The element arsenic, infamous in history as a poison – perhaps claiming the life of Napoleon Bonaparte – is a modern problem as well. The U.S. government lists arsenic as the most common toxin in the natural environment.

But what is poison to humans may be chow for so-called extremophiles, creatures that thrive in harsh environmental conditions unsuitable for nearly all other forms of life, including hot, acidic springs or oceanic thermal vents. Last year, for example, researchers from the U.S. Geological Survey found bacteria making a hardy living in Yellowstone National Park by using arsenic to conduct photosynthesis, the chemical process that converts sunlight into usable energy. Mind you, in humans arsenic in large quantities can kill in an hour, and smaller doses can lead to illnesses including cancer and foot growths known as keratoses.

Scientists have now discovered algae, called cyanidioschyzon, that survive in the presence of heavy levels of arsenic also found near Yellowstone’s scalding springs. Algae are plant-like organisms that range in size from a single cell up to many-celled clumps of seaweed.

Cyanidioschyzon withstand arsenic in two ways, according to a new study published recently in Proceedings of the National Academy of Sciences. One, they keep the most biologically lethal forms of it from entering their cells and somehow – in ways as yet unknown – change it into a form that’s 10 times less toxic. And two, the creatures turn less poisonous arsenic compounds that do get inside them into a gas that evaporates without causing harm from their single-celled bodies. 

These algae that detoxify arsenic may help with bioremediation efforts, which employ life forms, such as trees, in restoring polluted habitats. Much like the bacteria that may one day be commonly used to gobble oil after a spill, these arsenic-fighting algae may assist in cleaning up contaminated mining areas, says study co-author Tim McDermott, a professor of microbial ecophysiology at Montana State University in Bozeman. For now, the algae merely bring down local toxicity levels, McDermott notes, but even that could prove useful.

An open question, McDermott says, is where the gasified arsenic ends up when it leaves the algae. “We do want to know where the arsenic re-deposits and under what conditions. That’s something researchers will definitely be looking into,” McDermott says. “After all, arsenic is still arsenic.”

Algal mats in the Norris Geyser Basin in Yellowstone National Park. Image Credit: National Park Service