Stress tolerance of three opportunistic black yeasts

Many species of black yeasts can survive extremely harsh conditions and can quickly adapt to novel environments. These traits were proposed to have a role in the ability of some fungal species tocolonise indoor habitats inhospitable for majority of microorganisms, and to cause (opportunistic)infections in humans. In order to better understand the stress tolerance of black yeasts and thereby their opportunism, we focused our research on the three model black yeasts: the polyextremotolerant Au-reobasidium melanogenum and Exophiala dermatitidis, and the extremely halotolerant Hortaeawerneckii. These black yeasts are shown to thrive at temperatures, salinities, pH values and, H2O2 concentrations that inhibit growth of mesophilic species. Most importantly, unlike their close relatives they can not only grow, but also synthesize siderophores (E. dermatitidis) or degradeproteins (A. melanogenum) at 37 °C - traits that are crucial for pathogenesis in humans. These results support the hypothesis that the ability to cope with various environmental stresses is linked to the opportunistic behaviour of fungi. Therefore, better understanding of the connections between the stress-tolerant biology of black fungi and their ability to cause disease is needed, in particular due to their changing interactions with humans and their emerging pathogenicity.