Abstract EANA2025-122

Iron-rich minerals, such as hematite (Fe₂O₃), are key components of the Martian surface and serve as potential indicators of past aqueous activity and habitability. In this study, we investigated the interaction between the extremophilic black yeast Rhinocladiella similis LaBioMMi 1217 and hematite under simulated laboratory conditions, with a focus on redox-mediated dissolution processes, metabolic adaptations, and biosignature formation. Given the abundance of iron oxides in Martian regolith and the growing recognition of fungal roles in iron cycling, this work contributes to a better understanding of microbe–mineral interfaces in astrobiological contexts. The fungus was cultivated in the presence of powdered hematite and polished chips in a culture medium, and its impact on mineral alteration was monitored by tracking physical chemical variation and morphology by scanning electron microscopy. Over a 15 days incubation period, the fungal system exhibited pronounced acidification (pH decreased from 7.0 to 5.7) and a significant increase in dissolved Fe²⁺ concentration (from 26 to 270 mg/L), suggesting metabolically mediated iron reduction. SEM images revealed topographical changes in hematite, such as surface corrosion and localized roughness, absent in abiotic controls. These morphological modifications indicate microbial weathering, likely mediated by secreted metabolites with redox activity at the mineral surface. To investigate the underlying molecular mechanisms, genomic mining of R. similis was performed, revealing genes associated with both siderophore biosynthesis (e.g., SidA, SidF, SidI) and reductive iron assimilation (FET3, FTR1, FRE1). Genomic mapping indicated the presence of functionally coherent gene clusters and potential regulatory organization, including regions with multiple copies of iron-related genes. Untargeted metabolomic analysis via mass spectrometry confirmed the excretion of organic acids, iron-chelating compounds, and redox-active metabolites in the presence of hematite. Metabolites such as ferricrocin, and aromatic compounds were positively regulated, indicating a multifaceted fungal strategy combining acidification, chelation, and redox mediation for iron bioremediation. Collectively, our findings demonstrate that R. similis promotes hematite dissolution via organic molecule-mediated mechanisms. This interaction has significant implications for astrobiology, particularly in the search for biosignatures on Mars, where hematite is abundant and may preserve traces of past microbial activity. The ability of fungi to modify mineral substrates and generate diagnostic metabolic imprints positions them as valuable model organisms for exploring life in extreme and extraterrestrial environments.