Study: Gulf Of Eilat Sponges Deter Predators With Toxic Metal

A species of immobile invertebrate organisms called sponges living in the Gulf of Eilat have devised a unique way to ward off predators – an extremely toxic metal called molybdenum.  

Researchers at Tel Aviv University (TAU) found that the Theonella conica sponges contain an unprecedented concentration of the metal as well as a bacterium called Entotheonella that lets them store it safely. 

According to the researchers, sponges are the earliest multicellular organisms known to science. They live in marine environments, where they filter 50,000 times their body weight in seawater every single day. 

PhD student Shani Shoham, who led the study along with Prof. Micha Ilan from TAU’s School of Zoology, said that several decades ago, researchers from the lab found a high concentration of molybdenum in samples of a sponge collected in a coral reef in the Indian Ocean. 

She decided to test whether such high concentrations were also found in the same sponge species in the Gulf of Eilat, where it grows at depths of more than 27 meters. 

Having located the sponge and analyzed its composition, Shoham discovered that it contained 46,793 micrograms of molybdenum per gram of dry weight,  more than any other organism on earth. 

And while molybdenum is in high demand, mostly for alloys such as high-strength steel, Shoham explained that the sponges are an impracticable source of the metal. 

“The concentration is very high, but when translated into weight we could only get a few grams from every sponge, and the sponge itself is relatively rare,” she said. 

Shoham recommended that research should instead focus on how the Entotheonella bacteria allows organisms to accumulate toxic metals, adding that several years ago, TAU researchers discovered massive concentrations of the toxic metals arsenic and barium in the Theonella swinhoei sponge, a close relative of Theonella conica that is common in the Gulf of Eilat.  

“Entotheonella was found to be largely responsible for hoarding the metals and turning them into minerals, thereby neutralizing their toxicity,” she said. 

“Continued research on the bacteria can prove useful for treating water sources polluted with arsenic, a serious hazard which directly affects the health of 200 million people worldwide.”

The findings of the study recently appeared in the Science Advances journal, published by the American Association for the Advancement of Science.

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