Novel scheme for biosynthesis of aryl metabolites from L-phenylalanine in the fungus Bjerkandera adusta

Aryl metabolite biosynthesis was studied in the white rot fungus Bjerkander a adusta cultivated in a liquid medium supplemented with L-phenglalanine. A romatic compounds were analyzed by gas chromatography-mass spectrometry fol lowing addition of labelled precursors (C-14- and C-13-labelled L-phenylala nine), which did not interfere with fungal metabolism. The major aromatic c ompounds identified were benzyl alcohol, benzaldehyde (bitter almond aroma) , and benzoic acid. Hydroxy- and methoxybenzylic compounds (alcohols, aldeh ydes, and acids) were also found in fungal cultures. Intracellular enzymati c activities (phenylalanine ammonia lyase, aryl-alcohol oxidase, aryl-alcoh ol dehydrogenase, aryl-aldehyde dehydrogenase, lignin peroxidase) and extra cellular enzymatic activities (aryl-alcohol oxidase, lignin peroxidase), as well as aromatic compounds, were detected in B. adusta cultures. Metabolit e formation required de novo protein biosynthesis. Our results show that L- phenylalanine was deaminated to trans-cinnamic acid by a phenylalanine ammo nia lyase and trans-cinnamic acid was in turn converted to aromatic acids ( phenylpyruvic, phenylacetic, mandelic, and benzoylformic acids); benzaldehy de was a metabolic intermediate. These acids were transformed into benzalde hyde, benzyl alcohol, and benzoic acid. Our findings support the hypothesis that all of these compounds are intermediates in the biosynthetic pathway from L-phenylalanine to argl metabolites. Additionally, trans-cinnamic acid can also be transformed via beta-oxidation to benzoic acid. This was confi rmed by the presence of acetophenone as a beta-oxidation degradation interm ediate. To our knowledge, this is the first time that a beta-oxidation sequ ence leading to benzoic acid synthesis has been found in a white rot fungus . A novel metabolic scheme for biosynthesis of aryl metabolites from L-phen ylalanine is proposed.