# Cold-Adapted Fungi: Goldmine of Biomolecules Applicable in Industry
## 2 Diversity and Ecological Role of Cold-Adapted Fungi  
In 1991, a groundbreaking paper estimated the number of fungi on Earth to be 1.5 million [9]. Advances in molecular methods have considerably enhanced our understanding of this kingdom. Subsequent estimates proposed that there might be as many as 5.1 million fungal species, with only approximately 10% known at the time, indicating that the majority remain undiscovered. Recently, data from culture-dependent and culture-independent surveys have suggested that the number of fungal species on Earth is at least 12 million (ranging from 11.7 to 13.2 million), with the actual diversity likely to be even higher [5]. Research on extremophilic fungi, including psychrophiles, has been relatively under-explored. This oversight primarily stems from the assumption that the complexity of their cellular architecture limits their resilience to extreme environmental conditions. However, it is now established that eukaryotes, particularly fungi, possess the capability to thrive in highly challenging environments. The persistence of fungi in such extreme habitats is attributed to both ecological selection pressures and evolutionary adaptations manifesting at physiological, metabolic, structural, and genetic levels [10; 11]. Psychrophilic yeasts and filamentous fungi are considered the most representative of psychrophilic microorganisms surviving at low temperatures [12]. Due to their extensive adaptations, they can colonize all cold ecological niches on Earth [7]. Depending on the habitat, fungi can comprise 55-89% of the total biomass [10]. Numerous studies have shown that filamentous fungi contribute to primary biomass production [13], play a crucial role in carbon cycling [14], and act as decomposers, simultaneously providing nitrogen and phosphorus in cold ecosystems [7]. These functions are linked to their symbiotic relationships with various plants, lichens, macroalgae, and animals, thereby fulfilling multiple ecological roles (e.g., symbionts, mutualists, saprophytes, and pathogens) [10; 15]. The presence of psychrophilic and psychrotrophic fungi in cold environments, such as permafrost, cold water, glacial ice, offshore polar waters, glaciers, ice sheets, ice shelves, freshwater ice, sea ice, and icebergs, has been confirmed [10; 16; 17]. Apart from alpine, Arctic, Antarctic, and deep-sea environments, cold-adapted fungi are also found in man-made habitats where temperatures are often at or below 0 \({}^{\circ}\)C. [PERSON] et al. stated that cold-adapted fungi could be cosmopolitan, where some propagules could be transported externally but are unable to grow under Antarctic conditions, while other indigenous well-adapted fungi, mainly psychrotolerant, are able to grow and reproduce even at low temperature [11]. Most myological studies are conducted in Antarctica. This unique ecosystem is characterized by a range of challenging environmental conditions, including low temperatures, a scarcity of water due to its arid climate (classified as a cold desert), frequent freeze-thaw cycles, strong winds, and high levels of ultraviolet radiation [11]. Paleobiological and paleoecological research suggests that fungi have inhabited Antarctica since at least the Permian period, functioning as saprophytic decomposers [7; 13]. Numerous soil isolates and those derived from historical artifacts contribute to the decomposition of organic matter through the biosynthesis of various hydrolases, thereby promoting the cycling of carbon and nutrients. Studies confirm the presence of taxa representing the most commonly reported phyla in Antarctica, such as Ascomycota, Basidiomycota, Chytridiomycota, Mortierellomycota, and Mucoromycota. Furthermore, the study identified members of the following fungal phyla that are considered cryptic and poorly known in this region: Blastocladiomycota, Monoblepharomycota, Aphelidiomycota, Basidiobolomycota, and the fungal-likeOomycota [15; 18; 19; 20; 21].