'Talented' Mutant Bacteria Could Save the Thirsty World From Arsenic

Sponges were discovered with a million times the normal arsenic concentration, yet they didn't make sea slugs sick, a discovery that could save human lives.

Theonella: This sponge had been thought capable of myriad wonders, some of which turn out to be properties of a symbiotic bacteria, Entotheonella, which mineralizes and sequesters arsenic and barium.
Theonella: This sponge had been thought capable of myriad wonders, some of which turn out to be properties of a symbiotic bacteria, Entotheonella, which mineralizes and sequesters arsenic and barium. Nick Hobgood, Wikimedia Commons

Technologies to filter the naturally occurring poison arsenic from groundwater are legion, and expensive. It turns out that a primitive form of life, the Theonella sponge, gets that service for free from a 'talented' mutant bacteria discovered in the Red Sea.

Asia particularly suffers from arsenic, but it also exists in parts of North America. Some foods concentrate the mineral too, most notoriously, rice. Around 150 million Asians routinely drink water laced with arsenic and as populations grow. In time arsenic buildup leads to nervous and cardiac damage and cancers. That's in us.

Arsenic isn't good for sponges, either. But in the Red Sea, they're safe thanks to a bacterium living symbiotically with the sponge, that isolates the arsenic in intracellular vesicles, and renders it inert.

The discovery of the bizarre germ-sponge symbiosis arose from the 2014 discovery that these Theonella sponges have a million times more arsenic than that found in seawater.

Theonella swinhoei sponges everywhere live in symbiosis with a large population of a tough sea-dwelling bacterium called Entotheonella. But a mutant version of the bacteria in the Red Sea, and only there, accumulates and converts vast amounts of arsenic, says Prof. Micha Ilan of Tel Aviv University, who headed the research team of the paper published in Nature Communications. The other variants of the bacteria also soak up arsenic and barium but in far smaller amounts.

Moreover, Entotheonella also mineralizes and neutralizes barium, another notorious element, both inside its cells.

The sponge is happy. Why, evolutionarily speaking, the bacteria would deposit arsenic and barium remains a mystery, Ilan admits to Haaretz: it might have to do with deterring predators.

Pharmacologists have been looking at sponges for decades, seeking (and finding) compounds with bio-activity (that have some effect on our bodies if we take them). It turned out, Ilan says, that no small part of the dozens of compounds they isolated from the sponge Theonella swinhoei, had been the responsibility of Entotheonella bacteria, not the sponge at all, he explains - and that is why they're called "talented bacteria".

They're such a talent that if the sea slug eats a sponge absolutely "exploding with arsenic," as Ilan puts it, nothing will happen because the Entotheonella rendered the arsenic non-toxic. (Actually, the sea slug, Red Spanish Dancer, even evolved to deal with the myriad of bioactive compounds and skeletal elements made of glass found inside this incredible sponge, Ilan adds).

Perhaps the Entotheonella or its arsenic-fixing mechanisms can be harnessed to treat contaminated groundwater. "To render this unique detox method applicable to other situations, we need to somehow get rid of the sponge," Ilan sums up. "In other words, there is a lot more work to be done before we, human beings, can capitalize on this." As world populations continue to grow and the water supply continues not to grow, and as thirsty communities increasingly tap contaminated groundwater, that would be useful.