Bacterial survival in salty antifreeze raises hope for life on Mars and icy moons

Bacterial survival in salty antifreeze raises hope for life on Mars and icy moons
Jets spewing salty water vapor and ice from Saturn’s moon Enceladus. Could the mix of water, salt and temperature enable life to exist there? Credit: NASA/JPL–Caltech/Space Science Institute

New research by a trans-Atlantic team of scientists suggests that bacteria could survive in briny chemicals that exist on Mars, Enceladus, Europa, Pluto and possibly elsewhere.

The discovery of plumes and subsurface oceans on Jupiter's moon Europa, organic materials on Mars, and the likelihood of hydrothermal vents in the oceans of Saturn's moon Enceladus, inches humanity closer to discovering life elsewhere. Such life would have to withstand extreme environments, and previous studies indicate that various types of can.

Liquid oceans on some bodies far from the Sun have lower freezing points because of chemicals and salts that amount to antifreeze, so microbial life would have to survive both the temperatures and the elements. To zoom in on parameters for microbial survivability, researchers from the Technical University of Berlin, Tufts University, Imperial College London, and Washington State University conducted tests with Planococcus halocryophilus, a bacteria found in the Arctic permafrost.

They subjected the bacteria to sodium, magnesium and calcium chloride cocktails, as well as solutions of , which is a chemical compound that may help Mars sustain liquid water during the summer. Lead author Jacob Heinz, of the Technical University of Berlin's Center of Astronomy and Astrophysics, says that the researchers expanded beyond the conventional sodium chloride solution because "there's much more than that on Mars."

Toxic to life

Since perchlorates are toxic in large concentrations, researchers wanted to determine whether, how much and at what concentrations they might inhibit bacterial survivability. Survival rates for bacteria in perchlorate were far lower than in all the other solutions, although at temperatures as low as –30 degrees Celsius (–22 degrees Fahrenheit), the rates were slightly better.

Heinz explains that the lowest freezing point depression – the extent to which a solute can lower a solution's freezing temperature – for perchlorate requires roughly 50 percent of the mass of the total solution, which is incredibly high compared to the freezing-point depression of other chlorides. Given its toxicity, the low survivability of bacteria in concentrated perchlorate solutions isn't surprising.

Bacterial survival in salty antifreeze raises hope for life on Mars and icy moons
The underground ocean on Jupiter’s moon Europa is suspected to be rich in salt and, on the occasions that the salty water reaches the surface, it is exposed to high-energy particles trapped in Jupiter’s radiation belts that turn the salts deposited on the surface from white to a yellowish brown, as seen by previous space missions. Credit: NASA/JPL–Caltech

Does that mean that Mars can't support microbial life? According to Heinz, life is still a possibility there. The presence of perchlorate "wouldn't preclude life on Mars or elsewhere," he says. "Bacteria in ten percent mass perchlorate solutions can still grow." Mars's surface soil contains less than one weight percent of perchlorate, but Heinz points out that salt concentrations in solutions are different than those in soil.

Adapted to survive

Liquid perchlorate solutions can also be diluted to increase the bacteria's ability to survive, though a balance between concentration and temperature would have to be maintained.

Theresa Fisher, a Ph.D. student at Arizona State University's School of Earth and Space Exploration who focuses on microbial ecology and planetary habitability, agrees that the study's results don't rule out bacterial survival on Mars – in fact, perhaps the opposite.

Places such as the Atacama Desert (the world's driest environment) in Chile and parts of Antarctica have relatively high perchlorate levels, Fisher tells Astrobiology Magazine.

"I'd be surprised if microbes haven't evolved a way to deal with that toxicity," she says.

Generally, colder temperatures boost microbial survivability, but temperature isn't a "one-size-fits-all" factor– the type of microbe and the composition of the chemical solution also determine the sweet spot for survivability. The researchers found that bacteria in a sodium chloride (NaCl) solution died within two weeks at room temperature. At four degrees Celsius, survival increased, and once temperatures hit –15 degrees Celsius (5 degrees Fahrenheit), almost all the bacteria survived. NaCl has a higher freezing point (–21 degrees Celsius/–5.8 degrees Fahrenheit) than the other salts; bacteria in the magnesium and calcium-chloride solutions had high survival rates at –30 degrees Celsius (–22 degrees Fahrenheit).

