Study of the methanogenic degradation of phenol via carboxylation to benzoate

Abstract

An anaerobic bacterial consortium carboxylating phenol to benzoate by cometabolism in the presence of proteose peptone under methanogenic conditions was studied. Yeast extract or a mixture of tryptophan and lysine could replace proteose peptone without affecting the carboxylating activity, whereas glucose, glycerol, pyruvate, volatile fatty acids, and sodium bicarbonate could not. The carboxylating microorganism could not be obtained pure from the phenol culture supplemented with tryptophan and lysine; six different morphological types of microorganisms were able to grow in this medium. The results obtained with potential intermediates of benzoate degradation given as substrates to the consortium suggest that benzoate is transformed to 1-cyclohexene carboxylate and to heptanoate. Part of 1-cyclohexene carboxylate was transformed to an apparent dead-end product identified as cyclohexane carboxylate. Key words: phenol, carboxylation, benzoate, methanogenic conditions.