121-2 Fungal diversity and dynamics along geochemical gradients in a sulfuric acid cave

Session: Caves and Karst Through Space and Time: Biogeochemistry, Climate, and Astrobiology

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Abstract:

Sulfuric acid caves, such as the Frasassi Cave system, are unique environments where microbial activity plays an important role in speleogenesis and nutrient cycling. Bacterial communities on the cave walls and ceilings oxidize hydrogen sulfide (H₂S), producing sulfuric acid that dissolves limestone and forms gypsum deposits. In addition to these chemolithoautotrophic bacteria and archaea, fungi may contribute to cave biogeochemistry by acting as decomposers of organic matter and could play a role in cave development by bioweathering and biomineralization processes. Fungi are multicellular and unicellular eukaryotic organisms known for their extraordinary nutrient cycling abilities, and occur in most environments on Earth. Yet, comprehensive studies on fungi in caves and other subsurface environments have only recently emerged as a significant research focus, and fungi and their ecological roles in sulfuric acid caves are still largely unknown. Therefore, in this study, we aim to characterize fungal communities on the walls of the Frasassi Caves, a sulfuric acid cave system in central Italy, and investigate their presence and diversity near H₂S emissions from cave streams. To achieve this, we are comparing amplicon libraries generated from three different primer sets targeting the 18S rRNA gene and intergenic transcribed spacer (ITS) regions for their suitability for fungal analysis in sulfidic cave environments. Preliminary results reveal a diverse fungal community, with distinct compositions among different chambers within the cave. Basidiomycota was the most abundant phylum in the 18S rRNA gene libraries, while Ascomycota and Basidiomycota were the most abundant phyla in the ITS1 and ITS2 datasets, respectively. Although additional sampling points are needed to establish a better trend in diversity across the H₂S gradient, results to date indicate consistently high diversity across most samples, although communities near the H₂S-degassing streams are less diverse. Our results also show that unclassified fungi were abundant in the ITS libraries, leaving open questions about potential novel fungi in these caves. This study draws attention to microbial eukaryotic life in extreme environments in the terrestrial subsurface and begins to explore how they contribute to biogeochemical cycling and speleogenesis.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8521

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