Bacterial survival in salty antifreeze raises hope for life on Mars and icy moons
The survival rates of bacteria in various types of salt – sodium chloride (NaCl), magnesium chloride (MgCl2) and calcium chloride (CaCl2). In general, the cooler the temperature, the longer they survived. Credit: J. Heinz et al

This isn't surprising because "all reactions, including those that kill cells, are slower at lower temperatures," says Heinz, "but bacterial survivability didn't increase much at lower temperatures in the perchlorate , whereas lower temperatures in calcium chloride solutions yielded a marked increase in survivability."

Results also varied between the three more conventional saline solvents. Bacteria in calcium chloride (CaCl2) had significantly lower survival rates than those in sodium chloride (NaCl) and magnesium chloride (MgCl2) between 4 and 25 degrees Celsius, but lower temperatures boosted survival in all three.

Researchers subjected the bacteria to numerous freeze/thaw cycles ranging from 25 degrees Celsius (77 degrees Fahrenheit) to –50 degrees Celsius (–58 degrees Fahrenheit). Mars can undergo some pretty dramatic surface temperature changes, both diurnal and seasonal, depending on the location on the planet says Heinz. The average on Mars is roughly –60 degrees Celsius (–76 degrees Fahrenheit), with temperatures at the poles dropping to –125 degrees Celsius (–193 degrees Fahrenheit). Consequently, bacteria need to be able to endure extreme fluctuations in order to survive.

Generally, saltier solutions improved freeze/thaw . According to Fisher, "bacteria, when stressed, have shock responses. They manufacture specific proteins that help them adjust, survive, and cope with detrimental environments." Adding 10 percent decreased the microbial death rate from 20 percent to 7 percent and increased the number of freeze/thaw cycles the bacteria could sustain from 70 to 200. Bacteria manufacture stabilizing proteins as a shock response to severe environments, Fisher explains, "but there are only so many shock proteins bacteria can produce."

Survival versus growth

While the study provides insight into extraterrestrial microbial possibilities, Heinz emphasizes the difference between surviving and thriving. Just because bacteria subsist in certain conditions doesn't mean they actually grow. Heinz is currently working on another study to determine how different concentrations of salts across different temperatures affect bacterial propagation.

"Survival versus growth is a really important distinction," Fisher affirms, "but life still manages to surprise us. Some bacteria can not only survive in low temperatures, but require them to metabolize and thrive. We should try to be unbiased in assuming what's necessary for an organism to thrive, not just survive."

Studies that explore various salt solutions, concentrations, and temperatures help scientists focus the search for life, or at least not rule out possibilities, such as microbial survival in toxic perchlorate. Other variables affect the search for life, such as a bacteria's ability to withstand radiation or extreme atmospheric pressure. There may even be factors we don't know about yet, but with each study, there's one fewer haystack to search.

Explore further

Mimetic Martian water is under pressure

This story is republished courtesy of NASA's Astrobiology Magazine. Explore the Earth and beyond at .

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Jul 06, 2018
Europe Moon has an average temperature of -171.15 ° C, Pluto -229 ° C etc.
https://en.wikipe...e_glycol Propylene glycol -74 °C,
https://en.wikipe...Methanol Methanol -97,6 ° C,
https://en.wikipe...e_glycol Ethylene_glycol -12,9 ° C,
https://en.wikipe.../Ethanol Ethanol -114,14 ± 0,03 [2] ° C,
https://en.wikipe..._alcohol Isopropyl_alcohol -89 ° C,
https://en.wikipe...-Butanol N-Butanol -89,8 ° C etc.
In what world they live these authors?

Jul 06, 2018
@wduckss - While the surfaces of Europa and Pluto are too cold for such antifreezes to keep water liquid, Europa and Pluto are warmer deeper down.

Think of our own world. The surface averages just warm enough for liquid water, but deeper down it is hot enough for liquid rock!

Jul 07, 2018
The surface is full of evidence, it should go deeper into ignorance.
What process do you have in a fantasy that warms the space body, small green which fire the fire?
Uranus is the mass of a large, completely cold. It emits only 1.06% more heat than received heat from the Sun. Let this be the starting point for your answer (comment).

How is created. heat. you can learn in: http://www.svemir...-(stars)
Clarification look at:

Jul 07, 2018
Uranus? You asked about Europa and Pluto, which the article mentions...
Europa's interior is heated primarily by tidal flexing, with some heat from radioactive decay.

Pluto has the same two sources, but with the mutual tidal lock to and the near-circular orbit of the only major moon, tidal heating should be pretty low so radioactive decay is probably the dominant source (but research is ongoing).

But how much heat do you think that it takes to warm something enough to keep salty brine slushy? For example, Earth's internal heating is only ~0.03% of what we receive from the sun, and that melts rock.

