Great Salt Lake Nematodes Discovered in Extreme Salinity

For decades, the Great Salt Lake in the United States was officially believed to contain only two animals larger than a single cell: brine shrimp and brine flies.

Beyond these, the lake's extremely salty water was known to support only bacteria and algae.

Scientists have now uncovered a third type of multicellular organism capable of tolerating an unpalatable level of salt. It had been concealed in the lake all along.

Nematodes beneath Great Salt Lake microbialites

Researchers at the University of Utah broke apart lumps of calcium-carbonate mud known as microbialites, which are formed by microorganisms on the lake bed. In doing so, they verified a long-held biological suspicion: several species of worms are writhing beneath the lake's surface, out of view.

This is the saltiest setting in which nematodes have ever been discovered. That is notable because nematodes inhabit virtually every extreme environment on Earth.

Biologists Julie Jung and Michael Werner headed the worm-discovery team. In spring 2021, they launched a thorough search in an area of the lake with salinity levels three to six times higher than the ocean.

"At first it was just scooping up segment samples. But then once we noticed microbialites, we shoveled little chunks of them, tried to preserve the layers, and brought them back to the lab," explains Jung.

Jung and Werner succeeded where previous biologists had not.

Using a powerful method for separating macromolecules such as DNA, RNA and proteins, the team detected living nematodes at every sampling site.

"I'd looked there myself for them, but I didn't look in the same places… " says biologist Byron Adams from Brigham Young University, who consulted on the discovery.

"Even today we're discovering these amazing things about this lake that's been sitting on our doorstep for 170 years."

How the Great Salt Lake worms may survive

The scientists believe the concealed worms feed on bacteria that inhabit and produce these mats. The mats may also shield them from sunlight and prevent them drying out when the lake water retreats.

Because the researchers were unable to culture the nematodes in the laboratory, they investigated the worms' survival using the best-studied roundworm of all: Caenorhabditis elegans.

In laboratory tests, this species received either E. coli bacteria or bacteria found in Great Salt Lake microbial mats. The worms were subsequently exposed to lake water, which is 50 times saltier than the normal habitat of C. elegans.

Within five minutes, worms fed E. coli had died. Those maintained on microbes from the Great Salt Lake, however, remained alive for more than 24 hours.

"We didn't expect it to work, but it did," says Werner.

These findings indicate that some feature of this specific diet enables roundworms in the Great Salt Lake to endure.

Newly found species face a drying lake

Genetic analysis suggests that researchers collected up to 80 distinct nematodes from brackish and hypersaline areas of the lake. Three belong to a genus found in marine and coastal sediments. Most of the others did not correspond with any known nematode genus or species.

The researchers believe these previously unknown worms are exclusive to the Great Salt Lake, having emerged following an extended period of reproductive isolation. Now that this habitat and its new species have been identified, they may be at risk of vanishing permanently.

The Great Salt Lake is now only a remnant of its former self. Water diversion for human use and an increasingly dry climate are causing its shores to recede, leaving microbial mats exposed to the elements and raising the salinity of the water that remains. As the lake has dried, Werner and Jung have had to abandon their kayaks and travel by mountain bike to reach certain sites in some seasons.

Some scientists believe fewer than five years remain before the ecosystem fails entirely. What that would mean for its worms is unknown.

"There is a pressing need to understand this lynchpin community and the limits of their habitability," conclude Werner, Jung, and their colleagues.

The study appeared in Proceedings of the Royal Society B: Biological Sciences.