Entombment of microbial biomass within rapidly frozen fluid droplets relevant to the plumes of Enceladus

• DOI: 10.5194/epsc2022-1230
• Publication Date: 2022-09-23T13:09:19Z
• Authors: Mark Fox-Powell; Álvaro del Moral; Ben Stephens; Connor Dazley; David Slade; Grace Richards; Claire Cousins; Karen Olsson-Francis
• Keywords: Enceladus; Icy moon

<p><strong>Introduction.</strong> The plumes emanating from the south polar region of Saturn’s moon Enceladus were studied by Cassini mission and have revealed evidence for ongoing hydrothermal activity [1], organic chemistry [2], redox conditions favorable microbial metabolism [3] in ocean below. Salt-rich icy particles encountered interpreted to originate as rapidly frozen droplets spray [4]. If extant communities exist within Enceladus’s ocean, cells may become incorporated into these ejected space where they can be sampled future spacecraft [5]. However, potential fate biomass is not understood. Here, we used cryogenic imaging alongside sublimation-extraction techniques study interaction microorganisms with precipitated inorganic phases during freezing simulated fluids, at contrasting cooling rates. Our findings reveal how expressed plumes, carry implications its detection using current sampling strategies</p> <p><strong>Methods:</strong> Cells taken four phylogenetically morphologically distinct pure cultures, well a mixed community, suspended fluid [6], cooled two rates: quench liquid nitrogen (10<sup>1</sup>-10<sup>2</sup> K s<sup>-1</sup>), gradual (0.01 s<sup>-1</sup>). Partitioning ice non-ice droplet interiors was imaged 120 via cryo-scanning electron microscopy. Specific associations between mineral analyzed cryo-electron microscopy, mineralogy crystalline precipitates determined infrared spectroscopy X-ray diffraction (XRD) following extraction matrix sublimation.</p> <p><strong>Results discussion:</strong> Under both scenarios, crystallisation produces an interconnected network solidified solute-rich brine veins accumulated grain boundaries, which intact entombed (Fig. 1). presence also leads formation small, solitary inclusions fully encased ice, are disconnected main vein network. Microscale crystallization textures, previously identified diagnostic rate disrupted modified biomass, differences arising inclusions. XRD analyses salt shows that influences bulk 2). In absence nahcolite (NaHCO<sub>3</sub>) kinetically inhibited flash freezing. does form freezing, resulting instead resembles gradually control fluids. This indicates favors precipitation nahcolite. Moreover, this finding provides route could influence plumes. Given sensitive pH plume should prioritized observations.</p> <p>Our results demonstrate preserved relevant revealing complex, rate-dependent interactions precipitating phases. association specific has interpreting secondary ion fragments impact-ionization mass spectra [7], planning missions target situ analyses, or more ambitiously, sample return.</p> <p><strong>References:</strong> <strong>[1]</strong> Waite, J. H. et al. Science 356, 155–159 (2017). <strong>[2]</strong> Postberg, F. Nature 558, 564–568 (2018). <strong>[3]</strong> Ray, C. Icarus 364, 114248 (2021). <strong>[4]</strong> Postberg 459, 1098-1101 (2009). <strong>[5]</strong> Porco, C.C., Astrobiology, 17, 876-901 <strong>[6]</strong> Fox-Powell & Cousins, JGR: Planets 126(1), e2020JE006628 <strong>[7]</strong> Klenner Astrobiology 20, 1168-1184 (2020).</p> <p><img src="" alt="" /></p> <p><strong>Figure 1.</strong> (Cryo) micrographs co-partitioned biomass. A, B., Cryo-SEM images E. coli cell. C., Solitary inclusion. D., textures.</p> 2.</strong> patterns assemblages produced community enrichments. ‘Control’ trace represents samples H: halite (NaCl); T: Trona (Na<sub>2</sub>CO<sub>3</sub>•NaHCO<sub>3</sub>•2H<sub>2</sub>O); N: Nahcolite (NaHCO<sub>3</sub>).</p>