Natures wonders: extremophiles in stratisphere (Introduction)

by David Turell @, Sunday, June 12, 2016, 14:43 (1346 days ago) @ David Turell

There are very hardy bugs at the extreme edges of our atmosphere:

"scientists are finding that a rich variety of life—archaea, bacteria, and single-celled eukaryotes—can thrive at high altitudes. In the troposphere, where day-to-day weather happens, each cubic meter of cloud contains on average tens of thousands of microbial cells. Even above the clouds in near space—as high as 250,000 feet, according to a 1978 Soviet study—rocket and balloon missions have collected hearty voyagers. “We're not just finding corpses that are blown up there and preserved,” says Brent Christner, a microbiologist at the University of Florida. “Some fraction of these organisms is still alive.”


"Depending on their size and aerodynamics, microbes can stay aloft in the atmosphere for days to weeks—long enough to jump a continent, or an ocean, in one go. Analyses of meteorological data, for instance, suggest that transatlantic winds carried fungal spores from West Africa to the Americas, spreading sugarcane and coffee leaf rusts to New World plantations in the 1970s. Bacteria kicked up by dust storms in Africa's drought-plagued Sahel appear to be making a similar leap to the Caribbean, where they are killing coral reefs. And in China, at the start of every growing season, spores causing wheat yellow rust migrate hundreds to thousands of miles from plants in the western provinces of Sichuan and Gansu to recolonize the country's main wheat belt farther north.


"No known organism can survive high altitudes indefinitely. Scientists estimate that even the fittest microbes probably last no longer than a week in the stratosphere, and around a couple of weeks in the troposphere. Eventually they “get fried by radiation,” says David J. Smith, a NASA microbiologist who led the October balloon mission testing the stamina of B. pumilus cells. As a result, some high-flying species may have evolved a method to get down fast: hijacking the weather.


"Microbial matter typically falls from the sky in rain or snow. To precipitate, clouds must grow ice crystals big enough to outweigh air, but pure water vapor won't normally freeze above -36 degrees Fahrenheit—unless it gets help from an “ice nucleator.” Most often, airborne particles such as salts or mineral dust provide this service. By supplying a seed around which water molecules can arrange themselves, a nucleator enables ice to form at temperatures up to 5 degrees. Some microorganisms produce proteins that catalyze the process in even warmer conditions, up to 28 degrees in a laboratory.


"If Earth's atmosphere is a microbial metro, it's an especially brutal one, and commuters have evolved various means to survive the trip. Some, like the B. pumilus cells in the NASA balloon, form endospores. “Sporulation is like hibernation for bacteria,” Smith says. “They shrivel down, dehydrate all of their innards, and wrap their DNA. They remain in that state until water and nutrients arrive, and then they flip the switch and germinate, and go on living.”


"The most successful cloud-squatters, Amato has found, are bacteria that spend their terrestrial lives on plants—no surprise, he says, considering that these species are well-adapted to life on the surface of a leaf, where light, temperature, and humidity change rapidly, as they do in a cloud. Many of these organisms have also evolved protections against UV radiation: pigments that act as sunscreens, for instance, or the ability to rapidly repair their own DNA.

"Where these widespread adaptations first arose is an open question. Did microbes hone their survival skills on the ground and then use them to take to the skies? Or vice versa? Smith, for one, argues that the arduous conditions of the upper atmosphere likely provided a selective pressure that drove terrestrial life to be as robust as it is. “Think about trillions upon trillions of tiny cells continuously passing through the Earth's deadly upper atmosphere for billions of years,” he says. “In that framework, evolved resistance to environmental extremes seems almost inevitable.”


"How Earth life might get to other planets is a matter of much debate. Airborne cells can't reach escape velocities great enough to break free of Earth's gravitational pull. Nor have scientists come up with a convincing explanation of how they would survive the long transport times and lethal radiation levels in deep space. But that hasn't stopped astrobiologists from musing about panspermia, the hypothesis that life spreads throughout the universe via meteors and other cosmic vehicles—like, say, spacecraft.

"For NASA, this is a very real, and troubling, possibility. The agency has identified hundreds of bacterial strains like B. pumilus that have outlived spacecraft sterilization procedures such as peroxide baths, heat shock, and UV radiation. What would happen if these or other hardy microbes stowed away in a dark crevice on a lander, or latched on as it passed through Earth's atmosphere?"

Comment: These organisms show how inventive life's adaptations can be. Our oft discussed inventive mechanism must exist, not yet found.

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