The Naked Mole-Rat: An Unusual Organism with an Unexpected Latent Potential for Increased Intelligence?

Naked mole-rats are eusocial, hairless mammals that are uniquely adapted to their harsh, low-oxygen subsurface habitat. Although their encephalization quotient, a controversial marker of intelligence, is low, they exhibit many features considered tell-tale signs of highly intelligent species on our planet including longevity, plasticity, social cohesion and interaction, rudimentary language, sustainable farming abilities, and maintaining sanitary conditions in their self-built complex housing structures. It is difficult to envision how naked mole-rats would reach even higher levels of intelligence in their natural sensory-challenged habitat, but such an evolutionary path cannot be excluded if they would expand their range onto the earth’s surface.EC/FP7/339231/EU/Habitability of Martian Environments: Exploring the Physiological and Environmental Limits of Life/HOM

Evolution of default genetic control mechanisms

We present a model of the evolution of control systems in a genome under environmental constraints. The model conceptually follows the Jacob and Monod model of gene control. Genes contain control elements which respond to the internal state of the cell as well as the environment to control expression of a coding region. Control and coding regions evolve to maximize a fitness function between expressed coding sequences and the environment. 118 runs of the model run to an average of 1.4 x 10^6 `generations' each with a range of starting parameters probed the conditions under which genomes evolved a `default style' of control. Unexpectedly, the control logic that evolved was not significantly correlated to the complexity of the environment. Genetic logic was strongly correlated with genome complexity and with the fraction of genes active in the cell at any one time. More complex genomes correlated with the evolution of genetic controls in which genes were active (`default on'), and a low fraction of genes being expressed correlated with a genetic logic in which genes were biased to being inactive unless positively activated (`default off' logic). We discuss how this might relate to the evolution of the complex eukaryotic genome, which operates in a `default off' mode.Comment: 25 pages, 8 figures, 1 tabl

Variations in climate habitability parameters and their effect on Earth's biosphere during the Phanerozoic Eon

Essential insights on the characterization and quality of a detectable biosphere are gained by analyzing the effects of its environmental parameters. We compiled environmental and biological properties of the Phanerozoic Eon from various published data sets and conducted a correlation analysis to assess variations in parameters relevant to the habitability of Earth's biosphere. We showed that environmental parameters such as oxygen, global average surface temperatures, runoff rates and carbon dioxide are interrelated and play a key role in the changes of biomass and biodiversity. We showed that there were several periods with a highly thriving biosphere, with one even surpassing present day biodiversity and biomass. Those periods were characterized by increased oxygen levels and global runoff rates, as well as moderate global average surface temperatures, as long as no large or rapid positive and/or negative temperature excursions occurred. High oxygen contents are diagnostic of biomass production by continental plant life. We find that exceptionally high oxygen levels can at least in one instance compensate for decreased relative humidities, providing an even more habitable environment compared to today. Beyond Earth, these results will help us to understand how environmental parameters affect biospheres on extrasolar planets and guide us in our search for extraterrestrial life

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

The habitability of Mars is strongly dependent on the availability of liquid water, which is essential for life as we know it. One of the few places where liquid water might be found on Mars is in liquid perchlorate brines that could form via deliquescence. As these concentrated perchlorate salt solutions do not occur on Earth as natural environments, it is necessary to investigate in lab experiments the potential of these brines to serve as a microbial habitat. Here, we report on the sodium perchlorate (NaClO4) tolerances for the halotolerant yeast Debaryomyces hansenii and the filamentous fungus Purpureocillium lilacinum. Microbial growth was determined visually, microscopically and via counting colony forming units (CFU). With the observed growth of D. hansenii in liquid growth medium containing 2.4 M NaClO4, we found by far the highest microbial perchlorate tolerance reported to date, more than twice as high as the record reported prior (for the bacterium Planococcus halocryophilus). It is plausible to assume that putative Martian microbes could adapt to even higher perchlorate concentrations due to their long exposure to these environments occurring naturally on Mars, which also increases the likelihood of microbial life thriving in the Martian brines.EC/H2020/339231/EU/Habitability of Martian Environments: Exploring the Physiological and Environmental Limits of Life/HOM

Functional Traits Co-Occurring with Mobile Genetic Elements in the Microbiome of the Atacama Desert

