Phenoloxidase activity of dark pigmented yeast-like fungi of Aureobasidium and Hormonema genera

Abstract

The phenoloxidase activity as a possible taxonomic feature of Aureobasidium and Hormonema strains was studied by qualitative method on agar media (potato-dextrose agar, Czapek’s medium and water agar), where 0.05 % of α-naphthol, guaiacol, and D-tyrosine were added, respectively. Tyrosinase and laccase activities of 13 tested strains of dark pigmented yeast-like fungi Aureobasidium pullulans , Hormonema dematioides , Hormonema sp. and Rhinocladiella sp. were intracellular, which cannot be detected outside of the cells. These activities didn’t depend on the radioactivity level of habitats of isolated strains. The laccase presence for the studied A. pullulans strains was not detected on Czapek’s medium and water agar, the tyrosinase reaction was absent or very low. Hormonema sp., H. dematioides and Rhinocladiella sp. strains detected significant level of laccase activity, the tyrosinase activity was medium or high. The quantitative determination of laccase and tyrosinase activities was carried out by using 11 substrates (catechol, L-DOPA, pyrogallol, p-cresol, D-tyrosine, p-phenylenediamine, guaiacol, 2,6-DMOP, phloroglucinol, resorcinol and hydroquinone) at pH 4.0 and 7.0. The tyrosinase and laccase activities were absent in culture filtrates of studied strains and were observed only in cell extracts. The tyrosinase and laccase activities of Hormonema sp., H . dematioides and Rhinocladiella sp. strains were absent or significantly lower at pH 7.0 than at pH 4.0. The tyrosinase activity prevails for A. pullulans and laccase activity – for Hormonema strains, that can be used as an important additional criterion for identification of fungi of Aureobasidium and Hormonema genera.