Taxonomia, diversidade e estudo da virulência de fungos provenientes do permafrost da Antártica

Abstract

Antarctica differs from the rest of the continents for its uniqueness of habitats, characterized mainly by extreme environmental conditions such as low temperature and availability of water and nutrients, strong winds, dynamic freezing and thawing cycles and a high incidence of ultraviolet radiation. Such habitats are colonized predominantly by microorganisms, which include cold-tolerant cosmopolitan taxa or even those considered endemic. Fungi are among the components of the Antarctic microbiome, and due to their differentiated metabolism, are able to survive and / or colonize different substrates. In Antarctica, permanently frozen soils, called permafrost, harbor rare microbial communities, which can remain preserved for thousands of years. With the intensification of global climate changes, especially with regard to the increase in the temperature of the planet, one of the serious consequences may be the thawing in large portions of permafrost and, consequently, the release of organisms trapped in this ecosystem. For this reason, this thesis aimed to characterize communities of fungi residing in permafrost and its active layer in different islands of the South Shetland archipelago, in the Antarctic Peninsula, by dependent and independent methods of cultivation, as well as to evaluate the potential of in vitro virulence of some of the recovered fungi. In the samples obtained in the Robert, Deception and Livingston islands, in temperatures of 10 and 25 ºC, 213 isolates of cultivable permafrost fungi and 351 of active layer were obtained, classified in 58 taxa, being 27 of permafrost and 31 of active layer. The taxa Bionectriaceae spp., Helotiales spp., Mortierellaceae spp. and Pseudeurotium sp. were dominant in the active layer, while the genera Oidiodendron, Penicillium and Pseudogymnoascus were more abundant in permafrost samples. This was the first report of Pseudogymnoascus in Antarctic permafrost, and of great importance due to its relationship with species of P. destructans, which causes high mortality in bats in North America. In addition, there was a small difference in the rates of diversity between the permafrost and active layer communities, although with great dissimilarity. Analyzing only the permafrost samples from the Robert, Livingston, King George and Deception islands, using cultivation-independent methods (new generation sequencing-NGS), the most abundant phyla detected were Ascomycota, Basidiomycota, Chytridiomycota, Rozellomycota, Mucoromycota, Calcarisporiellomycota and Zoopagomycota, respectively. Altogether, 142 families and 201 genera of fungi were detected in the Antarctic permafrost and 99 taxa belonged to high taxonomic levels, which may represent new species, not yet included in the databases used. The community of non-cultivable fungi identified in permafrost showed high levels of diversity, richness and dominance; however, the rates varied between the islands and samples analyzed, with King George (Thomas Point) being the island with the greatest diversity found. Saprophytes were the most common group detected, while plant and animal pathogens represented the second largest proportion of the diversity of detected fungal sequences, emphasizing the risk of their "release" into the environment as permafrost melts with climate warming. In order to determine whether fungi recovered in the permafrost and active layer represent viable cells or propagules with pathogenic potential, the samples from Robert, Livingston, King George and Deception were processed and subjected to a growth temperature of 37 ° C. After processing, 88 fungal isolates were obtained, classified into 18 taxa, belonging to the genera Alternaria, Aspergillus, Curvularia, Penicillium, Rhodotorula and Talaromyces. All of these isolates were evaluated for their ability to produce extracellular enzymes (phospholipase and proteinase) that assist processes of pathogenicity, as well as resistance to a wide range of pH's and hemolytic activity. The fungi previously reported as human opportunists Aspergillus hiratsukae, Aspergillus thermomutatus and Rhodotorula cf. mucilaginosa were recovered in the Antarctic permafrost and capable of growing at 45 and / or 50 ºC, having positive activity for the production of phospholipase, esterase, proteinase, hemolytic activity and resistance to antifungals. Our results demonstrate that permafrost can harbor viable fungi and that these contrast with the overlapping active layer. The Antarctic Peninsula is the main region on the planet under high impact from global climate change, therefore, its permafrost may be under threat of melting. In this sense, our results warn about the influence of global climate changes and the probable release of microorganisms, with pathogenic potential for humans and other animals, from cold ecosystems to other parts of the world.