First Insights into the Bacterial Diversity of Mount Etna Volcanic Caves

Abstract

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.

Microbiological exploration of the Cueva del Viento lava tube system in Tenerife, Canary Islands

“…The second most abundant class was Gammaproteobacteria; in this case, the 11K-white biofilm attained the lower relative abundance (10.47%), and the 3C-yellow and 7G-yellow biofilms reached a relative abundance of 12.24% and 22.63%, respectively, while the 5E-red biofilm attained 19.35%. The high abundances of Actinobacteria and Gammaproteobacteria in lava tubes were already reported by other authors (Gonzalez-Pimentel et al, 2021;Nicolosi et al, 2023;Riquelme, Marshall Hathaway, et al, 2015).…”

Crossiella, a Rare Actinomycetota Genus, Abundant in the Environment

“…Apart from the high abundance in Spanish caves, the high relative abundance of Crossiella in Italian caves is also remarkable. In this regard, Nicolosi et al [55] recorded high relative abundances in four Etna volcano caves. One of them ranged from 62.5 to 77.6%.…”

A New Species of Bryaxis (Coleoptera: Staphylinidae: Pselaphinae) from Mount Etna (Sicily, Italy) and Notes on Its Ecology and Distribution

“…nov. (Figure 1A) zoobank.org:act:7FDBBD26-7549-4E56-9EC5-FE3CD1D053C8 Type material: Holotype: SICILY-Etna Mount: Catania province: Linguaglossa Municipality: Grotta dei Rotoli [SICT1239], 1.488 m, trap 2, 06.I.2022, G. Nicolosi leg., 1 3 of 14 ks, the slopes of Mount Etna have underthe summit areas [15]. These distinctive fostered rich biological diversity (e.g., Sci- [18], Nicolosi et al [19,20]), leading to its e vegetation is frequently affected by volstructure, density, cover, floristic compoa tubes [22]. While the prevailing notion pahoehoe lavas (smooth glassy basalt lava), occurs in aa lava (rough brecciated basalt sidered to have formed on pahoehoe lavas flows (e.g., Calvari [23]).…”

“…All collected sorted in the laboratory, and subsequently d in the section of Animal Biology of the nmental Sciences of University of Catania asurements were taken using iButton datobtained from Etna Volcano's Geological and the opening of eruptive fissures on its flanks, the slopes of Mount Etna have undergone continuous modifications, particularly in the summit areas [15]. These distinctive environmental conditions on Mount Etna have fostered rich biological diversity (e.g., Sciandrello et al [16]; Caruso [17]; Magrini et al [18], Nicolosi et al [19,20]), leading to its recognition as a habitat of great significance. The vegetation is frequently affected by volcanic activities, causing dramatic changes in the structure, density, cover, floristic composition, species richness, and diversity [21].…”

“…ks, the slopes of Mount Etna have underthe summit areas [15]. These distinctive fostered rich biological diversity (e.g., Sci- [18], Nicolosi et al [19,20]), leading to its e vegetation is frequently affected by volstructure, density, cover, floristic compoa tubes [22]. While the prevailing notion pahoehoe lavas (smooth glassy basalt lava), occurs in aa lava (rough brecciated basalt sidered to have formed on pahoehoe lavas flows (e.g., Calvari [23]).…”