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Theonella conica and Entotheonella symbiosis produces high levels of poison to repel predators

NEWS - Researchers have discovered that the sponge Theonella conica contains highly toxic concentrations of the mineral molybdenum (Mo) and identified the bacteria Entotheonella sp that allow it to store the metal in high concentrations. A sponge symbiosis with bacteria that uses toxic molybdenum to repel predators.

Theonella conica and Entotheonella symbiosis produces high levels of poison to repel predators

The earliest multicellular organisms on Earth lived in marine environments and played a vital role in Earth's carbon, nitrogen and silicon cycles by forming a symbiosis with bacteria. Sponges can process and filter 50,000 times their body weight in seawater every day. They collect various elements including toxic materials such as arsenic and molybdenum.

"We collected samples of the rare sponge Theonella conica from the coral reefs of Zanzibar in the Indian Ocean and found high concentrations of molybdenum in them. Molybdenum is an essential element for metabolism in the cells of all animals including humans, and is widely used in industry," said Shani Shoham of Tel Aviv University.

"Such high concentrations were also found in this sponge species in the Gulf of Eilat at depths of more than 27 meters. The sponge contains more molybdenum than any other organism on Earth: 46,793 micrograms per gram of dry weight," Shoham said.

Molybdenum is toxic when its concentration is higher than its solubility in water, but sponges are essentially hollow masses of cells with no organs or tissues. T. conica contains microbes, bacteria and viruses up to 40% of its own body volume and lives in symbiosis.

One of the most dominant bacteria, Entotheonella sp., functions as a 'detoxification organ' to accumulate the metal in the sponge's body. As molybdenum accumulates, the bacteria convert it from its toxic dissolved state to the mineral state.

"Perhaps the molybdenum protects the sponge by saying: 'I am poisonous! Don't eat me!', and in return the sponge does not eat the bacteria and acts as a host," Shoham said.

Molybdenum is in high demand, for example for making high-strength steel, but it is impractical to recover it from sponges. Converting it to weight, you can only get a few grams from each sponge and the sponges themselves are very fragile creatures that require special conditions. Sponges are farmed in marine agriculture mostly for the pharmaceutical industry.

"Our lab previously found high concentrations of arsenic (As) and barium (Ba) in Theonella swinhoei, which is common in the Gulf of Eilat. Entotheonella is responsible for accumulating the metals and converting them into minerals that neutralize the toxicity. Further research is to use this bacteria to treat arsenic-contaminated water," Shoham said.

Original research

Shani Shoham et al., Out of the blue: Hyperaccumulation of molybdenum in the Indo-Pacific sponge Theonella conica. Science Advances. DOI:10.1126/sciadv.adn3923

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