Infrared spectra of cyanobacteria and brine mixtures: a planetary analogue for life on Europa

Introduction. Europa, i.e., one of Jupiter's Icy Moons is a fundamental target of interest in the search for life in the solar system. The presence of a tidally heated liquid ocean beneath the moon’s icy shell is the main characteristic that makes it a strong candidate for hosting life [1-2]. In addition to this, the presence of a liquid water ocean in contact with a geothermally active subsurface, e.g., hydrothermal vents, which allows for chemical reactions and thermodynamic disequilibria, is what makes this body of exobiological interest [3]. Other icy moons, such as Ganymede for the Jovian system and Saturn’s moon Enceladus have shown to harbour liquid oceans which could be of exobiological interest [4]. Europa is the primary target of the Europa Clipper mission (NASA – 5- 6) and will also be observed via the JUICE probe (ESA – 7), with the possibility of joint observations from the two spacecraft. Before arriving at the Jovian system, it is of paramount importance to investigate which forms of life could be expected to survive and thrive under Europa’s pressure and temperature conditions, both at the bottom of the ocean and on the moon’s surface, as well as to identify possible biosignatures and assess their detectability by remote-sensing instruments onboard the two probes. Previous studies have already worked on spectral characterisation of isolated bacterial strains such as sulphur-metabolising bacteria, radiation-resistant Deinococcus spp. and Echerichia coli exposed to Europa-like temperature and pressure[8]. Recent works have focused on investigating the adaptability and survivability of microbial communities at pressures compatible with Europa’s depth, below the icy shell [9]. In particular, this work will use desert cyanobacteria [10 and references within] focusing on extremotolerant strains capable of using infra-red light to drive oxygenic photosynthesis. Thanks to the specific characteristics of those microbes they can be exposed to extreme conditions similar to the ones of Europa’s surface in terms of cryogenic temperature, pressure, and mineralogical composition to investigate their possible survivability and adaptability.These studies cope with the end goal to produce biomolecule’s spectroscopic data to compare with remote observations.

Materials and Methods. Different desert cyanobacteria strains from the genus Chroococcidiopsis spp. will be used for this experiment. These photosynthetic bacteria are able to establish both hypolithic (under the rocks) and endolithic (within the rocks) communities, which can survive extreme conditions such as water scarcity and temperature fluctuations, making them prime candidates for exobiological investigations. Their resistance has already been tested under simulated Mars conditions in low Earth orbit [11-12] and in several ground-based laboratory experiments testing their different properties (e.g.: radioresistance, limits of photosynthetic behaviour - [13-14]). In the present study, the biological material, e.g.dried-up/isolated bacteria and rehydrated/mixed bacteria within icy brines, will be exposed to cryogenic temperatures and low pressure in order to assess their metabolic activity upon exposure to Europa-like conditions. The biological material and brine’s evolution will be then followed in-situ via infrared spectroscopy using a Bruker Hyperion FTIR microscope coupled to a cryo-cell (Figure 1).

Figure 1. Cryo-cell coupled to the FTIR microscope.

Perspective. This project is currently a work-in-progress. The in-situ spectroscopic monitoring of the system is expected to produce data on the metabolic activities of the microorganisms and identify possible indicators of their vitality. Such data shall be then compared with currently available remote sensed data of Europa’s surface and future data from the MAJIS instrument [15-16] onboard JUICE. A more general comparison with spectral data from other icy moons of exobiological interest would be considered. One of the last goals of the experiment is to evaluate which biomolecules, e.g., carotenoids-like molecules, and microbes are able to survive in Europa-like conditions to create a potential model able to explain the presence and the composition of the famous “Red Stripes” on Europa’s surface. Understanding the resistance of photosynthetic cyanobacteria on icy moons can also be fundamental for the identification of potential biosignature in extremely cold environments and more in general in ice covered celestial bodies of astrobiological interest.

Acknowledgement. This work is supported by the EU and Regione Campania with FESR 2007/2013 O.O.2.1. SR is supported by the ASI-INAF agreement n.2023-6-HH.0 (Resp.: G. Piccioni).

References. [1] Belton, M. J. S. et al. Science 274, 377–385 (1996). [2] Smith, B. A. et al. Science 206, 927–950 (1979). [3] Pappalardo, R. T. et al. J. Geophys. Res. 104, 24015–24055 (1999). [4] Sagan, C. Space Sci Rev 11, 827–866 (1971). [5] Pappalardo, R. T. et al. Space Sci. Rev. 220, (2024). [6] Phillips, C. B. & Pappalardo, R. T. Eos (Washington DC) 95, 165–167 (2014). [7] Grasset, O. et al. Planet. Space Sci. 78, 1–21 (2013). [8] Dalton, J. B. (2001). [9] del Moral Jiménez, 2023. [10] Billi, D., Baqué, M., Verseux, C., Rothschild, L. & de Vera, J.-P. Desert Cyanobacteria: Potential for space and earth applications. in Adaption of Microbial Life to Environmental Extremes 133–146 (Springer International Publishing, Cham, 2017). [11] de Vera, J.-P. et al. Planet. Space Sci. 74, 103–110 (2012). [12] Baqué, M. et al. Orig. Life Evol. Biosph. 43, 377–389 (2013). [13] Di Stefano, G. et al. Life (Basel) 15, 622 (2025). [14] Billi, D. et al. Applied and Environmental Microbiology 66, 1489–1492 (2000). [15] Poulet F. et al. 2024. Space Sci Rev 220. [16] Piccioni G. et al. 2019. IEEE. pp. 318–323.