Unexpected Life Found in the Not-So-Dead Sea

Researchers found green and white mats of bacteria on the bottom of the Dead Sea during a scuba diving expedition that may reveal new insights into the nature of life in extreme environments.

The sprawling communities of bacteria were found near a series of submarine freshwater springs that had never been directly observed by scientists before the summer 2010 expedition. Freshwater from a nearby aquifer must travel through several hundred feet of salty soil before emerging in the sea, creating an unusual chemical mix at the bottom of what is one of the saltiest bodies of water on the planet.

That life exists there at all is still a mystery to the joint Israeli-German research team. Principal investigator Danny Ionescu of the Microsensor Group at the Max Planck Institute for Marine Microbiology in Bremen, Germany, says the presence of biofilms found at the springs is an exciting new discovery.

Ionescu can’t yet reveal specific details on the identity of the bacteria, since the paper documenting the team’s results hasn’t yet been published. “In general,” says Ionescu, “the green biofilms are associated with phototrophs. The white biofilms are normally associated with sulfur-oxidizing bacteria. Never before have these been found in the Dead Sea.”

Phototrophs get their energy from light by photosynthesis, just like flowers and trees. Sulfur-oxidizing bacteria, on the other hand, manufacture their energy through chemical processes when the right ingredients are mixed together. Understanding how life can survive without photosynthesis poses an intriguing challenge for researchers.

Julie Huber, a microbial oceanographer at the Marine Biological Laboratory of the Woods Hole Oceanographic Institute, explains: “What those types of organisms are really looking for is a place where they have a source of hydrogen sulfide up against a gradient of oxygen, or methane-oxygen….And [the bacteria] are basically exploiting that gradient.”

Huber is an expert on the oddities of life near underwater volcanoes, where warm fluids leak out of the Earth’s crust and create wildly diverse ecosystems, referred to as hydrothermal vents. Similar types of bacteria have been found there, she says, and in other diverse environments all over the world, including caves, sulfur springs, and even within strange ocean currents. “Any place where you see these extreme gradients in chemistry is where you often find [sulfur-oxidizing bacteria].”

Finding these bacteria at the Dead Sea comes as a surprise to researchers, who have known for decades that the “dead” in the Dead Sea may be a misnomer, but it isn’t far from the truth.

“It is interesting as an extreme environment,” says Ionescu of the Dead Sea. “Unlike other hypersaline lakes or ponds it has a very low [bacteria] cell abundance, at between 1,000-10,000 per milliliter.” This is far lower than typical ocean ecosystems.

Because the Dead Sea contains a salt concentration of nearly 35 percent (roughly ten times saltier than the ocean), large life forms like fish and plants can’t survive there, though bacteria have been found in Dead Sea water as early as the 1930s.

Ionescu got a rare opportunity to experience the salty sea up close by serving as one of the scuba divers on the expedition. He says the team required special equipment, training, and permission to obtain their samples.

“First of all we used a full face mask—this is the most important factor, as swallowing Dead Sea water can be lethal and getting it in your eyes is also not fun,” says Ionescu. Since the high salt content makes the water unusually buoyant, he needed to wear 80 pounds of lead weights to reach the 100-foot deep springs. That’s twenty times the weight he’d normally use while diving in the ocean.

Though dangerous to reach, the Dead Sea’s freshwater springs offer an exciting training ground to better understand what makes life tick.

“Why can [the freshwater] travel over hundreds of meters without getting really saline?” wonders Christian Siebert of the Department of Catchment Hydrology at the Helmholtz Center for Environmental Research in Germany. “That’s fascinating. And in the end, we can see organisms, surviving in a toxic environment all because of this freshwater supply.”