Methanogenic Archaea Can Produce Methane in Deliquescence-Driven Mars Analog Environments

Abstract

the current understanding of the Martian surface indicates that briny environments at the near-surface are temporarily possible, e.g. in the case of the presumably deliquescence-driven Recurring Slope Lineae (RSL). However, whether such dynamic environments are habitable for terrestrial organisms remains poorly understood. this hypothesis was tested by developing a closed Deliquescence System (CDS) consisting of a mixture of desiccated Martian Regolith Analog (MRA) substrate, salts, and microbial cells, which over the course of days became wetted through deliquescence. The methane produced via metabolic activity for three methanogenic archaea: Methanosarcina mazei, M. barkeri and M. soligelidi, was measured after exposing them to three different MRA substrates using either NaCl or naclo 4 as a hygroscopic salt. Our experiments showed that (1) M. soligelidi rapidly produced methane at 4 °C, (2) M. barkeri produced methane at 28 °C though not at 4 °C, (3) M. mazei was not metabolically reactivated through deliquescence, (4) none of the species produced methane in the presence of perchlorate, and (5) all species were metabolically most active in the phyllosilicate-containing MRA. These results emphasize the importance of the substrate, microbial species, salt, and temperature used in the experiments. Furthermore, we show here for the first time that water provided by deliquescence alone is sufficient to rehydrate methanogenic archaea and to reactivate their metabolism under conditions roughly analogous to the near-subsurface Martian environment. Methane in the atmosphere of Mars was first detected by Formisano, et al. 1 with the Planetary Fourier Spectrometer onboard the Mars Express orbiter. Recent measurements by the Tunable Laser Spectrometer onboard the Curiosity rover show that methane concentrations are currently in the parts per billion range and fluctuate repeatedly throughout the seasons 2. However, the long-term stability and presence of methane in the Martian atmosphere is considered unlikely over geological time periods due to degradation by UV radiation and/ or oxidizing compounds at the surface 3. Hence, it has been proposed that subsurface reservoirs might sporadically release methane and/or that it is actively produced through abiotic, or potentially, as it is on Earth, from microbial processes 4. On Mars, however, the environmental conditions within the surficial regolith generally do not permit a lasting presence of liquid water necessary for microbial metabolism. Nevertheless, besides surficial monolayers of liquid-like water 5 and morning frost 6 , a possible exception are near-surface environments laden with hygroscopic salts which can undergo deliquescence, a process occurring when the relative humidity (RH) exceeds the deliquescence relative humidity (DRH) of a given salt above its eutectic temperature. Such a mechanism was first hypothesized by McEwen, et al. 7 to play a role in the seasonal surface features on Mars known as Recurring Slope Lineae (RSL), dark streaks that appear on steep crat...

Microbial Hotspots in Lithic Microhabitats Inferred from DNA Fractionation and Metagenomics in the Atacama Desert

“…Both Salinibacter and members of the Halobacteriales have unique molecular adaptations allowing them to overcome the low water activity and the extremely high salt environment [ 104 , 105 , 106 ]. Microbial life may also benefit from the ability of halite nodules to undergo deliquescence by absorbing moisture from their surroundings and providing water to the halite microbial community in the form of concentrated brine [ 33 , 83 , 103 , 107 ]. However, the limited presence of these ASVs in the corresponding eDNA pool is an indicator for slow replication rates, pointing to a unique microbial community which can only be active from time to time, e.g., after a rare rain event or when fog drifts far inland.…”

The Astrobiology of Alien Worlds: Known and Unknown Forms of Life

“…That process is called deliquescence and is used by some microbes, especially cyanobacteria, as a means of survival [109] (Figure 3). In recent lab experiments, archaea survived and metabolized with 100% of water supplied only by deliquescence [110]. Another means of survival is the hypolithic lifestyle.…”

“…In situ evidence for microbial life on Mars remains controversial [7,108], but newer and more capable instruments than the Viking landers, either on their way or in development for delivery to Mars, such as the ExoMars Lander [167], demonstrate the potential for robotic collection of relevant data. Numerous studies of analog environments on Earth likewise should continue to shed light on possible forms of life on a barren planet like Mars [108,110,168,169].…”

A New Record for Microbial Perchlorate Tolerance: Fungal Growth in NaClO4 Brines and its Implications for Putative Life on Mars

“…On Earth, most of the salt-rich habitats are based on sodium chloride (NaCl), e.g., in the Atacama Desert, Chile, where endolithic cyanobacteria thrive in NaCl crusts by gaining water absorbed by the salt [14,15]. Furthermore, it has also been shown very recently that methanogenic archaea can survive saturated NaCl concentrations and use water exclusively provided by the deliquescence of salt [16]. There are several environments on Earth that also provide high concentrations of salts other than NaCl, e.g., the Dead Sea with increased calcium (0.47 M Ca 2+ ) and magnesium (1.98 M Mg 2+ ) chloride concentrations (additional to saturated NaCl conditions) [17], the Spotted Lake (Canada) containing high sulfate concentrations (>3 M) [18], the Don Juan Pond (Antarctica) containing 3.7 M CaCl 2 [19,20], or the Discovery Basin (Mediterranean Sea) containing 5 M MgCl 2 [21].…”