Survey and characterization of heat-resistant fungi from cave ecosystems in Puerto Rico

Hot caves represent thermally influenced subterranean habitats where microbial communities may be shaped by elevated temperature and guano-driven nutrient inputs. We surveyed cultivable heat-selected fungi from three Puerto Rico caves (Cueva Culebrones, Cueva Matos, and Cueva Tuna) by incubating soil suspensions at 25 °C (control), 75 °C, or 90 °C for 30 min, followed by cultivation on antibiotic-supplemented media and ITS rDNA sequencing. We recovered 34 thermoresistant isolates, including eight from 75 °C, and 26 from 90 °C treatments, dominated by Eurotialean taxa (e.g., Aspergillus, Penicillium, Talaromyces), along with Cladosporium, Paecilomyces, Trichoderma, Periconia, and one Rhodotorula. Several isolates showed < 95% ITS similarity to described taxa, suggesting potentially undescribed lineages, and some identifications were conservatively retained at the genus level where ITS resolution was limited. This study provides the first targeted inventory of heat-selected fungi from Puerto Rico hot caves and highlights these habitats as reservoirs of unexplored fungal diversity.