Metabolomic Profile of the Fungus Cryomyces antarcticus Under Simulated Martian and Space Conditions as Support for Life-Detection Missions on Mars

Biomarker Preservation in Antarctic Sandstones after Prolonged Space Exposure Outside the International Space Station During the ESA EXPOSE-E Lichens and Fungi Experiment

A primary aim of current and future space exploration missions is the detection and identification of chemical and biological indicators of life, namely biomarkers, on Mars. The Mars Sample Return NASA-ESA program will bring to Earth samples of martian soil, acquired from up to 7 cm depth. The ESA Rosalind Franklin rover will search for signs of life in the subsurface (down to a depth of 2 meters), given the highly radioactive conditions on Mars' surface, which are not ideal for life as we know it and for the preservation of its traces. In the frame of the Lichens and Fungi Experiment, small fragments of Antarctic sandstones colonized by cryptoendolithic microbial communities were exposed to space and simulated martian conditions in low Earth orbit for 18 months, aboard the EXPOSE-E payload. Through the use of Raman and infrared spectroscopies, as well as a metabolomic approach, we aimed to detect organic compounds in a quartz mineral matrix. The results show that pigments, such as melanin, carotenoids, and chlorophyll, lipids, and amino acids, maintained their stability within minerals under simulated martian conditions in space, which makes them ideal biomarkers for the exploration of putative life on Mars.

Rhinocladiella similis: A Model Eukaryotic Organism for Astrobiological Studies on Microbial Interactions with Martian Soil Analogs

The exploration of our solar system for microbial extraterrestrial life is the primary goal of several space agencies. Mars has attracted substantial attention owing to its Earth-like geological history and potential niches for microbial life. This study evaluated the suitability of the polyextremophilic fungal strain Rhinocladiella similis LaBioMMi 1217 as a model eukaryote for astrobiology. Comprehensive genomic analysis, including taxonomic and functional characterization, revealed several R. similis genes conferring resistance to Martian-like stressors, such as osmotic pressure and ultraviolet radiation. When cultured in a synthetic Martian regolith (MGS-1), R. similis exhibited altered morphology and produced unique metabolites, including oxylipins, indolic acid derivatives, and siderophores, which might be potential biosignatures. Notably, oxylipins were detected using laser desorption ionization mass spectrometry, a technique slated for its use in the upcoming European Space Agency ExoMars mission. Our findings enhance the understanding of extremophilic fungal metabolism under Martian-like conditions, supporting the potential of black yeasts as viable eukaryotic models in astrobiological studies. Further research is necessary to validate these biosignatures and explore the broader applicability of R. similis in other extraterrestrial environments.

Marine Science Can Contribute to the Search for Extra-Terrestrial Life

Life on our planet likely evolved in the ocean, and thus exo-oceans are key habitats to search for extraterrestrial life. We conducted a data-driven bibliographic survey on the astrobiology literature to identify emerging research trends with marine science for future synergies in the exploration for extraterrestrial life in exo-oceans. Based on search queries, we identified 2592 published items since 1963. The current literature falls into three major groups of terms focusing on (1) the search for life on Mars, (2) astrobiology within our Solar System with reference to icy moons and their exo-oceans, and (3) astronomical and biological parameters for planetary habitability. We also identified that the most prominent research keywords form three key-groups focusing on (1) using terrestrial environments as proxies for Martian environments, centred on extremophiles and biosignatures, (2) habitable zones outside of "Goldilocks" orbital ranges, centred on ice planets, and (3) the atmosphere, magnetic field, and geology in relation to planets' habitable conditions, centred on water-based oceans.

Metagenomics untangles potential adaptations of Antarctic endolithic bacteria at the fringe of habitability

Survival and growth strategies of Antarctic endolithic microbes residing in Earth's driest and coldest desert remain virtually unknown. From 109 endolithic microbiomes, 4539 metagenome-assembled genomes were generated, 49.3 % of which were novel candidate bacterial species. We present evidence that trace gas oxidation and atmospheric chemosynthesis may be the prevalent strategies supporting metabolic activity and persistence of these ecosystems at the fringe of life and the limits of habitability.

Shedding light on the composition of extreme microbial dark matter: alternative approaches for culturing extremophiles

More than 20,000 species of prokaryotes (less than 1% of the estimated number of Earth's microbial species) have been described thus far. However, the vast majority of microbes that inhabit extreme environments remain uncultured and this group is termed "microbial dark matter." Little is known regarding the ecological functions and biotechnological potential of these underexplored extremophiles, thus representing a vast untapped and uncharacterized biological resource. Advances in microbial cultivation approaches are key for a detailed and comprehensive characterization of the roles of these microbes in shaping the environment and, ultimately, for their biotechnological exploitation, such as for extremophile-derived bioproducts (extremozymes, secondary metabolites, CRISPR Cas systems, and pigments, among others), astrobiology, and space exploration. Additional efforts to enhance culturable diversity are required due to the challenges imposed by extreme culturing and plating conditions. In this review, we summarize methods and technologies used to recover the microbial diversity of extreme environments, while discussing the advantages and disadvantages associated with each of these approaches. Additionally, this review describes alternative culturing strategies to retrieve novel taxa with their unknown genes, metabolisms, and ecological roles, with the ultimate goal of increasing the yields of more efficient bio-based products. This review thus summarizes the strategies used to unveil the hidden diversity of the microbiome of extreme environments and discusses the directions for future studies of microbial dark matter and its potential applications in biotechnology and astrobiology.

Prominent Roles and Conflicted Attitudes of Eumelanin in the Living World

Eumelanin, a macromolecule widespread in all the living world and long appreciated for its protective action against harmful UV radiation, is considered the beneficial component of the melanin family (ευ means good in ancient Greek). This initially limited picture has been rather recently extended and now includes a variety of key functions performed by eumelanin in order to support life also under extreme conditions. A lot of still unexplained aspects characterize this molecule that, in an evolutionary context, survived natural selection. This paper aims to emphasize the unique characteristics and the consequent unusual behaviors of a molecule that still holds the main chemical/physical features detected in fossils dating to the late Carboniferous. In this context, attention is drawn to the duality of roles played by eumelanin, which occasionally reverses its functional processes, switching from an anti-oxidant to a pro-oxidant behavior and implementing therefore harmful effects.

Survival, metabolic activity, and ultrastructural damages of Antarctic black fungus in perchlorates media

Evidence from recent Mars landers identified the presence of perchlorates salts at 1 wt % in regolith and their widespread distribution on the Martian surface that has been hypothesized as a critical chemical hazard for putative life forms. However, the hypersaline environment may also potentially preserve life and its biomolecules over geological timescales. The high concentration of natural perchlorates is scarcely reported on Earth. The presence of perchlorates in soil and ice has been recorded in some extreme environments including the McMurdo Dry Valleys in Antarctica, one of the best terrestrial analogues for Mars. In the frame of "Life in space" Italian astrobiology project, the polyextremophilic black fungus Cryomyces antarcticus, a eukaryotic test organism isolated from the Antarctic cryptoendolithic communities, has been tested for its resistance, when grown on different hypersaline substrata. In addition, C. antarcticus was grown on Martian relevant perchlorate medium (0.4 wt% of Mg(ClO4)2 and 0.6 wt% of Ca(ClO4)2) to investigate the possibility for the fungus to survive in Martian environment. Here, the results indicate a good survivability and metabolic activity recovery of the black fungus when grown on four Martian relevant perchlorates. A low percentage of damaged cellular membranes have been found, confirming the ultrastructural investigation.