Stress-tolerant fungi that can thrive under various environmental extremes are highly desirable for their application to biological control, as an alternative to chemicals for pest management. However, in fungi, the mechanisms of stress tolerance might also have roles in mammal opportunism. We tested five species with high biocontrol potential in agriculture (Aureobasidium pullulans, Debayomyces hansenii, Meyerozyma guilliermondii, Metschnikowia fructicola, Rhodotorula mucilaginosa) and two species recognized as emerging opportunistic human pathogens (Exophiala dermatitidis, Aureobasidium melanogenum) for growth under oligotrophic conditions and at 37 °C, and for tolerance to oxidative stress, formation of biofilms, production of hydrolytic enzymes and siderophores, and use of hydrocarbons as sole carbon source. The results show large overlap between traits desirable for biocontrol and traits linked to opportunism (growth under oligotrophic conditions, production of siderophores at 37 °C, high oxidative stress tolerance, and specific enzyme activities). Based on existing knowledge and these data, we suggest that oligotrophism and thermotolerance together with siderophore production at 37 °C, urease activity, melanization, and biofilm production are the main traits that increase the potential for fungi to cause opportunistic infections in mammals. These traits should be carefully considered when assessing safety of potential biocontrol agents.
COBISS.SI-ID: 4966223
Numerous agents of infections in humans and other mammals are found among fungi that are able to survive extreme environmental conditions and to quickly adapt to novel habitats. Nevertheless, the relationship between opportunistic potential and polyextremotolerance was not yet studied systematically in fungi. Here, the link between polyextremotolerance and opportunistic pathogenicity is shown in a kingdom-wide phylogenetic analysis as a statistically significant co-occurrence of extremotolerance (e.g. osmotolerance and psychrotolerance) and opportunism at the level of fungal orders. In addition to extremotolerance, fungal opportunists share another characteristic—an apparent lack of specialised virulence traits. This is illustrated by a comparative genomic analysis of 20 dothideomycetous and eurotiomycetous black fungi including fungi from the genus Aureobasidium.
COBISS.SI-ID: 34039769
Halotolerant yeasts were known for a long time exclusively as contaminants of food preserved with high concentrations of either salt or sugar. Their presence in natural thalassohaline hypersaline environments was unknown until 2000, when they were first reported to be active inhabitants of man-made solar salterns in Slovenia. Since then, they have been described in different salterns and salt lakes on three continents, on the surface of halophytic plants, in salt mines and cold as well as temperate saline lakes. Additionally they have been isolated from athalassohaline environments, such as MgCl2 saturated waters of the Dead sea and bitterns in the salterns, introducing a new category of extremophiles – chaophilic yeasts. The chapter uncovers yeasts mycobiota that inhabits these natural hypersaline environments and in more details presents the three fungi, namely Aureobasidum pullulans, Debaryomyces hansenii and Hortaea werneckii, which have now been isolated globally from natural hypersaline environments, and represent suitable model organisms for the study of halotolerance in eukaryotes.
COBISS.SI-ID: 4511055
The fungal genus Wallemia of the order Wallemiales (Wallemiomycotina, Basidiomycota) comprises the most xerotolerant, xerophilic and also halophilic species worldwide. Wallemia spp. are found in various osmotically challenged environments, such as dry, salted, or highly sugared foods, dry feed, hypersaline waters of solar salterns, salt crystals, indoor and outdoor air, and agriculture aerosols. Recently, eight species were recognized for the genus Wallemia, among which four are commonly associated with foods: W. sebi, W. mellicola, W. muriae and W. ichthyophaga. To date, only strains of W. sebi, W. mellicola and W. muriae have been reported to be related to human health problems, as either allergological conditions (e.g., farmer’s lung disease) or rare subcutaneous/cutaneous infections. Therefore, this allergological and infective potential, together with the toxins that the majority of Wallemia spp. produce even under saline conditions, defines these fungi as filamentous food-borne pathogenic fungi.
COBISS.SI-ID: 4702287
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 to colonise 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 Aureobasidium melanogenum and Exophiala dermatitidis, and the extremely halotolerant Hortaea werneckii. 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 degrade proteins (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.
COBISS.SI-ID: 4939855