Glutathione metabolism and dimorphism in Aureobasidium pullulans

Abstract

Yeast⟷mycelium morphological transitions of Aureobasidium pullulans are influenced by numerous environmental factors. In general, changes in the glutathione (GSH) metabolism of dimorphic fungi may lead to alterations in the reduced thiol status of the cells that are hypothesised to initialise morphological transitions. In accordance with this hypothesis, the specific GSH levels found in A. pullulans yeast cells were always significantly higher than those in mycelia. On the other hand, there was no significant difference between the GSH/GSSG redox status of the cells with either yeast or mycelial morphology. The cascade of events leading to morphological transitions was therefore unlikely to proceed via redox modulation of protein thiols. Although there were morphology-dependent differences in the specific activities of some GSH metabolic enzymes, e.g. glutathione reductase (GR),γ-glutamyltranspeptidase (γGT), glucose-6-phosphate dehydrogenase (G6PD), they were not satisfactory to explain the observed alterations in the intracellular GSH levels. It is noteworthy that very similar specific γGT and G6PD activities were found in cells separated from mixed morphology cultures independently of the actual cell morphology. On the other hand, the specific γGT and G6PD activities of A. pullulans cells sharing the same morphology but separated from pure and mixed morphology cultures showed marked differences.