Abstract EANA2025-55

Impact craters and associated impact-generated hydrothermal systems may be favourable for microbial colonization, both on Earth and potentially on other planets. The late Devonian Siljan impact crater in Sweden serves as a key example of how impact craters can sustain deep microbial life hundreds of millions of years after the impact-induced hydrothermal event ceases, and is notably known for significant microbial methane seepage. These crater-related microbial consortia rely on heterotrophy and could obtain the necessary carbon and energy from the hydrocarbons migrating through the impact-induced fracture system. To test this novel idea in a modern environment, bioprospecting for hydrocarbon-degrading microorganisms, particularly fungi, was carried out at the Siljan impact crater. Using the redox indicator 2,6-Dichlorophenol-Indophenol (DCPIP) and Gas Chromatography and Mass Spectrometry (GC-MS) techniques, the potential of the cultured microorganisms to activate the hydrocarbons in the medium was assessed. Eight pure fungal isolates were obtained and confirmed through microscopic and molecular identification, which include: Ascochyta phacae, Penicillium pancosmium, Rhodotorula mucilaginosa, Penicillium citreosulfuratum, Absidia glauca, Fusarium salinense, and Mucor hiemalis. Among these, Penicillium citreosulfuratum emerged as the top performer in the DCPIP assays. GC-MS analysis confirmed hydrocarbon degradation within the samples, even though there were limitations in resolving the peaks. These results demonstrate the potential of Siljan-associated fungi to degrade hydrocarbons and contribute to subsurface carbon cycling, where the substrates produced by these fungi could be used by methanogens within the crater for methane production. This supports the idea that impact craters can serve as long-lived biological systems. The detection of seasonal variations of methane on Mars may indicate that this hydrocarbon cycling could be an interplanetary phenomenon and highlights the need to explore the contributions of heterotrophic life to subsurface carbon cycling beyond purely abiotic factors.