Tardigrades in Space

Abstract:-

This article explores the remarkable adaptations of tardigrades, and microscopic water bears, including their ability to undergo cryptobiosis—a reversible state induced by extreme conditions. Tardigrades, thriving in harsh limno-terrestrial habitats, exhibit resilience to desiccation, freezing, and other stressors. The study emphasizes the physiological intricacies of cryptobiosis, protective mechanisms like “tun” formation, and the species Richtersius coronifer's survival in extreme environments. Tardigrades, deemed "superpowered" by entering cryptobiosis, play a crucial role in astrobiology and space research, showcasing their resilience to space vacuum, radiation, and high temperatures. Radiation tolerance studies reveal unexpected efficiency in DNA repair mechanisms, challenging previous assumptions. At the end of this Article ,lists of all Hard words and Scientific terms are given for better understanding.

Introduction:-

Tardigrades are microscopic animals found worldwide in aquatic as well as terrestrial ecosystems. They belong to the invertebrate superclade Ecdysozoa, as do the two major invertebrate model organisms: Caenorhabditis elegans and Drosophila melanogaster. Tardigrades, known as water bears, are microscopic metazoans (approximately 0.1–1.2 mm). They were discovered in the 18th Century.

Tardigrades are uniquely adapted to a range of environmental extremes. Cryptobiosis, currently referred to as a reversible ametabolic state induced by e.g. desiccation, is common, especially among limbo-terrestrial species. It has been shown that the entry and exit of cryptobiosis may involve the synthesis of bioprotectants in the form of selective carbohydrates and proteins as well as high levels of antioxidant enzymes and other free radical scavengers (N. M?bjerg, 2011)

Adaptation to extreme environment:-?

Tardigrades, renowned for their tolerance to extreme conditions, thrive in limo-terrestrial habitats prone to drying out, freezing, and experiencing significant fluctuations in osmotic pressure and oxygen tension. Four traditionally recognized physical extremes inducing cryptobiosis include dehydration (anhydrobiosis), extremely low temperatures (cryobiosis), lack of oxygen (anoxybiosis), and high salt concentration (osmobiosis). Desiccation-induced anhydrobiosis and freezing-induced cryobiosis are the most extensively studied states.

The anhydrobiotic state is characterized by the formation of a protective structure called a "tun," where tardigrades withdraw their legs and contract their bodies actively. Tun formation is an essential adaptation to desiccation, and recent research indicates its activation in response to environmental toxins, termed chemobiosis. Despite their microscopic size, tardigrades in the tun state exhibit remarkable resilience to various stressors, including desiccation, exposure to toxic chemicals, subzero temperatures, vacuum, high pressure, radiation, extreme pH, anoxia, and to some extent, high temperature.Adaptations to these extremes are believed to involve the synthesis of bioprotectants, such as selective carbohydrates and proteins, high levels of antioxidant enzymes, specific phospholipids in biological membranes, and potent DNA repair mechanisms. Some tardigrade species additionally form cysts and enter diapause as alternative strategies for survival. Remarkably, even in their active states, tardigrades display high tolerance to environmental stress. Understanding the normal physiology of tardigrades is essential to unravel the mechanisms behind their exceptional stress tolerance, as exemplified by the littoral eutardigrade Halobiotus crispae, which exhibits seasonal cyclic changes in morphology and physiology, including a freeze-tolerant stage during cyclomorphosis. These findings contribute to elucidating the intricate adaptations of tardigrades to diverse and challenging environmental conditions.

Cryptobiosis: The superpower in tardigrades:-

Cryptobiosis is a biological phenomenon where an organism enters a state of extreme metabolic slowdown in response to adverse environmental conditions. This state allows the organism to endure harsh conditions that would normally be lethal, such as extreme temperatures, desiccation (extreme drying), high levels of radiation, or lack of water. Essentially, the organism can shut down its metabolic processes and become almost completely inactive until more favorable conditions return.

The ability to enter cryptobiosis has implications for various scientific fields, including Astrobiology and Space research, as these microscopic organisms demonstrate remarkable resilience in the face of environmental challenges

Richtersius coronifer, a type of water bear, is known for its exceptional ability to endure extreme conditions, including desiccation and freezing. This tiny creature, up to 1 mm in size, lives in moss in cold environments. In experiments, R. coronifer {species} demonstrated true cryptobiosis, surviving desiccation and exposure to very low temperatures, even as low as -196 °C. Its ability to enter an anhydrobiotic state allows it to endure high temperatures, up to around 70 °C for an hour, though survival decreases beyond this point.

Researchers are exploring the limits of cryptobiotic survival, suggesting potential damage to DNA and other molecules during this state. The longer R. coronifer spends in anhydrobiosis, the more time is needed for recovery after rehydration, indicating significant repair processes. Protective mechanisms during cryptobiosis, such as trehalose accumulation and the expression of heat-shock proteins (HSPs), are under investigation. Trehalose, a sugar, is thought to act as a stabilizer, but its role varies among tardigrades. HSPs, especially Hsp70, are associated with anhydrobiosis, with elevated levels following desiccation, radiation, and heating. However, the role of HSPs differs among tardigrade species.

