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Deep-sea microbes survive on less energy than we thought possible

Taking samples from the sea floor

Geoff Wheat, NSF OCE 1130146, and the National Deep Submergence Facility

Deep-sea microbes can survive on less energy than previously thought necessary for any living thing, potentially changing the definition of life as we know it.

“[This] broadens the range of environments we might consider plausible to search for life,” says James Bradley at Queen Mary University of London.

Bradley and his colleagues used data from sediment samples collected from beneath the sea floor to determine the rate of energy use by the microorganisms that live there.

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Using a model that considered various aspects of the habitat, including the rate at which organic carbon is degraded, the availability of oxygen and the number of microorganisms present, Bradley and his team calculated the rate of energy use per microbial cell.

They found that this value was 100 times lower than that previously thought to be the limit for life. A few cells survived on less than a zeptowatt of power, or 10^-21 watts.

Scientists have previously estimated the lower energy limit for life by growing microorganisms in the laboratory and then starving them of nutrients to determine the limit for survival.

But Bradley says that while these experiments provide important insights, they don’t fully represent the range of natural environments that microorganisms inhabit in the real world, including the unique environment beneath the sea floor.

Because of their extremely low rate of energy consumption, the microbes – mainly bacteria and archaea – can survive buried for millions of years. “[This shows] that you need less energy to sustain life over long time scales and that increases the possibility of places which we can go to search for life on other planets,” says Bradley.

There may once have been abundant liquid water on the surface of Mars. If there was life there at the time, then these new findings raise the possibility that there could be remnants of that life subsisting, waiting for the environment to become habitable again, says Bradley.

“I don’t think that we have a good understanding yet of the mechanisms by which they survive in this incredibly low energy state for millions of years,” says Bradley. “Possibly it’s something to do with their ability to reduce their metabolic rate… and to enter into a kind of zombie-like state.”

Journal reference: Science Advances, DOI: 10.1126/sciadv.eaba0697

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