## 4 Discussion  
Studies on fungal diversity depend on the correct identification of species. Classical identification relies on direct observation of fungi either in their natural condition or after culturing in different growth media [31]. However, currently, mycotaxonomy combines the use of molecular methods along with conventional ones. Such an approach allows discovering new or reinvestigating already known taxa [16; 59]. For example, dermatophytes used to be classified as genera _Trichophyton_, _Epidermophyton_ and _Microsporum_. However, combinatory molecular analyses (sequencing of ITS rDNA, ribosomal 60S subunit, \(\beta\)-tubulin fragments, and translation elongation factor 3) allowed for the reclassification of dermatophytes into the following genera: _Trichophyton_, _Epidermophyton_, _Nannizia_, _Paraphyton_, _Lophophyton_, _Microsporum_, _Arthroderma_, _Ctenomyces_, and _Guarromyces_[60]. In the present study, we followed this trend by using targeted growth conditions (Vanbreuseghem hair bait) as well as a combination of classical and molecular identification approaches in order to report the occurrence of keratin-dependent fungal species in three studied caves (Brestovska, Demanovska Ladova and Demanovska Slobody) belonging to the Tatras Mountains in north Slovakia. The interest in soil mycobiota capable of keratin degradation originates in two factors: the biochemical resistance of keratin and the pathogenic potential of keratinocyte saprophytic species [61]. In the present paper, we followed the broad definition of keratin-associated fungi, which divides them into keratinocyte and keratinophilic species. Accordingly, keratinocyte fungi are able to utilize keratin, while keratinophilic fungi utilize non-keratinous components of keratinous substrata or by-products of keratin degradation [62]. In natural environments, the presence of keratin-associated fungi depends on the availability of keratinic substrata of animal or human origin [63]. The constant flow of such organic matter has been associated with the distribution of keratinocyte fungi in environments such as arable soils [64; 65; 66; 67], sewage sludge and river bottom sediments [68; 69], compost [70], bird feathers [71], the deposits of free-living rodents [72], the nests of water birds [73], and pellets of birds of prey [74]. Keratinolytic fungi are classified as dermatophytes and _Chrysosporium_, or according to [PERSON] (2009) into two orders: Onygenales and Eurotiales [75]. [PERSON] (2000) emphasized that fungi belonging to Onygenales are highly specialized in keratin degradation and include six genera, namely _Arthroderma_, _Aphanosus_, _Epidermophyton_, _Microsporum_, _Trichophyton_, and _Chrysosporium_[76]. However, the diversity of keratinocyte species is considered to be much broader [67; 77] and includes species from the genera _Trichoderma_, _Fusarium_, _Cludosporium_, _Phyophthora_[78], and _Talamovacs_[79], as well as _Aspergillus niger_ and _Aspergillus fumigatus_[71]. In fact, the definition can be even wider as some species or genera are newly reported to be keratin-dependent, such as _Pseudogymnucas destructants_[80]. It should be emphasized that underground objects display harsh living conditions for microorganisms because they are heterotrophic ecosystems (with few exceptions, e.g., the Movie Cave \"Pestera Movie\" in Romania, a sulfur-based chemolitho-313 autotrophic ecosystem [81]) Despite this fact, in this study we reported the presence of 10 keratin-dependent genera, namely _Aphanoascus_, _Arthroderma_, _Aspergillus_, _Chrysosporium_, _Cordycps_, _Cosmospora_, _Keratinophyton_, _Metapoconia_, _Penicillium_, and _Pseudogymnucascus_ (Table 2). All of these belong to the phylum Ascomycota, which is in agreement with [PERSON] [12]. Out of the 18 different fungal species identified herein, the following were already reported by [PERSON] et al. [12] to colonize underground sites: _A. fumigatus_, _A. quadrifatum_, _A. keratinophilus_ (reported as _Chrysosporium keratinophilium_), _Ch. merdarium_, _C.