Caves, Craters, Mountains & Lava Tubes

First Insights Into The Bacterial Diversity of Mount Etna Volcanic Caves

By Keith Cowing
Status Report
Microbial Ecology via PubMed
June 13, 2024
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First Insights Into The Bacterial Diversity of Mount Etna Volcanic Caves
Field emission scanning electron microscopy images of “Grotta Catanese I” (GC) samples. Representative FESEM images of the studied samples, depicting A Actinobacteria-like coccoid (with 1-μm diameter) and rod-shaped cells with spiny ornamentation (GC1_1A); B filaments with hairy ornamentation, intermingled with coccoid cells (GC1_1A); and C, D clusters of the diatom Orthoseira roeseana and Humidophila (GC1_2) — Microbial Ecology via PubMed

While microbial communities in limestone caves across the world are relatively understood, knowledge of the microbial composition in lava tubes is lagging behind. These caves are found in volcanic regions worldwide and are typically lined with multicolored microbial mats on their walls and ceilings.

The Mount Etna (Sicily, S-Italy) represents one of the most active volcanos in the world. Due to its outstanding biodiversity and geological features, it was declared Natural Heritage of Humanity by the UNESCO in 2013. Despite the presence of more than 200 basaltic lava tubes, the microbial diversity of these hypogean systems has never been investigated so far. Here, we investigated bacterial communities in four lava tubes of Mount Etna volcano.

Map of Mount Etna (Sicily, Italy) with the location of the sampled lava tubes (A). Source: Google Maps [33]. B Entrance of “Grotta del Santo.” C Entrance of “Grotta Catanese I.” D General view of “Grotta Lunga.” E General view of “Grotta di Monte Corruccio” — Microbial Ecology via PubMed

Field emission scanning electron microscopy (FESEM) was carried out for the morphological characterization and detection of microbial features. We documented an abundant presence of microbial cells with different morphotypes including rod-shaped, filamentous, and coccoidal cells with surface appendages, resembling actinobacteria reported in other lava tubes across the world. Based on 16S rRNA gene analysis, the colored microbial mats collected were mostly composed of bacteria belonging to the phyla Actinomycetota, Pseudomonadota, Acidobacteriota, Chloroflexota, and Cyanobacteria.

Taxonomic compositions of the 12 samples based on the 16S rRNA gene markers (99% ASV cutoff). Identifications reached the genus level with the exception of ASVs identified as uncultured and candidatus bacteria. In brackets (), the affiliation to phylum was included. — Microbial Ecology via PubMed

At the genus level, the analysis revealed a dominance of the genus Crossiella, which is actively involved in biomineralization processes, followed by Pseudomonas, Bacillus, Chujaibacter, and Sphingomonas. The presence of these taxa is associated with the carbon, nitrogen, and ammonia cycles, and some are possibly related to the anthropic disturbance of these caves.

This study provides the first insight into the microbial diversity of the Etna volcano lava tubes, and expands on previous research on microbiology of volcanic caves across the world.

First Insights into the Bacterial Diversity of Mount Etna Volcanic Caves Microb Ecol. 2023; 86(3): 1632–1645. Published online 2023 Feb 8. doi: 10.1007/s00248-023-02181-2 (open access via PubMed)


Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