Utilization of low molecular weight aromatic compounds by heterobasidiomycetous yeasts: taxonomic implications.

The utilization of low molecular weight aromatic compounds implies the operation of complex metabolic pathways. In order to investigate the taxonomic relevance of this property among heterobasidiomycetous yeasts, both at the species level and at higher taxonomic ranks, the capacity to assimilate twenty such compounds was tested in a total of 332 strains representing approximately 200 species. The substrates most frequently utilized were protocatechuic, caffeic, and p-hydroxybenzoic acids, whereas cinnamic, sinapic, and syringic acids and guaiacol were never assimilated. The assimilation of the majority of the aromatic compounds investigated correlated with the utilization of protocatechuic acid. Among the Urediniomycetes, the members of the Sporidiales and those of the Naohidea-Rhodotorula minuta clade showed a good ability to utilize aromatic compounds, whereas the members of the Agaricostilbum-Kondoa group were more heterogeneous, in agreement with the four subclades known. Among the Tremellomycetidae, the members of the Cystofilobasidium and Tremella clades showed a reduced or null ability to utilize aromatic compounds. In contrast, the members of the Trichosporon clade were able to utilize phenol and similar substrates, and the representatives of the Filobasidium clade assimilated various aromatic compounds, including those requiring more complex catabolic routes. Assimilation tests using, as sole carbon and energy sources, low molecular weight aromatic compounds appear to be potentially useful in taxonomic studies of basidiomycetous yeasts. In those species in which a considerable number of strains was investigated, variable assimilation patterns were frequently observed. The possibility that such discrepant results indicate an incorrect species delimitation is discussed.