G-Equivalent Acceleration Tolerance in the Eutardigrade Species Hypsibius dujardini

Interstellar space biology via Project Starlight

Our ability to explore the cosmos by direct contact has been limited to a small number of lunar and interplanetary missions. However, the NASA Starlight program points a path forward to send small, relativistic spacecraft far outside our solar system via standoff directed-energy propulsion. These miniaturized spacecraft are capable of robotic exploration but can also transport seeds and organisms, marking a profound change in our ability to both characterize and expand the reach of known life. Here we explore the biological and technological challenges of interstellar space biology, focusing on radiation-tolerant microorganisms capable of cryptobiosis. Additionally, we discuss planetary protection concerns and other ethical considerations of sending life to the stars.

Tardigrade Survival Limits in High-Speed Impacts-Implications for Panspermia and Collection of Samples from Plumes Emitted by Ice Worlds

The ability of tardigrades to survive impact shocks in the kilometer per second and gigapascal range was investigated. When rocks impact planetary surfaces, the impact speeds and shock pressures are in the kilometer per second and gigapascal range. This investigation tested whether tardigrades can survive in impacts typical of those that occur naturally in the Solar System. We found that they can survive impacts up to 0.9 km s^-1, which is equivalent to 1.14 GPa shock pressure, but cannot survive impacts above this. This is significantly less than the static pressure limit and has implications for tardigrade survival in panspermia models. The potential survival of tardigrades in impacts of terrestrial impact ejecta on the Moon is shown to be impossible for the average lunar impact speed of such ejecta. However, a notable fraction (around 40%) of such ejecta impact at vertical speeds low enough to permit survival. Similarly, martian impact ejecta striking Phobos, for example, at a typical impact speed will not permit viable transfer of tardigrade-like organisms, but if a fraction of such material had a lower impact speed, survival may be possible. We also consider the implications of this for the collection of viable samples by spacecraft transiting the plumes of icy water worlds such as Europa and Enceladus. We have found the limit on survival of shocks to be around 1 GPa, which is instrumental in determining appropriate mission scenarios and collection methods for the acquisition of viable materials.

Respiration Measurements of Individual Tardigrades of the Species Richtersius cf coronifer as a Function of Temperature and Salinity and Termination of Anhydrobiosis

Numerous studies have demonstrated that tardigrades in a resting state (tun state) are very resistant to exceptional stress levels in comparison with the resistance observed in multicellular organisms in general. The types of stress include desiccation and radiation, which are also relevant in astrobiological research, and therefore, tardigrades are used as multicellular model organisms. For example, tardigrades have been investigated in the TARSE, TARDIS, RoTaRad, and TARDIKISS projects; their survival has been evaluated according to stressful conditions that prevail in low earth orbit, including the effects of cosmic radiation and microgravity. Despite this interest, the study of tardigrade biology has been severely hampered by the sparsity of appropriate quantitative techniques that inform at the single-organism level. In this study, we present results on mass-specific respiration rates as a function of termination of anhydrobiosis and variations in temperature and salinity, including Mars-analog perchlorate solutions, by using microsensor technology to measure respiration. Based on our results for Richtersius cf coronifer, we estimated the activation energy (50.8 kJ/mole O₂) for its metabolism as well as Q10 for selected temperature intervals. Q10 was constant-∼1.5-between 2°C and 33°C, except for the interval 11-16°C, where Q10 was 5.5. The steady-state mass-specific respiration rate of individuals of Richtersius cf coronifer increased with increasing salinity below the lethal limit, likely representing the energy requirements of its osmoregulatory response. We report the first quantitative data of a tardigrade's metabolic dynamics during the termination of anhydrobiosis, revealing significant variation between individuals. However, we observed a general trend, that is, a high initial metabolic rate after exposure to water. Our approach would allow us to carry out quantitative physiological studies of tardigrades on board of the International Space Station, and thus significantly extend the possibility of studying the response of multicellular organisms in space. Summary statement This article reports on first measurements of mass-specific respiration rates of individual tardigrades of the species Richtersius cf coronifer during termination of anhydrobiosis as well as measurements of the impact of temperature and salinity on oxygen uptake rates.

The Emergence of the Tardigrade Hypsibius exemplaris as a Model System

The success of scientists in revealing biological mechanisms has depended in large part on choosing tractable model systems. In 1997, molecular phylogenetics revealed that two of biology's most tractable models-Caenorhabditis elegans and Drosophila-are much more closely related to each other than had been thought previously. I began to explore whether any of the little-studied members of this branch of the tree of life might serve as a new model for comparative biology that could make use of the rich and ongoing sources of information flowing from C. elegans and Drosophila research. Tardigrades, also known as water bears, make up a phylum of microscopic animals. The tardigrade Hypsibius exemplaris (recently disambiguated from a closely related species, Hypsibius dujardini) can be maintained in laboratories and has a generation time of <2 wk at room temperature. Stocks of animals can be stored frozen and revived. The animals and their embryos are optically clear, and embryos are laid in groups, with each synchronous clutch of embryos laid in a clear molt. We have developed techniques for laboratory study of this system, including methods for microinjection of animals, immunolocalization, in situ hybridization, RNA interference, transcriptomics, and methods for identifying proteins that mediate tolerance to extreme environments. Here, I review the development of this animal as an emerging model system, as well as recent molecular studies aimed at understanding the evolution of developmental mechanisms that underpin the evolution of animal form and at understanding how biological materials can survive extreme environments.

Caenorhabditis elegans Tolerates Hyperaccelerations up to 400,000 x g

One of the most important laboratory animal species is the nematode Caenorhabditis elegans, which has been used in a range of research fields such as neurobiology, body development, and molecular biology. The scientific progress obtained by employing C. elegans as a model in these areas has encouraged its use in new fields. One of the new potential applications concerns the biological responses to hyperacceleration stress (g-force), but only a few studies have evaluated the response of multicellular organisms to extreme hypergravity conditions at the order of magnitude 10⁵ x g, which is the theorized force experienced by rocks ejected from Mars (or similar planets). Therefore, we subjected the nematode C. elegans to 400,000 x g (equivalent to that force) and evaluated viability, general morphology, and behavior of C. elegans after exposure to this stress. The metabolic activity of this nematode in response to the gravitational spectrum of 50-400,000 x g was also evaluated by means of the MTT assay. Surprisingly, we found that this organism showed no decrease in viability, no changes in behavior and development, and no drastic metabolic depression after hyperacceleration. Thus, we demonstrated for the first time that this multicellular research model can withstand extremely high g-forces, which prompts the use of C. elegans as a new model for extreme hypergravity. Key Words: Caenorhabditis elegans-Hypergravity-Ultracentrifugation-Acceleration-Panspermia-Astrobiology. Astrobiology 18, 825-833.