This study focuses on the microbial characterization of sedimentary cores extracted from the Selvagens Islands (Madeira, Portugal). Located in the North Atlantic, these volcanic islands form an archipelago consisting of two main islands that emerged during the Oligocene period (25-29 Ma). Renowned for their extraordinary marine and terrestrial biodiversity, these islands harbor many endemic species. Remarkably untouched by human activities, this isolated and undisturbed ecosystem offers an exciting opportunity to investigate preserved biosignatures within rock formations and sedimentary deposits. By analyzing the microbial communities in terrestrial sedimentary cores, we aim to gain insights into the microbial diversity, ecological roles, and survival strategies of these pristine ecosystems. Sediment samples were collected along a gradient on a small slope from Baía das Galinhas, Selvagem Grande Island. Each sedimentary core was sliced into 2 cm wide sections. The most superficial and deepest layers of each core were subjected to a combination of microbiological techniques, including 16S rRNA gene sequencing, metagenomics, and culturing methods, to identify and understand the role of microbial populations present in each sediment core. The DNA-based sequencing analysis revealed a clear predominance of microorganisms belonging to the domain Archaea in all sediment samples, with the phylum Euryarchaeota being the most abundant in all samples. The bacterial phyla Actinomycetota, Pseudomonadota, and Bacillota were also found to a lesser extent. Archaea can thrive in extreme environments such as hot springs, terrestrial and marine sediments, hydrothermal vents, saline lakes, permafrost soils, and siliceous speleothems, where they play essential ecological roles. In this study, we also examined the metabolic pathways and functional capabilities of the microbial communities. First, we observed that the most abundant pathways present in the majority of sediment samples are related to aromatic degradation compounds and chemoheterotrophy. These pathways indicate the capability of microbial metabolism to decompose complex compounds and utilize organic compounds as a source of energy and carbon. On the other hand, we found metabolic pathways related to photosynthetic organisms, as phototrophy is one of the most abundant pathways in the most superficial core layers. This research provides valuable insights into the diversity and functionality of microorganisms in volcanic sediments, emphasizing their adaptability and ecological importance. The identification of novel microorganisms and their unique metabolic traits underscores the significance of studying extreme environments to uncover new biological resources and advance our knowledge of microbial ecology.

This study has been funded by the Portuguese Foundation for Science and Technology (FCTPortugal) through the MICROCENO project (10.54499/PTDC/CTA-AMB/0608/2020). The Spanish National Research Council (CSIC) is acknowledged for the intramural project PIE_20214AT021. N.T.J-M. thanks the Ramón y Cajal research contract (RyC2021-031253-I). Grant TED2021-130683B-C22 funded by MICIU/AEI/ 10.13039/501100011033 and the European Union NextGenerationEU/PRTR is also acknowledged.

Comunicación oral online en Frontiers unbound: exploring extreme environments 12-14 sept 2024 Cluj-Napoca (Romania)