121-7 Persistence and recovery of extremophilic microbial communities after a tectonic disturbance to a hot sulfidic cave

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

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Authors:

Abstract:

Grotta Nuova di Rio Garrafo is a thermal sulfuric acid cave near Acquasanta Terme, Italy. Hot, deep-seated groundwaters with high levels of dissolved hydrogen sulfide (H₂S) rise to the water table, where rapid H₂S degassing and thermal air currents drive a high flux of H₂S to the cave atmosphere. Earlier studies showed that white biofilms in sulfidic cave streams were formed by filamentous Epsilonproteobacteria and contained novel microbial populations divergent from those found other sulfidic caves. On cave walls, extremely acidic, pH 0-1 biofilms were formed by dense but low-diversity communities dominated by sulfide-oxidizing Acidithiobacillus spp. and Ferroplasma spp., along with other rare acidophilic bacteria and archaea.

In the late 2010s, Grotta Nuova changed following a tectonic event that, at least locally, lowered the sulfidic water table and directed streamflow away from some cave passages. We took advantage of this opportunity to evaluate how the extremophilic microbial communities responded to the disappearance of H₂S(g) from the cave atmosphere. In 2019, three years after the event, the surfaces of secondary gypsum and elemental sulfur deposits in an abandoned stream passage still had acidophilic populations of archaea and bacteria, although relatively fewer Ferroplasma and overall higher microbial diversity compared to similar wall deposits in passages that were still sulfidic. However, by 2022, sulfidic waters had returned to the abandoned passages, with re-established stream biofilms and acidic wall communities that appeared similar to its pre-disturbance state. We will discuss the ecological and astrobiological implications of short-term overprinting by new microbial taxa when sulfidic streams were redirected, the rapid recovery that occurred once the sulfidic waters returned, and the consequences of seismic events for sulfuric acid speleogenesis and the evolution of subterranean chemosynthetic ecosystems.

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

doi: 10.1130/abs/2025AM-10845

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