Smaller bodies heat less due to both more surface per volume and a shorter distance for for the temperature gradient to accumulate over, but high-salt brine is a lot easier to keep liquid than rock is.

Use you wiki searches on Europa and Pluto!

Jul 08, 2018
Uranus is (in the example) because of the size of the mass. Uranus is a basic proof that there is no radioactive heating due to decomposition.
The problem with Europe is the lack of O2. Europe also has no H2, no H2 in the atmosphere.
The atmosphere is formed
Everything else is a story without coverage (evidence) .

Jul 08, 2018
What's really interesting here is that under this theory biogenesis didn't occur on Earth but instead someplace else.

Jul 08, 2018
What's really interesting here is that under this theory biogenesis didn't occur on Earth but instead someplace else.

Personally I don't buy this biogenesis didn't occur on Earth but somewhere else and then was transported to Earth.
It doesn't help to solve any mystery because it still had to occur SOMEWHERE and, since it still had to occur somewhere ANYWAY, why not on Earth? This is the simpler hypothesis and I think that, with all else being equal, the simplest hypothesis is more likely (Occam's razor) and to say it occurred elsewhere and then was transported to Earth is more complex because you have the extra assumption that it was transported to Earth (that you can 'shave off' with Occam's razor)

Jul 08, 2018
Really depends on how likely each one is.
In the end we'll eventually figure it out when life on other bodies is discovered. It shouldn't look the same everywhere on a basic level (and even if it does for some reason then the handedness of molecules wil be a clue, since it's totally random whether life will prefer left or right chirality..but once it latches upon one that is locked in.)

It could be that life is rare to the point where all life in one solar system is likely from the same stock. It could be so easy to start off that everywhere you go it's different. With one sample point in our current inventory we just don't know (although given that life started off very early after Earth cooled that seems to suggest that life can start off easily)

Jul 08, 2018
a_p I can agree with most of what you said as reasonable conjecture.

However: ....(although given that life started off very early after Earth cooled that seems to suggest that life can start off easily)....

That leaves out the niggling little detail that it took Achaean micro-organisms BILLIONS of years to achieve the status of slime and begin building stromatolites.

As the other failed planets in our Solar System vividly display. There are a whole lot of different things that can go wrong with the process of establishing a Living World.

Jul 08, 2018
Lower or upper limit at which stops any possibility of the formation of life is -130 ° C.
Europe Moon has a mean temperature of -171.15 ° C, Pluto -229 ° C etc.
Or, give up such articles, or publish official data that the temperatures announced by official science lie as authors know better than published measurements (evidence).

Jul 08, 2018
@wduckss: Let's check whether Uranus proves that there is no decay heat.

At 4 times earth's diameter Uranus has 16 times the surface, but at 20 A.U. from the sun it receives 1/400 the heat per area, so it totals 16/400 = 1/25 as much solar heat as earth.

The best estimate is the Uranus emits 1.06 times the heat (not 1.06% more) that it receives. So that extra 6% of Uranus solar heat would be 6%/25 = 0.24% or earth's solar heat. The earth only emits 0.03% of more than its solar heat, so Uranus emits roughly 8 times MORE extra heat than earth emits.

Ice doesn't release much decay heat, so that means that even if Uranus's core is as radioactive as earth's, emitting 1.06 times its solar heat would allow a core up to 8 times the mass of earth's core. However estimates of Uranus's core range from half an earth mass to 4x an earth mass.

So Uranus emits MORE extra heat than just radioactive decay, contradicting your claim.

Jul 08, 2018

Europe Moon has a mean temperature of -171.15 ° C, Pluto -229 ° C etc.

No, those are the mean temperatures of the SURFACES of Europa and Pluto, not the whole bodies.
I have not seen anyone suggest that their SURFACES have life (or even liquid water).

Interiors can be hotter than surfaces. Earth's surface averages around 15C, yet underground it is hot enough for molten rock.

Jul 08, 2018
That leaves out the niggling little detail that it took Achaean micro-organisms BILLIONS of years to achieve the status of slime and begin building stromatolites.

Not surprising. Evolution only works when there is selection pressure. On an uninhabited world there is no selection pressure once something gets going...until that something makes selection pressure for its own kind by sheer population or pollutes the environment (e.g. by excreting oxygen) to where adaptation is necessary (either into something that can use these waste products or as something that can now feast on the ubiquitous organic matter)

But that does not invalidate that point that the first organisms started off very early - which in itself sugests life starts off rather easily. it could well be that on other bodies in the solar system (Io, Enceladus Ganymede, Callisto, Titan, Europa ..) are just still in the initial growth phase. We won't know unless we take a look.

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