The old microbes and the sea
The South Pacific Gyre is an aquatic nowhere. It is the spot in the sea that is farther from land than any other, so devoid of nutrients, life and even continental dust that it is considered “the deadest spot in the ocean,” said Steven D’Hondt, a geomicrobiologist at the University of Rhode Island.
Yet 6,000 metres beneath the surface of this watery desert, microscopic creatures have not only found a way to eke out a living — they have also managed to weather the inhospitality for many millions of years.
In a paper recently published in Nature Communications, D’Hondt and his colleagues describe the remarkable revival of a small population of microbes that may have spent the past 101.5 million years ensconced in a slumber under sediments deep below the gyre — only to be roused awake in the lab.
If confirmed, these microbes could be among the oldest living organisms ever found. Spawned during a time when the non-avian dinosaurs still stalked the
Earth, these hibernating cells might have rested as the continents creaked into their modern configuration, the globe’s first grasses emerged and our great ape lineage took its first steps toward walking upright.
Such longevity is unlikely, even mathematically impossible within the constraints of some models, said Yuki Morono, a microbiologist at the Japan Agency for Marine-Earth Science and Technology, or Jamstec, and an author of the study: “No theoretical microbiology can explain it. But we found it.”
Other scientists have unearthed snoozing microbes from harsh environments beneath the sea floor in the past. Crushed by kilometres of water and mud and starved of food, sunlight and warmth, cells must adapt or perish. Those that adapt can sometimes avoid death by simply teetering on the verge of it.
Scientists think that microbes will grind their metabolism to a near halt so they can make do with the meagre motes of food in their environment. Some in the field refer to this strategy as “the slow lane of life,” said Nagissa Mahmoudi, a geomicrobiologist at McGill University who wasn’t involved in the study.
“They’re not really thriving,” Mahmoudi said. “They’re just hanging on.”
But the relative rarity of such cells has made it tough to determine just how long such states of quasi-suspended animation can actually last.
So a team led by Fumio Inagaki, also of Jamstec, set sail into the southern Pacific Ocean in the fall of 2010 and drilled deep into its sediments. Over eons, mud settles in layers like a chronological stack of pancakes, with the newest additions closest to the sea floor; the oldest, about 75 metres under the ocean bottom, had been laid down about 101 million years before.
Even Morono was skeptical of finding life in the most ancient parts of the mucky, nutrient-poor cores the team extracted. Down there, bits of clay are crammed so tightly together that the spaces between them can’t even accommodate the full width of a bacterial cell.
“You are packed into the sediment and cannot move,” he said. “I cannot even imagine such a harsh environment as a human.”
But as he continued to sample backward in time, it became clear that there were microbes all the way down.
“This opens up a whole Pandora’s box for where we could find life elsewhere in the universe,” Mahmoudi said. “It seems everywhere we’ve gone, we’ve found life.”