The conversion by a methanogenic consortium of phenol into phenylalanine, with benzoic and phenylpropionic acid as intermediates, was investigated. When (sup14)C-labelled phenol was fed to the consortium, the radioactivity was mostly transferred into methane and CO(inf2), but 4% of the radioactivity was found in the water fraction after extraction of the culture medium with an organic solvent. Utilization of labelled compounds and analysis by gas chromatography coupled with mass spectrometry revealed that a fraction of the benzoic acid produced was transformed into 3-phenylpropionic acid. When fully (sup13)C-labelled acetic acid was fed to the consortium, the labels were incorporated at the 1 and 2 positions of 3-phenylpropionic acid. When deuterium-labelled 3-phenylpropionic acid was fed to the consortium, part of the phenylalanine of the biomass was labelled. These metabolic transformations are reversible, since deuterium-labelled phenylalanine generated labelled 3-phenylpropionic acid. Cinnamic acid was also transformed into 3-phenylpropionic acid.
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