depended on their concentration in the cultures. When added at 0.90 mM, all fluorophenols prevented phenol transformation. At concentrations of 0.45 to 1.8 mM, 2-fluorophenol was transformed to 3-fluoro-4-hydroxybenzoate which accumulated in the medium. When both 2-fluorophenol and phenol were added to cultures at concentrations of 1 mM each, 3-fluoro-4-hydroxybenzoate, 4-hydroxybenzoate, 3-fluorobenzoate and benzoate were detected. 4-Fluorophenol was never transformed, and when it was present at ≦0.22 mM, it had no effect on phenol degradation. At concentrations ≦0.09 mM, 2-fluorophenol was mineralized by the phenol-degrading cultures to methane, carbon dioxide, and fluoride. The release of fluoride was also observed from 3-fluorophenol when it was initially present at ≦0.09 mM. These results support the proposed pathway for phenol degradation involving an initial para-carboxylation to 4-hydroxybenzoate followed by dehydroxylation to benzoate and further metabolism to carbon dioxide and methane. They also demonstrate defluorination of 2- and 3-fluorophenols under methanogenic conditions.