Abstract EANA2025-163

Under its thick ice layer, Europa contains a liquid water ocean where habitable conditions may exist. Chemical disequilibrium may occur due to hydrothermal activity at the ocean floor and a supply of oxidants from the irradiated icy surface. On Earth, chemical disequilibrium drives microbial metabolism, and in subsurface environments, primary production depends on chemolithotrophs, which produce energy from the oxidation of inorganic compounds. To understand the habitability and biosignature formation on Europa it is important to integrate our knowledge of the moon’s conditions with laboratory-based analysis. For this work, we developed a laboratory simulation experiment to study the effects of the physicochemical modelled conditions of Europa’s subsurface ocean on microbial function and physiology.

A high-pressure reactor was used to simulate the pressure (between 0.2 MPa and 30 MPa) associated with the upper region of the ocean[1,2]. Ocean chemistry was simulated based on a metamorphic origin of the ocean[3]. Using this chemical composition, an analogue environment was identified, and the microbial community was used as the inoculum for the biotic experiment. For this, we used a microbial enrichment from Basque Lake, Canada; a magnesium- and sulphate-rich environment characterised by low annual temperatures (-5°C to 8°C, with -45°C peaks)[4]. To condition the microorganisms to the high-pressure conditions, cells were initially grown at ambient pressure, and the pressure was gradually increased every 14 days to a final pressure of 30 MPa.

An increase in pressure did not have a significant impact on the chemical composition of the fluid or the cell abundance. However, diversity indices demonstrated a reduction in microbial diversity with increased pressure, with the genus Pseudodesulfovibrio dominating the microbial community. This organism was later isolated through serial dilutions and sequenced using whole genome sequencing (WGS). Transmission electron microscopy demonstrated that the amount of organic material, potentially extracellular polymeric substances, produced by the cells increased with pressure.

Utilising this approach, we can not only grow microbial communities within a simulated Europa subsurface ocean but also isolate model organisms for future study under the conditions in Europa. This has implications for studying potential habitability and biosignature formation within this putative habitable environment.

 

References: 1) Olsson-Francis et al., (2020) doi.org/10.1016/j.mimet.2020.105883; 2) Marion et al., (2005) doi.org/10.1016/j.gca.2004.06.024; 3) Daswani et al., (2021) doi.org/10.1029/2021GL094143; 4) Buffo et al., (2022) 10.1089/ast.2021.0078