Microbes, however, have no trouble getting creative—and maybe a little macabre, according to a recent study published in the journal Geology. Starved of proper sustenance, ancient single-celled residents of the Dead Sea might have consumed the corpses of other types of microbes to survive.
And munching on the bodies of fallen brethren might have served up a double dose of success in this inhospitably salty lake: In addition to supplying convenient food, the dead might have also indirectly gifted grave-robbing microbes with water.
The findings, which catalog the habits of bacteria that lived more than 100,000 years ago, don’t necessarily hold true in modern times. But they showcase the remarkable resilience of creatures weathering conditions possibly even more unforgiving than those of today’s Dead Sea—and might even inform the ongoing search for extraterrestrial life.
“This is yet another example of how extraordinarily innovative microbes are,” says Mary Voytek, an astrobiologist and microbial ecologist at NASA who was not involved in the study. “It’s a unique, clever solution to what organisms typically do, which is come up with ways to access the things they need.”
By weight, ocean water is about 3.5 percent salt. Multiply that by 10, and you’ve got the suffocating salinity of the Dead Sea. “In this environment, the high salinity and lack of food are pretty extreme,” says JoAnn Holloway, a biogeochemist at the United States Geological Survey who was not involved in the study. “That’s going to limit who can live here.”
If any critters were up to the challenge, though, it would be archaea—a group of single-celled organisms distinct from bacteria with an impressive set of survival skills. These stalwart microbes have been found lounging in many harsh environments that host little, if any, other life, from volcanic hot springs to frigid subterranean Antarctic lakes.
Salt-tolerant archaea have long been known to reside in the Dead Sea, but the details of their day-to-day dealings aren’t fully understood—especially in the lake’s turbulent past. To search for clues of ancient life in the Dead Sea, a team of scientists led by Camille Thomas, a geomicrobiologist at the University of Geneva, drilled more than 1,000 feet into the sediments below.
Entombed in these deep layers are the remains of some of “most extreme periods of Dead Sea history,” Thomas says. At several points in the past, lake levels likely plunged below even where they are today due to the arid climate, boosting the water’s salinity and likely pushing even its most adaptable tenants to the brink.
So the researchers were thrilled when they hit pay dirt at one of these low points, enshrined at 800 feet below the current lake bed (120,000 years ago). Here, there was clear evidence of life—in the form of wax esters, a type of fatty energy-storage molecule that some cells manufacture when food gets scarce.
There was just one problem: Archaea, the Dead Sea’s dominant denizens, don’t make wax esters. But the fatty molecules the team identified still carried traces of archaeal chemicals, as if bits of these cells had been repurposed by another life form.
Thomas and his colleagues found themselves in the middle of a geological whodunnit. Only certain kinds of bacteria and eukaryotes have the ability to synthesize wax esters—but Dead Sea eukaryotes are very rare. This left one probable, and perhaps surprising, culprit: bacteria lurking in the ancient lake’s salty sediment.
Unlike their distant archaeal cousins, which are wrapped in an impermeable sleeve of body armor, bacteria are pretty porous. This sensitivity to their surroundings has made bacteria less common in the Dead Sea, especially on its hostile, dimly lit floor. But by slurping up bits of dead archaea (and likely other cell types as well) and storing them as fuel, ancient bacteria might have found a way to hack it in the lake’s briny, resource-poor brew.
This might actually be a pretty sensible way to ride out the storm, says Jennifer Macalady, a geomicrobiologist at Pennsylvania State University who was not involved in the study. “If you put it on the menu, you would expect some of our microbial biosphere to come and get it.”
What’s more, recycling these remains might have come with a bonus benefit. The same chemical reaction that transforms fragments of deceased archaea into wax esters produces water as a byproduct—something that likely came in handy in a body of water that’s 34 percent salt. This probably would have made for an efficient way to keep from shriveling up, Thomas says.
“These findings are fascinating,” says Cassandra Marnocha, an environmental microbiologist at Niagara University who was not involved in the study. “We’re finding more and more that where it’s physically plausible to find life, life finds a way.”
The work is still preliminary. Though it’s definitely possible that this evolutionary fork in the road yielded a set of salt-tolerant scavengers, more research is needed to solidify the theory, Macalady says.
Part of the challenge going forward, Thomas says, is that there’s not yet evidence this scavenging behavior is still happening today. At the time, this bacterial adaptation probably arose as a last resort, when cells were out of other options, he says. When more favorable conditions came along, scavengers might have been among those that were outcompeted by better-equipped species. And because the researchers weren’t able to recover any DNA in the sediment, it remains unclear what kinds of archaea and bacteria were engaging in this recycling rendezvous.
But as the Dead Sea continues to retreat due to human activity and the changing climate, microbes might once again be forced to take drastic measures. “Today, the Dead Sea is still not at its lowest level or highest salinity,” says Ina Neugebauer, a geologist and climatologist at the GFZ German Research Centre for Geosciences who was not involved in the study. “If the lake level goes further down...then I think this is a strategy that will also happen in the future.”
Beyond the Dead Sea, though, research like this could have implications that are quite literally out of this world. As the search for extraterrestrial life continues, studying Earth’s strangest species could continue to redefine the boundaries of existence—and the extremes to which some will go to survive.
“It’s amazing what these microbes can do, and the types of environments they can live in,” Thomas says. “They can grow over thousands of years, and eat whatever they find. It’s really another way of thinking about life.”
To learn more about the Dead Sea and the ongoing effort to revive and desalinate its waters, watch "Saving the Dead Sea," premiering at 9 p.m. EDT/8 p.m. CDT on Wednesday, April 24 on PBS.