California’s Saltiest Lake Is Home to This Arsenic-Resistant, Three-Sexed Worm

Prior to their discovery, only two species could survive in the super-salty, highly alkaline lake in the Sierra Nevada mountains

Arsenic Nematode

It’s no stretch to say Mono Lake, located in the eastern Sierra Nevada Mountains, is one of the weirdest bodies of water in the United States. For example, it’s three times as salty as the ocean. It has an pH of 10, making it as high in alkalinity as milk of magnesia. Rising from its strange waters are tufa towers, or naturally erected columns of limestone. Conditions are so harsh that it’s believed only two species could survive in its waters: a brine shrimp and a diving fly.

But a new study published in the journal Current Biology has now described a third type of extremophile in Mono Lake, a group of microscopic nematode species that are as unusual as the lake they live in.

California Institute of Technology (Caltech) biologist Paul Sternberg and his team typically study the genomes of microscopic worms called nematodes, which are the most abundant multicellular creatures on Earth, reports Abby Olena at The Scientist. However, in their free time, some members of the lab search out nematodes in unusual places. In the summer of 2016, Amir Sapir was a postdoctoral researcher in Sternberg’s lab when he and some colleagues decided to dig up samples from three sites around the lake. Sapir, now a biologist at University of Haifa-Orani, and his team sampled scoops of dirt from the dry lakeside, the intertidal zone and from sediment within the lake.

When they analyzed the samples, they found nematodes living in all three areas, representing eight species in total. According to the paper, three were already known to science, but the other five were unknown. Looking at the shape of their mouthparts, the team predicted that the nematodes had different lifestyles; some were adapted for grazing on microbes, some were designed for predation and others were set up for parasitizing a host animal.

The team found that the Mono Lake nematodes are quite unusual. All of them show resistance to arsenic at 500 times the dose lethal to humans.

“Extremophiles can teach us so much about innovative strategies for dealing with stress," study coauthor Pei-Yin Shih of Caltech says in the press release. “Our study shows we still have much to learn about how these 1000-celled animals have mastered survival in extreme environments.”

One of the new species, however, is particularly exciting. According to a press release, creatures that live in extreme conditions, like tardigrades, are difficult to culture in the lab. But one of the new nematodes from the genus Auanema did reproduce in the lab, which will provide researchers a new model extremophile to work with.

The as-yet-unnamed Auanema species has three sexes, male, female and hermaphrodite, reports Ryan F. Mandelbaum at Gizmodo. It also raises its larvae in a pouch, like a microscopic, wormy kangaroo.

The team found that Auanema resists arsenic due to a mutation in the Auanema dbt-1 gene, reports Olena. When they looked at three other nematode species in the genus Auanema collected from less-harsh conditions, the team found that they too carried the mutation. The finding suggests that those nematodes have a genetic predisposition to adapting to many different environments.

“Mono Lake is famous for being a limited ecosystem in terms of animals . . . so it’s really cool that they’ve managed to demonstrate that there are a bunch of nematode species living in there, as well as the shrimp and the flies,” microbiologist Lucy Stewart of GNS Science in New Zealand, who not involved in the study, tells Olena. “It expands the whole ecosystem considerably.”

Learning about extremophiles and how they deal with environments like the deep ocean, volcanoes, ice caps and arsenic-contaminated lakes can teach scientists how humans could use similar strategies to develop new types of agriculture or show us how to live on other planets.

“Perhaps we can figure out new pathways that animals such as ourselves may be able use to our advantage,” study coauthor James Lee, a molecular biophysicist from Rockefeller University, tells Mandelbaum.

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