Reversible Conversion of 4-Hydroxybenzoate and Phenol by Clostridium hydroxybenzoicum

Reversible conversion of 4-hydroxybenzoate and phenol and their analogs was observed in whole-cell suspensions and cell extracts of Clostridium hydroxybenzoicum grown with 4-hydroxybenzoate and 3,4-dihydroxybenzoate. Assuming that bicarbonate is the cosubstrate, the equilibrium constants calculated for the reactions 4-hydroxybenzoate^- + H₂O phenol + HCO₃^- and 3,4-dihydroxybenzoate^- + H₂O catechol + HCO₃^- were 11.4 (± 0.5) and 5.05 (± 0.25), respectively. In a phenol-adapted sediment slurry, 4-hydroxybenzoate and 3,4-dihydroxybenzoate were decarboxylated to phenol and to catechol, respectively, as intermediates without a lag time.