This complexity underscores the need for more research to understand cryptobiosis fully. Scientists are exploring metabolome profiling and bioprotectants like late-embryogenesis abundant (LEA) proteins for additional insights. Cryptobiosis remains a fascinating and intricate phenomenon that requires further exploration to unveil its underlying mechanisms.

(N. M?bjerg, 2011)

Why are Tardigrades considered Animals ??

Tardigrades commonly known as water bears, a name derived from their resemblance to eight-legged pandas. Tardigrades exhibit a distinctive anatomical structure, comprising five body sections, including a well-defined head and four body segments. Each segment is equipped with a pair of legs that possess claws. The claw appearance varies among species, ranging from a familiar bearlike structure to intriguingly resembling medieval fistfuls of hooked weaponry. Notably, the hindmost legs of tardigrades are uniquely attached backward, an arrangement unparalleled in the animal kingdom. These rear legs serve purposes beyond walking, primarily engaging in grasping and facilitating slow-motion acrobatics. Inside tardigrades, Scientists discovered a setup surprisingly similar to larger animals. They have a complete digestive system, including mouth parts, a sucking pharynx, an esophagus, a stomach, an intestine, and an anus. Despite being small, tardigrades have good muscles, though they only have one reproductive organ.

Tardigrades also have a unique nervous system, with a brain on top and a paired ventral system, which is different from humans with a single dorsal nervous system. Additionally, tardigrades have an open body cavity called hemocoel that reaches every cell. This design helps with effective nutrition and gas exchange without needing circulatory or respiratory systems, showing how adaptable these small creatures are.

Tardigrades in Space Research and Space Missions:-

1. Cell Science-04 Mission:

????The mission involved sending water bears to the ISS aboard the SpaceX Dragon on the CRS-22 mission.

1. Dr. Thomas Boothby was the principal investigator for Cell Science-04.
2. The goal was to understand how tardigrades adapt to space conditions, specifically microgravity.

2. Physical Characteristics of Tardigrades:

1. Tardigrades are microscopic and have a distinctive appearance, resembling chubby, eight-legged gummy bears.
2. They can be transparent or have armored plates on their backs, displaying morphological diversity.

3. Tardigrade Survival Skills:

1. Tardigrades can survive extreme conditions, including desiccation (drying out), freezing, high temperatures, radiation, and the vacuum of outer space.
2. They can enter an ametabolic state, curling up into a ball-like structure called a tun, shutting down life processes, and surviving in harsh environments.
3. Tardigrades can survive for decades or even hundreds of years in this state.

4. Biological Mechanisms for Survival:

1. Tardigrades produce unique proteins when exposed to extreme conditions.
2. These proteins increase the viscosity of their internal environment, slowing down detrimental processes.
3. The increased viscosity forms a glassy material, protecting sensitive molecules inside tardigrade cells.
4. When rehydrated, the glassy material dissolves, releasing the preserved molecules, and allowing normal biological functions to resume.

5. Research Goals and Applications:

1. The Cell Science-04? (NASA Science (.gov), 2021) aims to investigate changes in gene expression in tardigrades exposed to space conditions.
2. Understanding how tardigrades adapt may provide insights into safeguarding astronauts during prolonged space missions.
3. Potential applications include developing therapies or countermeasures for astronauts, such as antioxidants or reactive oxygen species scavengers.

6. Experiment Setup on ISS:

1. Tardigrades will be sent to the ISS in syringes and injected into a bioculture system.
2. Astronauts will need to thaw and inject fresh algae (food source) into the system at two-week intervals.
3. Environmental measurements on the ISS will help replicate experiments on Earth as near-synchronous ground controls.

7. Team Collaboration:

1. The research involves a collaborative effort with a team of researchers, scientists, and support staff from the University of Wyoming, NASA, and KBR.

8. Scalability and Future Research:

1. The research on tardigrades and their adaptations to space conditions is seen as scalable and may continue in future space missions.
2. There is potential for further investigations, especially with upcoming space exploration missions, such as those planned for the Moon.

This information provides a comprehensive overview of tardigrades, their unique survival mechanisms, and the objectives of the Cell Science-04 mission on the ISS. ( NASA Science (.gov), 2021)

Tardigrades have emerged as crucial subjects in space research, stemming from their extraordinary resilience to environmental stressors. Initially proposed as model organisms in 1964 due to their exceptional resistance to radiation, recent studies have increasingly focused on their suitability for astrobiological investigations. J?nsson's 2007 study elucidated the tardigrades' unique ability to endure dehydration, extreme temperatures, and radiation, underscoring their potential as robust model organisms for space exploration.

