Caves and other subterranean ecosystems are characterized by stable, low temperatures, high humidity, and limited nutrient input, creating unique environments for extremophilic microorganisms. Among them, fungi play key roles in organic matter degradation, mineral interactions, and biogeochemical cycling, yet the diversity and adaptations of cold-adapted fungi in cave habitats remain insufficiently explored. This study investigated psychrophilic and psychrotolerant fungi inhabiting the stone surfaces of Ravništarka Cave in Eastern Serbia. Biofilm samples were collected from nine sites and analyzed using culture-based isolation on both nutrient-rich and diluted media, followed by incubation at 10 °C, 25 °C, and 37 °C. Fungal identification combined morphological characteristics with molecular analyses of the ITS region and BenA gene, while ecological roles were assigned using FUNGuild. A total of 41 fungal species were documented, spanning Ascomycota (53.1%), Basidiomycota (43.7%), and Mortierellomycota (3.1%) phyla. The genus Penicillium exhibited the greatest species richness, with 14 taxa documented, including P. chrysogenum, P. glandicola, and P. solitum, all previously associated with cold or oligotrophic environments. The psychrotolerant species Mortierella alpina was the only representative of Mortierellomycota. Ecological guild assignment revealed fungi functioning at different trophic levels, highlighting their multifunctional ecological roles in extreme subterranean habitats.

Lampenflora, a complex phototrophic community that develops near artificial light in show caves, is recognized as a major concern for cave management and its regular monitoring has become necessity. For the purpose of this work, the monitoring was performed in one of the most visited show caves in Serbia—Resavska Cave, directly before and after the main season in 2021 in March and November. Lampenflora was localized and developed mainly near the artificial light, but further parts of the cave were not affected by it. Different sampling sites (twelve in total) regarding the type of artificial light and the type of biofilm were chosen for the lampenflora sampling. Two biofilm types were recognized in situ: the epilithic/endolithic ones which were dominated by algae and/or Cyanobacteria and the moss-dominated biofilms. An analysis of the phototrophic microorganisms revealed the presence of Cyanobacteria, Chlorophyta and Bacillariophyta. The highest diversity was found among the Cyanobacteria where the genera Aphanocapsa, Eucapsis, Gloeocapsa and Leptolyngbya were recorded during both of the samplings, Nostoc and Synechocystis were recorded in March, while Hassalia, Oscillatoria and Pseudocapsa were only recorded in November. Chlorophyta were represented by Chlorella, Desmococcus, Klebsormidium, Mesotaenium and Stichococcus in March, and they were represented by same taxa except for Klebsormidium in November. Humidophila was the most widespread diatom in the fresh biofilm samples. Aside from there being higher a level of diversity of it, Cyanobacteria were sporadically found in the samples except on two sampling sites where Aphanocapsa cf. muscicola and Hassalia sp. were abundant. Chlorophyta dominated the samples, which is in accordance with many other studies. The ecological parameters—temperature, relative air humidity, light intensity, substratum moisture and substratum pH were also determined and related to a degree of colonization and the community composition.

Cave microbiota comprise metabolically diverse organisms, including microalgae, among which Bacillariophyta (diatoms) represent one of the most prominent groups, inhabiting a wide range of substrates within cave ecosystems. In contrast to aerophytic cave habitats, aquatic cave environments remain poorly studied. Therefore, the main aims of this study were to determine the diversity, spatial distribution, and seasonal dynamics of diatom assemblages in the Ponorac Stream flowing through Ravništarka Cave, and to assess the influence of environmental variables on diatom diversity and distribution. Samples were collected from six sites along the Ponorac stream in May and November 2023. Physical and chemical water parameters showed only minor variation among sampling sites. In total, 148 diatom taxa belonging to 54 genera were recorded, including several rare diatom taxa. Diatom assemblages in the Ponorac stream were characterized by high taxonomic richness, high α-diversity, and pronounced community heterogeneity. Many taxa occurred in both seasons and across multiple sites, whereas several were restricted to a single season or exhibited clear site specificity. Most diatom index values indicated generally high ecological status. This study highlights the importance of aquatic cave habitats as reservoirs of diatom diversity and their value in studying temporal and spatial variation of their communities.

Thermomineral springs provide stable thermal and geochemical regimes that promote the development of dense phototrophic biofilms dominated by cyanobacteria. Phototrophic communities were investigated across eight thermomineral springs in Serbia (six in eastern and two in central Serbia) using an integrated morphological, ecological, and molecular approach. Biofilms were sampled in 2024 from contrasting microhabitats (submerged, overflow, and splash/aerosol-exposed zones) and biomass was assessed through chlorophyll a (Chl a) quantification. Cyanobacterial taxa were identified via light microscopy using standard taxonomic keys and simple trichal morphotypes represented the highest diversity; Leptolyngbya showed the broadest distribution, while heterocytous taxa (Calothrix) were rare. A total of 73 cyanobacterial taxa were recorded across the eight investigated springs, with richness ranging from 1 to 33 taxa per locality; the highest richness was observed in Brestovac (33 taxa), followed by Šarbanovac (28) and Nikoličevo (22). Molecular characterization (16S rRNA) of nine cultured isolates revealed multiple filamentous cyanobacterial lineages, including Elainella (Oculatellales) and Wilmottia-related clades, while several isolates showed “Leptolyngbya-like” BLASTn affinities but phylogenetically separated clustering. Overall, the results indicate that Serbian thermomineral springs host diverse cyanobacteria-dominated biofilms shaped by local physical and chemical gradients and microhabitat structure and represent promising reservoirs of thermotolerant strains for further biotechnological use.