Projects: LIFE Experiment: Phobos
Eukaryotea: Fungus, "Water Bears" and More
by Amir Alexander
Brewers' Yeast
Scientifically known as Saccharomyces cerevisiae, "Brewers Yeast" or "Bakers Yeast" is the organism used in the brewing of beer and bread baking.
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In addition to bacteria and archaea,
our LIFE biomodule will carry eukarryotea. Eukaryotea are organisms
whose cells contain a nucleus and other organelles. Many Eukaryote species
are single celled, similar to bacteria and archaea, but some are complex
multi-celled organisms. In fact, most of the creatures we normally think
of as living beings – animals,
plants, and fungi, everything from amoebas to elephants – are eukaryotea.
Saccharomyces cerevisiae
The only fungus selected for the trip to Phobos is known to scientists
as Saccharomyces cerevisiae, but it has many more popular nicknames:
Brewers Yeast, Bakers Yeast, Ale yeast, and so on. It is the very same
fungus that has been used for millennia for baking bread and fermenting
beer, though for most of this time humans were not aware that these processes
involved living organisms. That discovery was made only in the late 19th
century by the French chemist and microbiologist Louis Pasteur.
Because of its central role in food production, Saccharomyces cerevisiae is one of the most studied organisms and one of the best known to scientists. It is a model organism, used in a wide array of biological experiments, and just as Bacillus subtilis is the gold standard of Gram-positive bacteria research, Saccharomyces cerevisiae plays the same role for eukaryotes.
Arabidopsis thaliana
The only plant included in the LIFE experiment is known scientifically Arabidopsis thaliana and more commonly as the "thale cress" or "mouse-ear cress." An unassuming weed with a small flower, it was originally native to Europe and central Asia but has now spread world-wide. Thanks to its relatively small genome, its short life-cycle, and the ease with which it can be genetically manipulated, Arabidopsis thaliana has become a favorite of scientists and is now, according to Warmflash, the "Gold Standard" of plant research. Furthermore, Arabidopsis thaliana had already been to interplanetary space as part of the Biostack experiment that flew to the Moon on board Apollo 16 and 17. Comparing these results of the short trip to the Moon to the effects of the long trip to Phobos can offer scientists insights into plant adaptability to conditions of interplanetary space.
Arabidopsis thaliana
This common plant, known also as the "Thale Cress" and "Mouse-Ear Cress," is a model organism used extensively in scientific research. Its seeds will be included among the organisms sent to Phobos and back in the LIFE experiment.
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Tardigrades
Finally, the LIFE experiment will also take on board a sample of true animals, known technically as "tardigrades" and popularly by the more endearing name "water bears." Tardigrades are tiny – the largest adults reach a length of 1.5 millimeters, and the smallest are less than one tenth of that. Their bodies are composed of four segments, each with two legs punctuated by claws at the end. Most significantly, tardigrades are everywhere: they can be found from the high Himalayas to the deepest sea, from the polar regions to the equator, as well as in more hospitable environments such as rivers, ponds, and sand-dunes.
Tardigrades can inhabit such diverse settings because they are extremophiles, capable of surviving in extraordinarily hostile conditions. They can be heated to over 150 degrees Celsius for several minutes, or chilled to just a few degrees above absolute zero, and live. They can withstand both the pressure of 6000 atmospheres and a vacuum, and have even been exposed to space in low Earth orbit and survived. Their resistance to radiation is comparable to that of Deinococcus radiodurans, and they are able to withstand over 500 times the level of radiation that would kill a human. All of which is to say that it is very, very hard to kill a water bear.
The secret to tardigrades' mind-boggling survivability is their ability to enter a state of "cryptobiosis," or suspended animation, when environmental conditions turn hostile. In this condition their water content is drained to 1% of normal, and their metabolism reduced to 0.01% of its normal rate. Tardigrades can survive in this state for nearly a decade and still “return to life” as viable animals when conditions improve.
Water Bear
Known scientifically as "tardigrades," these creatures range in size from 0.1 to 1.5 millimeters. Credit: Rick Gillis and Roger J. Haro Department of Biology University of Wisconsin - La Crosse.
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All this makes water bears ideal representatives of the animal kingdom for the LIFE experiment. If any animals can survive a long journey through space, then tardigrades can. After much consideration, four different samples of tardigrades were packed inside the LIFE capsule for the long journey: 30 specimens of the species Richtersius coronifer; 20 eggs of the same species; 20 specimens of Milnesium tardigradum; and 20 specimens of Echiniscus testudo.
We already know that these creatures can be subjected to extremely low temperatures, microgravity, and high radiation, and live. But can they be subjected to all three at the same time for nearly three years – as they will be on the round-trip to Phobos – and yet survive? Scientists do not know, but if all goes well they will soon find out.
Colony
The final passengers to Phobos in the LIFE module are the microbial residents
of grains of soil from the Negev desert in Israel, provided by Russian scientists
on the team. The rational behind this is that a living colony of interdependent
organisms has been shown to be hardier and more resistant to hostile environmental
conditions than a single organism on its own. When the grains return from
their long sojourn in space, scientists will be able to compare any surviving
organisms with identical control samples that were left on Earth.
Read more about the bacteria and archaea in
the LIFE biomodule.
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