Mobile genetic elements (MGEs) play an essential role in bacterial adaptation and evolution. These elements are enriched within bacterial communities from extreme environments. However, very little is known if specific genes co-occur with MGEs in extreme environments and, if so, what their function is. We used shotgun-sequencing to analyse the metagenomes of 12 soil samples and characterized the composition of MGEs and the genes co-occurring with them. The samples ranged from less arid coastal sites to the inland hyperarid core of the Atacama Desert, as well as from sediments below boulders, protected from UV-irradiation. MGEs were enriched at the hyperarid sites compared with sediments from below boulders and less arid sites. MGEs were mostly co-occurring with genes belonging to the Cluster Orthologous Group (COG) categories “replication, recombination and repair,” “transcription” and “signal transduction mechanisms.” In general, genes coding for transcriptional regulators and histidine kinases were the most abundant genes proximal to MGEs. Genes involved in energy production were significantly enriched close to MGEs at the hyperarid sites. For example, dehydrogenases, reductases, hydrolases and chlorite dismutase and other enzymes linked to nitrogen metabolism such as nitrite- and nitro-reductase. Stress response genes, including genes involved in antimicrobial and heavy metal resistance genes, were rarely found near MGEs. The present study suggests that MGEs could play an essential role in the adaptation of the soil microbiome in hyperarid desert soils by the modulation of housekeeping genes such as those involved in energy production.EC/FP7/339231/EU/Habitability of Martian Environments: Exploring the Physiological and Environmental Limits of Life/HOM

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

Most definitions of life assume that, at a minimum, life is a physical form of matter distinct from its environment at a lower state of entropy than its surroundings, using energy from the environment for internal maintenance and activity, and capable of autonomous reproduction. These assumptions cover all of life as we know it, though more exotic entities can be envisioned, including organic forms with novel biochemistries, dynamic inorganic matter, and self-replicating machines. The probability that any particular form of life will be found on another planetary body depends on the nature and history of that alien world. So the biospheres would likely be very different on a rocky planet with an ice-covered global ocean, a barren planet devoid of surface liquid, a frigid world with abundant liquid hydrocarbons, on a rogue planet independent of a host star, on a tidally locked planet, on super-Earths, or in long-lived clouds in dense atmospheres. While life at least in microbial form is probably pervasive if rare throughout the Universe, and technologically advanced life is likely much rarer, the chance that an alternative form of life, though not intelligent life, could exist and be detected within our Solar System is a distinct possibility.EC/FP7/339231/EU/Habitability of Martian Environments: Exploring the Physiological and Environmental Limits of Life/HOM

Physicochemical Salt Solution Parameters Limit the Survival of Planococcus halocryophilus in Martian Cryobrines

Microorganisms living in sub-zero environments can benefit from the presence of dissolved salts, as they significantly increase the temperature range of liquid water by lowering the freezing point. However, high concentrations of salts can reduce microbial growth and survival, and can evoke a physiological stress response. It remains poorly understood how the physicochemical parameters of brines (e.g. water activity, ionic strength, solubility and hydration shell strength between the ions and the surrounding water molecules) influence the survival of microorganisms. We used the cryo− and halotolerant bacterial strain Planococcus halocryophilus as a model organism to evaluate the degree of stress different salts assert. Cells were incubated in liquid media at −15°C containing single salts at eutectic concentrations (CaCl2, LiCl, LiI, MgBr2, MgCl2, NaBr, NaCl, NaClO4 and NaI). Four of these salts (LiCl, LiI, MgBr2 and NaClO4) were also investigated at concentrations with a low water activity (0.635) and, separately, with a high ionic strength (8 mol/L). Water activity of all solutions was measured at −15°C. This is the first time that water activity has been measured for such a large number of liquid salt solutions at constant sub-zero temperatures (−15°C). Colony-Forming Unit (CFU) counts show that the survival of P. halocryophilus has a negative correlation with the salt concentration, molecular weight of the anion and anion radius; and a positive correlation with the water activity and anions’ hydration shell strength. The survival of P. halocryophilus did not show a significant correlation with the ionic strength, the molecular weight of the cation, the hydrated and unhydrated cation and hydrated anion radius, and the cations’ hydration bond length. Thus, the water activity, salt concentration and anion parameters play the largest role in the survival of P. halocryophilus in concentrated brines. These findings improve our understanding of the limitations of microbial life in saline environments, which provides a basis for better evaluation of the habitability of extraterrestrial environments such as Martian cryobrines.EC/FP7/339231/EU/Habitability of Martian Environments: Exploring the Physiological and Environmental Limits of Life/HOMEDFG, 414044773, Open Access Publizieren 2019 - 2020 / Technische Universität Berli

