J. Basic Microbiol. 41 (2001) 1, 131– 137 ( 1 Department of Microbiology and Biotechnology, Faculty of Science, University of Debrecen, P.O. Box 63., H-4010 Debrecen, Hungary and 2 Department of General Microbiology, Institute of Molecular Biology, University of Copenhagen, Sølvgade 83H., DK-1307 Copenhagen K, Denmark) Glutathione metabolism and dimorphism in Aureobasidium pullulans CLAUDIA WÜRTZ JÜRGENSEN 1, 2,* , NICKLAS RAUN JACOBSEN 1, 2,* , TAMÁS EMRI 1 , SUSANNE HAVN ERIKSEN 2 and ISTVÁN PÓCSI 1 (Received 21 December 2000/Accepted 06 February 2001) Yeastlmycelium 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 mor- phological transitions. In accordance with this hypothesis, the specific GSH levels found in A. pullu- lans 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 myce- lial 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 differ- ences in the specific activities of some GSH metabolic enzymes, e.g. glutathione reductase (GR), J-glutamyltranspeptidase (J GT), glucose-6-phosphate dehydrogenase (G6PD), they were not satis- factory to explain the observed alterations in the intracellular GSH levels. It is noteworthy that very similar specific J GT and G6PD activities were found in cells separated from mixed morphology cul- tures independently of the actual cell morphology. On the other hand, the specific J GT and G6PD ac- tivities of A. pullulans cells sharing the same morphology but separated from pure and mixed mor- phology cultures showed marked differences. Yeastlmycelium (YlM) transitions. The term dimorphism is used to describe the abil- ity of fungi to grow in more than one distinct morphological form (CANNON et al. 1994). A wide range of fungi from all classes of the Eumycota exhibits dimorphism in response to environmental conditions, and dimorphism is quite common in many important plant and human pathogenic fungi (DEACON 1997). It is noteworthy that the pathogenicity of these fungi is generally limited to only one of the morphological forms (ORLOWSKI 1994). Morphological transition is provoked by a large constellation of environmental parame- ters in dimorphic fungi (ORLOWSKI 1994). The environmental factors to which particular fungi respond are diverse, but the environmental stimuli often include changes in growth temperature, pH, nutritional factors, CO 2 tension, redox potential, etc. For many fungal systems the environmental conditions that induce morphogenesis have been characterised, however, little is known about the cellular signalling pathways and regulatory factors con- trolling the differentiation process (DEACON 1997). Studies on the opportunistic human pathogenic fungus Candida albicans have provided us with experimental data on the possible involvement of glutathione (J -L-glutamyl-L- cysteinyl-glycine, GSH 1 ) in the regulation of YlM conversions (THOMAS et al. 1991, * C. W. Jürgensen and N. R. Jacobsen contributed equally to the elaboration of this project 1 Abbreviations: GPx, glutathione peroxidase; GR, glutathione reductase; GSH, glutathione; GSSG, glutathione disulphide; GST, glutathione S-transferase; J GT, J -glutamyltranspeptidase; G6PD, glucose-6-phosphate dehydrogenase; SD, standard deviation; SOD, superoxide dismutase