First Insights into the Bacterial Diversity of Mount Etna Volcanic Caves

14 páginas.- 8 figuras.- 1 tabla.- 93 referencias.- Supplementary Information The online version contains supplementary material available at https://doi.org/10.1007/s00248-023-02181-2

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. 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. 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.

Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. This work was supported by the Spanish Ministry of Science and Innovation (MCIN) under the research project TUBOLAN PID2019-108672RJ-I00 funded by MCIN/AEI/ 10.13039/501100011033. In addition, this work received support from the Portuguese Foundation for Science and Technology (FCT) under the MICROCENO project (PTDC/CTA-AMB/0608/2020), and from the Spanish National Research Council (CSIC) through the intramural project PIE_20214AT021. A.Z.M. was supported by the CEECIND/01147/2017 contract from FCT and the Ramón y Cajal contract (RYC2019-026885-I) from the MCIN.

Peer reviewed