Aromatic Degradation in Yeast Rhodotorula rubra

Aromatic degradation by two yeast strains of Rhodotorula (R.) rubra was examined. Separation and identification of phenol and protocatechuic acid (PCA) metabolites were carried out using high performance liquid chromatography (HPLC) and gas chromatography/mass spectrometry (GC/MS). For HPLC analysis of β -ketoadipic acid, 2,4-dinitrophenylhydrazone derivative was prepared. For GC/MS analysis, metabolites in the cultured broth were extracted with ethyl acetate and trimethylsilylated by N-o-bis(trimethylsilyl)acetoamide. Based on HPLC and GC/MS analyses, phenol metabolites were identified as catechol, eis, cis-muconic acid, muconolactone, β -ketoadipate enol-lactone and β -ketoadipic acid. β -Ketoadipic acid was also found in the PCA metabolites by crude cell-free extract. From the results obtained in this study, a metabolic sequence for aromatic degradation is proposed. Phenol may be hydroxylated to form catechol prior to ring cleavage, and catechol may be further oxidized to eis, cis-muconic acid, muconolactone, β -ketoadipate enol-lactone and β -ketoadipic acid. Catechol branch as well as protocatechuate branch in β -ketoadipate pathway may exist in R. rubra.