This remarkable adaptation allows tardigrades to withstand adverse factors encountered in outer space. Their capability to survive in the vacuum of space, coupled with resistance to ionizing radiation and extreme temperatures, positions them as ideal candidates for understanding the limits of life in extraterrestrial environments.

Various space programs have been initiated to explore tardigrades' responses to space conditions. Projects such as TARSE, TARDIS, RoTaRad, and TARDIKISS subjected tardigrades to microgravity, cosmic radiation, and the space vacuum. Findings indicated their resilience, but with nuanced responses to specific stressors. The Phobos Life Project, integrated into the Phobos Ground Mission, aimed to study organism survival during interplanetary flight conditions. Tardigrades, chosen for their radiation resistance, were part of this ambitious project.

Despite the setbacks faced by the 2012 Phobos Life Project, these investigations have provided valuable insights into tardigrades' potential as model organisms for astrobiological studies. Understanding their responses to space conditions not only advances our knowledge of extremophiles but also sheds light on the possibilities of life beyond Earth, contributing to the broader field of astrobiology and space exploration. (National Institutes of Health (.gov), 20)

Radiation tolerance:-?

Studies on radiation tolerance in Tardigrades indicate that exposure to c-radiation up to 1 kGy {k=kilo, Gy=grays.The gray (symbol: Gy) is?the unit of ionizing radiation dose?in the International System of Units (SI) } does not impact the survival of both desiccated and hydrated animals, with hydrated ones tolerating doses up to 5 kGy. For reference To cause human death within hours of radiation exposure, the dose needs to be very high, 10Gy or higher, while?4-5Gy will kill within 60 days. Similarly, the tardigrade Milnesium tardigradum, whether hydrated or desiccated, survives doses exceeding 5 kGy of c-radiation and up to 8 kGy of heavy ion radiation. Contrary to expectations, hydrated animals exhibit comparable or even better radiation tolerance than desiccated ones, challenging the notion that biochemical protectants associated with cryptobiosis are responsible. Instead, tardigrades seem to rely on efficient but unidentified mechanisms of DNA repair.

The BIOPAN 6/Foton-M3 mission in 2007, sponsored by the European Space Agency, involved experiments exposing cryptobiotic tardigrades to space conditions in low Earth orbit, including space vacuum and cosmic radiation. Although survival rates varied among tardigrade species and experimental setups, all studies unanimously concluded that tardigrades can endure the challenges of space. Notably, Milnesium tardigradum emerged as a particularly resistant species, with both embryos and adults tolerating space conditions. The comprehensive life history of this predatory tardigrade is well-documented in a study by Suzuki (2003).

(N. M?bjerg, 2011)

Glossary:-?

1.Cryptobiosis :-? a physiological state in which metabolic activity is reduced to an undetectable level without disappearing altogether. It is known in certain plant and animal groups adapted to survive periods of extremely dry conditions.

2.limno-terrestrial :- Being or inhabiting a moist terrestrial environment that is subject to periods of both immersion and desiccation.

3.Desiccation :- Desiccation is the state of extreme dryness, or the process of extreme drying. In biology and ecology, desiccation refers to?the drying out of a living organism. Microorganisms cannot grow and divide when desiccated, but can survive for certain periods of time, depending on their features.

4.Richtersius coronifer :- A species of Tardigrade.

5.Astrobiology :- the branch of biology concerned with the study of life on earth and in space.

6.Anhydrobiosis :- ?the phenomenon of the ability to enter a state of reversible ametabolism or suspended metabolism due to cell desiccation.

7.Anoxia:- Anoxia means?a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen".

8.Cyclomorphosis :- Cyclomorphosis is the name given to the?occurrence of cyclic or seasonal changes in the phenotype of an organism through?successive generations.

9.Desiccation :- the state of extreme dryness, or the process of extreme drying.

10.Extremophiles :- a microorganism, especially an archaean, that lives in conditions of extreme temperature, acidity, alkalinity, or chemical concentration.

Refrences :-?

1. https://www.researchgate.net/publication/49770874_Survival_in_extreme_environments-On_the_current_knowledge_of_adaptations_in_tardigrades

1. https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/Research/Tiny_animals_survive_exposure_to_space

1. https://www.americanscientist.org/article/tardigrades
2. https://www.nationalgeographic.com/animals/invertebrates/facts/tardigrades-water-bears#:~:text=Tardigrades%20belong%20to%20an%20elite,years%20without%20food%20or%20water.
3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5705745/
4. https://pubmed.ncbi.nlm.nih.gov/7997757/
5. https://www.nasa.gov/podcasts/houston-we-have-a-podcast/water-bears-in-space/
6. https://science.nasa.gov/biological-physical/investigations/cell-science-04/
7. https://astrobiology.com/2021/08/astronauts-initiate-tardigrade-experiment-on-iss.html