Physicochemical Parameters Limiting Growth of Debaryomyces hansenii in Solutions of Hygroscopic Compounds and Their Effects on the Habitability of Martian Brines

The availability of liquid water is a prerequisite for all lifeforms on Earth. In hyperarid subzero environments like the Dry Valleys in Antarctica or the near-subsurface of Mars liquid water might be provided temporarily by hygroscopic substances that absorb water from the atmosphere and lower the freezing point of water. To evaluate the potential of hygroscopic compounds to serve as a habitat, it is necessary to explore the microbial tolerances towards these substances and their life-limiting properties. Here we present a study investigating the tolerances of the halotolerant yeast Debaryomyces hansenii to various solutes. Growth experiments were conducted via counting colony forming units (CFUs) after inoculation of a liquid growth medium containing a specific solute concentration. The lowest water activities (aw) enabling growth were determined to be ~0.83 in glycerol and fructose-rich media. For all other solutes the growth-enabling aw was higher, due to additional stress factors such as chaotropicity and ionic strength. Additionally, we found that the solute tolerances of D. hansenii correlate with both the eutectic freezing point depressions and the deliquescence relative humidities of the respective solutes. Our findings strongly impact our understanding of the habitability of solute-rich low aw environments on Earth and beyond.DFG, 455070607, Salzhaltige Habitate auf dem MarsDFG, 414044773, Open Access Publizieren 2021 - 2022 / Technische Universität Berli

Testing the Hydrogen Peroxide-Water Hypothesis for Life on Mars with the TEGA instrument on the Phoenix Lander

Since Viking has conducted its life detection experiments on Mars, many missions have enhanced our knowledge about the environmental conditions on the Red Planet. However, the Martian surface chemistry and the Viking lander results remain puzzling. Non-biological explanations that favor a strong inorganic oxidant are currently favored (e.g., Mancinelli, 1989; Quinn and Zent, 1999; Klein, 1999, Yen et al., 2000), but problems remain regarding the life time, source, and abundance of that oxidant to account for the Viking observations (Zent and McKay, 1994). Alternatively, a hypothesis favoring the biological origin of a strong oxidizer has recently been advanced (Houtkooper and Schulze-Makuch, 2007). Here, we report about laboratory experiments that simulate the experiments to be conducted by the Thermal and Evolved Gas Analyzer (TEGA) instrument of the Phoenix lander, which is to descend on Mars in May 2008. Our experiments provide a baseline for an unbiased test for chemical versus biological responses, which can be applied at the time the Phoenix Lander transmits its first results from the Martian surface.Comment: 11 pages and 3 figure

Bacterial Growth in Chloride and Perchlorate Brines: Halotolerances and Salt Stress Responses of Planococcus halocryophilus

Extraterrestrial environments encompass physicochemical conditions and habitats that are unknown on Earth, such as perchlorate-rich brines that can be at least temporarily stable on the martian surface. To better understand the potential for life in these cold briny environments, we determined the maximum salt concentrations suitable for growth (MSCg) of six different chloride and perchlorate salts at 25°C and 4°C for the extremotolerant cold- and salt-adapted bacterial strain Planococcus halocryophilus. Growth was measured through colony-forming unit (CFU) counts, while cellular and colonial phenotypic stress responses were observed through visible light, fluorescence, and scanning electron microscopy. Our data show the following: (1) The tolerance to high salt concentrations can be increased through a stepwise inoculation toward higher concentrations. (2) Ion-specific factors are more relevant for the growth limitation of P. halocryophilus in saline solutions than single physicochemical parameters like ionic strength or water activity. (3) P. halocryophilus shows the highest microbial sodium perchlorate tolerance described so far. However, (4) MSCg values are higher for all chlorides compared to perchlorates. (5) The MSCg for calcium chloride was increased by lowering the temperature from 25°C to 4°C, while sodium- and magnesium-containing salts can be tolerated at 25°C to higher concentrations than at 4°C. (6) Depending on salt type and concentration, P. halocryophilus cells show distinct phenotypic stress responses such as novel types of colony morphology on agar plates and biofilm-like cell clustering, encrustation, and development of intercellular nanofilaments. This study, taken in context with previous work on the survival of extremophiles in Mars-like environments, suggests that high-concentrated perchlorate brines on Mars might not be habitable to any present organism on Earth, but extremophilic microorganisms might be able to evolve thriving in such environments.EC/FP7/339231/EU/Habitability of Martian Environments: Exploring the Physiological and Environmental Limits of Life/HOM