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Deep-Sea Microbes Exert the Least Amount of Energy Possible to Survive

Giving a whole new meaning to doing the “bare minimum”

Alvin, a remotely operated submersible, drills for samples of the deep sea floor in 2014. (Geoff Wheat, NSF OCE 1130146, and the National Deep Submergence Facility)
smithsonianmag.com

Some 200 to 600 octillion microbes live deep underneath the seafloor, where they’re subject to intense pressure and have only rocks, methane and the occasional bit of oxygen for sustenance.

Simply surviving in these conditions is a feat. New research suggests that the microbes make it work by expending the least possible amount of energy needed to survive—less energy than was previously known to support life on Earth.

The paper, published last week in Science Advances, “call[s] into question the power limit to life,” the authors write.

Scientists used data from sediment samples collected by drilling deep into the ocean floor, reports Layal Liverpool for New Scientist. The team, led by researchers with the Queen Mary University of London, used computer models to analyze the rate of biological and chemical reactions in subsurface microbes and predict the consumption rates of individual microbes, per a statement.

“When we think about the nature of life on Earth, we tend to think about the plants, animals, microscopic algae, and bacteria that thrive on Earth’s surface and within its oceans—constantly active, growing and reproducing,” says James Bradley, an environmental scientist with Queen Mary University of London and an author on the paper, in the statement.

“Yet here we show that an entire biosphere of microorganisms—as many cells as are contained in all of Earth’s soils or oceans, have barely enough energy to survive,” continues Bradley. “Many of them are simply existing in a mostly inactive state—not growing, not dividing, and not evolving.”

Humans, Bradley points out, require about 100 joules of energy each second to sustain basic functions—about 100 watts of power, similar to the amount needed to power a ceiling fan. By comparison, “[w]e calculate that the average microbe trapped in deep ocean sediments survives on fifty-billion-billion times less energy than a human,” the researcher notes.

Their low energy consumption allows the microbes to survive buried deep underground for millions of years, per New Scientist. As Bradley tells Becky Ferreira for Vice, the team suspects that these microbes are not reproducing. Rather, they might be the surviving remainders of microbe populations that lived in Earth’s shallow coasts, thousands of years ago, per the statement.

Although one might assume that a hostile habitat so far beneath the Earth’s surface would be inhabitable, the region actually boasts an expansive network of microbes, reports Vice. As Hannah Waters reported for Smithsonian magazine in 2013, this “deep biosphere” might be the largest ecosystem on the planet, and could be to millions more undiscovered forms of microbial life.

Researchers say that this study could aid astronomers as they search for life on distant planets, by providing a baseline measure of the energy needed to sustain a form of life. “Previous studies of life in the subseafloor […] focused predominantly on who’s there, and how much of it is there. Now we’re digging deeper into ecological questions: what is it doing, and how fast is it doing it?” says Jan Amend, a scientist with the University of Southern California and study co-author, in the statement.

“Understanding the power limits of life establishes an essential baseline for microbial life on Earth and elsewhere,” Amend concludes.

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