They have not eaten for the past 86 million years, but these deep-sea bacteria found on the bottom of the Pacific Ocean are not peckish either — as they don't really need food to survive, scientists say.

The hardy microbes, discovered when researchers drilled into a layer of soft red clay at the bottom of the Pacific Gyre, may have the world's slowest metabolism, with barely enough oxygen and nutrients needed to keep them alive. Believed to have remained untouched for almost 86 million years — well before dinosaurs went extinct — the microbes consume oxygen in quantities which are too small to be measured, the researchers said.

“We normally cannot see what rate they are working at,” Hans Roy, a geomicrobiologist at Aarhus University in Denmark, said of the microbes.

“It's so slow for us, it looked like suspended animation,” Roy was quoted as saying by the New York Times.

For their study, published in the journal Science, Dr Roy and his colleagues measured the oxygen concentration in layers of sediment gathered from the sea bottom in the North Pacific Gyre, off Hawaii, 100 feet below the surface.

They calculated how much oxygen should have diffused into each layer of the sediment. Any missing oxygen was likely to have been consumed by the microbes, Dr Roy said.

The deepest microbes that the researchers observed used just 0.001 femtomoles of oxygen per day; to put it another way, it would take 10 years for a microbe to consume the amount that a human inhales in a single breath.

“They are surviving on a minimum energy limit. The whole community seems to be hovering right at the hunger limit,” Dr Roy said.

The deep-sea microbes still largely remain a mystery to scientists, he added. As they are so slow-moving they are difficult to study.

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