Original Papers

Archives of Microbiology

, Volume 152, Issue 6, pp 594-599

Anaerobic degradation of phenol via carboxylation to 4-hydroxybenzoate: in vitro study of isotope exchange between 14CO2 and 4-hydroxybenzoate

  • Andreas TschechAffiliated withAngewandte Mikrobiologie, Universität Ulm
  • , Georg FuchsAffiliated withAngewandte Mikrobiologie, Universität Ulm

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Extracts of denitrifying bacteria grown anaerobically with phenol and nitrate catalyzed an isotope exchange between 14CO2 and the carboxyl group of 4-hydroxybenzoate. This exchange reaction is ascribed to a novel enzyme, phenol carboxylase, initiating the anaerobic degradation of phenol by para-carboxylation to 4-hydroxybenzoate. Some properties of this enzyme were determined by studying the isotope exchange reaction. Phenol carboxylase was rapidly inactivated by oxygen; strictly anoxic conditions were essential for preserving enzyme activity. The exchange reaction specifically was catalyzed with 4-hydroxybenzoate but not with other aromatic acids. Only the carboxyl group was exchanged; [U-14C]phenol was not exchanged with the aromatic ring of 4-hydroxybenzoate. Exchange activity depended on Mn2+ and inorganic phosphate and was not inhibited by avidin. Ortho-phosphate could not be substituted by organic phosphates nor by inorganic anions; arsenate had no effect. The pH optimum was between pH 6.5–7.0. The specific activity was 100 nmol 14CO2 exchange · min-1 · mg-1 protein. Phenol grown cells contained 4-hydroxybenzoyl CoA synthetase activity (40 nmol · min-1 · mg-1 protein). The possible role of phenol carboxylase and 4-hydroxybenzoyl CoA synthetase in anaerobic phenol metabolism is discussed.

Key words

Anaerobic degradation Aromatic compounds Phenol 4-Hydroxybenzoate Carboxylation Pseudomonas sp.