Spacey lichens, fungi, and tardigrades are helping scientists understand what life forms to look for on Mars. All these organisms have survived both open space and Mars-like conditions. Tardigrades were space explorers before lichens and fungi, and now scientists are learning why this animal can survive outside earth’s atmosphere.
Lichens and fungi are the most recent space travelers. They spent 18 months on the outside of the International Space Station (ISS) in an experimental research unit called EXPOSE-E that holds organisms in open space environment. The study is part of the Lichens and Fungi Experiment — LIFE. The fungi were collected from the Antarctic McMurdo Dry Valleys, considered the most Martian-like environment on earth. The lichens came from mountains in Spain and the Austrian Alps. Some fungi and lichens were exposed to open space conditions, others experienced Mars-like conditions.
More specifically, this is an atmosphere with 95% CO2, 1.6% argon, 0.15% oxygen, 2.7% nitrogen and 370 parts per million of H2O; and a pressure of 1,000 pascals. Through optical filters, samples were subjected to ultra-violet radiation as if on Mars (higher than 200 nanometres) and others to lower radiation, including separate control samples.
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After 18 months hanging around on the outside of the ISS they were studied. Among the fungi, more than 60 percent of the cells survived and their cellular DNA was intact. Lichens also handled Mars-like conditions just fine.
Another range of samples (both lichens and fungi) was subjected to an extreme space environment [….] The effect of the impact of ultra-violet extraterrestrial radiation on half of the samples was also examined [….]
After the year-and-a-half-long voyage, and the beginning of the experiment on Earth, the two species of lichens ‘exposed to Mars’ showed double the metabolic activity of those that had been subjected to space conditions, even reaching 80% more in the case of the species Xanthoria elegant [….]
The results showed subdued photosynthetic activity or viability in the lichens exposed to the harsh conditions of space (2.5% of samples), similar to that presented by the fungal cells (4.11%). In this space environment, 35% of fungal cells were also seen to have kept their membranes intact, a further sign of the resistance of Antarctic fungi.
The first earth animals to survive open space were tardigrades, tiny invertebrate animals.
Water bears, also known as tardigrades, are very small, segmented animals. The largest species is just over one millimetre in length. Water bears live in temporary ponds and droplets of water in soil and on moist plants. They are known to survive under conditions that would kill most organisms – they can withstand temperatures ranging from -272 deg C to +150 deg C, they can be without water for a period of 10 years, and they are extremely resistant to radiation.
Since their space survival, researchers have investigated how they accomplish this and recently announced they suspect it is due to horizontal gene transfer. It’s as if when they fall sleep their DNA shatters, and when they wake up any DNA damaged during sleep is auto-repaired, plus takes in bits of whatever foreign DNA is nearby. That last part is the horizontal gene transfer.
...the tardigrade species Hypsibius dujardini acquires about 6,000 foreign genes primarily from bacteria, but also from plants, fungi, and archaea. The team believes this transfer occurs when tardigrades reemerge from their “tun” state. Depending on environmental conditions, tardigrades go into a kind of hibernation, suspending their metabolism and remaining in a dehydrated state for up to ten years. During this desiccation process, the tardigrade’s DNA seems to break into tiny pieces. When the cell rehydrates, the cell’s membrane and nucleus, where the DNA resides, becomes temporarily leaky and DNA and other large molecules can pass through easily. Tardigrades can not only repair their own damaged DNA as the cell rehydrates, but they can also incorporate foreign DNA in the process, creating a mosaic of genes that come from different species.
Research such as these with lichen, fungi and tardigrades help scientists understand how to look for life on Mars.
The results help to assess the survival ability and long-term stability of microorganisms and bioindicators on the surface of Mars, information which becomes fundamental and relevant for future experiments centred around the search for life on the red planet….
Perhaps lichen, fungi and tardigrades will be the first earthlings on Mars. Or are they the first Martians on earth?
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