The South Pacific Gyre is an aquatic nowhere. It’s the spot in the sea that’s farther from land than any other, so devoid of nutrients, life and even continental dust that it’s considered “the deadest spot in the ocean,” said Steven D’Hondt, a geomicrobiologist at the University of Rhode Island.
Yet some 20,000 feet beneath the surface of this watery desert, microscopic creatures have not only found a way to eke out a living — they’ve also managed to weather the inhospitality for many millions of years.
In a paper published Tuesday 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 seafloor in the past. Crushed by miles 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 meager 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 seafloor; the oldest, some 250 feet under the ocean bottom, had been laid down about 101.5 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.
The work wasn’t easy. To avoid discombobulating the fragile cells too much, Morono tried to replicate their home environment as best he could. That meant spending up to 10 hours a day working in a room chilled to below 50 degrees Fahrenheit, bundled from head to toe, as he plied the bugs with bits of chemically labeled food.
Morono expected that after thousands, if not millions, of years stuck in the mud, the microbes would be slow to rise. But within just a few days, some of the groggy germs had started to divide. For nearly two years, the researchers watched their specimens grow; 557 days later, many communities of the teeny troopers were still chugging along.
The microbes’ newfound vivacity hints that for millions of years, they were “just kind of waiting for conditions to improve,” said Virginia Edgcomb, a geomicrobiologist at Woods Hole Oceanographic Institution who wasn’t involved in the study.
It’s hard to determine the age of individual cells, Edgcomb added. Some may be as old as the sediments they once sat in; others may be the progeny of these ancients. Given how spare the microbes’ diets probably were, D’Hondt suspects that reproduction was probably rare. That makes it all the more remarkable that, even after spending millions of years just barely ticking along, the cells were game to “sit up and party on,” he said.
Even older microbes could still be in yet-untested seafloor sediments, which can be up to 200 million years in age. Future-minded scientists could find these stalwart specimens useful — including those involved in the search for extraterrestrial life.
“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.”