Abstract EANA2025-105

Early Mars (up to the Middle Noachian period) is believed to have closely resembled Earth during the Palaeoarchaean Era (approximately 3.5 billion years ago), the time when life is thought to have first emerged (Hickman-Lewis et al., 2019, https://dx.doi.org/10.1016/B978-0-444-63901-1.01001-7; Cavalazzi et al., 2021, https://doi.org/10.1007/978-3-030-81039-9_10). Geological, geomorphological, and mineralogical analyses conducted across various regions of Mars have confirmed the presence of sedimentary deposits—especially fluvio-lacustrine ones— which support the hypothesis that, at that time, liquid water may have been persistent and stable on the Martian surface. Such conditions would have enabled the development of essential bioelements and the formation of ecological niches potentially favourable to life.

This period is also thought to have been characterized by a warmer and wetter climate (Di Achille and Hynek, 2010, https://doi.org/10.1038/ngeo891; Grotzinger et al., 2015, https://doi.org/10.1126/science.aac757; Mc Lennan et al., 2019, https://doi.org/10.1146/annurev-earth-053018-060332). In this light, planetary field analogues that reflect sedimentary environments as well as those associated with the secondary volcanic and hydrothermal activity, represent some of the most promising sites for investigating the origins of life on Earth and assessing the habitability and astrobiological potential of early Mars (e.g. Michalski et al., 2018, https://doi.org/10.1038/s41561-017-0015-2).

Lake Bagno dell’Acqua (also known as Specchio di Venere), located on the Pantelleria island (Sicily, Italy), offers a unique natural setting to study the mechanisms that may have driven the possible emergence of life and its adaptations to conditions analogous to those of early Mars. This endoreic lake—it lacks any natural outflow—undergoes significant seasonal variations. It is mainly fed by meteoric water, with a minor contribution from thermal springs located along its margins. The lake is characterized by polyextreme conditions, including intense seasonal evaporation, high water temperatures (up to 60 °C), pH values ranging from slightly acidic to strongly alkaline, and high, fluctuating salinity levels driven by evaporation. Furthermore, the interaction of lake water with volcanic rocks, gases, and thermal fluids contributes to the presence of metals and other chemical elements. In this context, the HELENA project (Extreme Habitats of Volcanic Lakes for Astrobiological Exploration) aims to characterize the microbial diversity—encompassing both prokaryotic and eukaryotic/fungal communities—within this poorly understood polyextremophilic ecosystem. The project seeks to identify specific geochemical factors that influence microbial diversification and spatial distribution across the lake.

To achieve these objectives, during the summer of 2024, samples were collected from microbial mats forming a ring around the lake, at multiple locations along the shoreline, as well as from two hot springs with elevated temperatures, both covered by microbial mats. The total microbial diversity was assessed using a DNA metabarcoding approach targeting archaeal, bacterial and fungal components. The abundance and composition of microbial taxa accross the different sampling sites were compared and correlated with the chemical and physical parameters measured at each location, in order to identify the environmental factors driving community differentiation and the distribution of specific microbial taxa.

The HELENA project is funded by the Italian Space Agency (contract n. 2023-9-U.0).