Survival in the Vacuum of Space - Tardigrades
Absolute zero near temperature, full vacuum environment, and cosmic radiation... Challenging conditions for a living thing.
When a person goes unprotected to space, it can cause the freezing within seconds, the collapse of lungs, and the conversion of all the oxygen in blood into gas. The situation is grave for complex creatures like us, but an extraordinary species can survive for days without harm in the vacuum of space. Tardigrades...
Today, 1000 different Tardigrade species connected to the Tardigrada branch are defined. Their habitats are so broad that it is possible to encounter these species everywhere from the Himalayas (+6000 meters) to the deep seas (-4000 meters), to the equatorial poles. At the same time, these creatures can be seen in more moderate environments such as lakes, fresh water sources, stone walls, and roofs. These species, which usually live in moist environments, can survive in low humidity environments.
The popularities of the Tardigrade are also due to these extreme features of the environments that they live in. They can survive in situations that can kill many living things. While it can survive temperatures close to absolute zero (-273 ° C), it can resist 1,000 times more radiation than most animals can withstand.
Little Giant!
The Tardigrades also referred to as the "water bears," are aquatic, microscopic dimensional and 8-legged at the same time. The species discovered by Johann August Ephraim Goeze in 1773, took the nickname "Kleiner Wasser Bär" because of its legs despite living in the water. Biologist Lazzaro Spallanzani called it Tardigrada, meaning "Slow Walker" after three years its discovery. Adults who can easily see on light microscopes can reach 1.5 mm in size, with a minimum of 0.1 mm. Larvas sizes are only 0.05 millimeters.
The Tardigrades have four pairs of legs that connected a little chubby, attached to a cylindrical body. If we do not count the head part, the body with four sections, each section has no joints and four clawed legs. The clawed legs provide grip on the sand grains or plant surfaces. The outer layer (cuticle) made of chitin is periodically renewed.
Structural Features
Another interesting feature of the Tardigrades is that they are "eutelic." This means that the number of cells that individuals have at birth is constant throughout their lives. All the same kind of individuals have the same amount of cells. While some species contain up to 40,000 cells, others have fewer cells. (Another example of "eutelic" organism is roundworms.) Their proliferation can be either sexual or parthenogenesis. So a female egg can form an individual without fertilization.
The Tardigrades do not have respiratory organs. Gas exchange is carried out over the entire body surface. The mouth part has a sharp, knife-like structure called "stylet." They can consume plant cells, algae, small invertebrates and even other Tardigrades with these pieces.
What destroys them? Nothing!
Observations on these creatures show that these species can survive in hot springs, at the tops of the Himalayas, under solid ice layers, and in oceanic sediments. Now let's take a look at these extreme environmental conditions that the Tardigrades can tolerate, then let's examine what they owe their resistance to and what mechanisms they owe.
Temperature
Tardigrades can survive for minutes at a temperature of 151 ° C. Likewise, and it can live for days without being damaged at -200 ° C. They can stay alive for a few minutes at 1 ° C above absolute zero (-272 ° C).
Pressure
These species can survive under extremely low pressure (in the vacuum). Similarly, they do not lose their vitality at pressures as high as 1200 times that of the atmospheric pressure. In previous space experiments, the Tardigrades exposed directly to space vacuum for ten days were seen to be alive when they were brought back to Earth. It is known that some types of Tardigrades can resist on 6000 times of atmospheric pressure. This pressure is about six times the pressure at the deepest point of the ocean floor (Mariana Pit).
Lack of Water
The Tardigrades survive for ten years in a dry environment.
Radiation
The Tardigrades can survive in deadly radiation levels that dangerous for most living things. It has been observed that radiation levels such as 5000 Gy and 6200 Gy survive. If we want to make a comparison, it is enough to say that 10 Gy is fatal for humans. The Tardigrades, exposed to cosmic radiation during the Foton-M3 space flight, were able to survive more than 68% survivors.
Environmental Toxins
Tardigrades can enter the phase, called chemobiosis, and have high resistance to environmental toxins. However, laboratory work carried out on this subject is still ongoing.
Well, How Does That Work?
How do the Tardigrades hold up to these extreme environments? First of all, it's worth pointing out, in the extreme conditions above, the Tardigrades are not actively alive. Instead, they go to a semi-dead stage called Cryptobiosis. In this phase, similar to winter sleep, the metabolic rate is almost zero. Programmable water loss is one of the most apparent changes in the cryptobiosis process.
The water content of the Tardigrades bodies is reduced from 85% to 3% at low temperatures. The body water is frozen at low temperatures to prevent damages in this way. (The most significant damage during freezing is that the water in the cell crystallizes and gives physical damage to the cell membranes.) The Tardigrades throw water out of their cells, preventing possible crystallization. This resistance mechanism is also called Cryobiosis.
Water loss also plays a role in radiation resistance. Despite studies on this subject, it is suggested that the primary strength comes from low-level water in the body. The reactive molecules that radiation brings into the cell do not react in the anhydrous environment. Low amounts of water reduce the risk of "harmful" reactions that may occur.
When Tardigrades put all the water in their bodies, they get a form called "tun." In this state, the metabolism works at less than 0.01% of the average level. The water level in their bodies can go down to 1% of normal.
Future Work on Tardigrades
Work on Cryptobiosis can provide the Tardigrades' "survival skills" to other organisms as well. Studies about on this subject have shown some improvements in vaccine technology. It is possible to dry without killing some pathogens with the Cryptobiosis feature. At this point, the "attenuated organisms" of the vaccine content can be stored dry. Similar technologies can be used in the future to hide sperm, seeds, blood and different foods. Maybe freezing anesthetize may be possible during interplanetary journeys. Who knows?
