Rare sea creature may provide solution to heavy metal pollution

Earth boasts a very hostile environment, where survival is the core drive for any creature.

Such brutal surroundings have stimulated plants and animals to develop uncanny mechanisms for survival. For instance, the Hypenea macrantha plant uses explosives to remove rival pollen from pollinators.

In those efforts, a sea sponge called Theonella conica has developed a fascinating survival strategy by absorbing the highly toxic mineral Molybdenum.

A study conducted by Tel Aviv University found that T. conica has developed this way of survival to keep predators away.

T. conica is a relatively less studied sponge widely distributed in the Red Sea and Indian Ocean. Recent studies have focused on the sponge’s ability to produce bioactive compounds.

While Molybdenum is a transition metal and an essential micronutrient, its high concentration could be fatal. Therefore, most living animals don’t accumulate molybdenum.

However, T. conica has shown exceptionally high concentration levels of molybdenum, which is not common in companion sea sponges like T. swinhoei.

“20 to 30 years ago, researchers from our lab collected samples of a rare sponge called Theonella conica from the coral reef of Zanzibar in the Indian Ocean and found in them a high concentration of molybdenum. Molybdenum is a trace element, important for metabolism in the cells of all animals including humans, and widely used in industry,” says PhD student Shani Shoham.

“In my research, I wanted to test whether such high concentrations are also found in this sponge species in the Gulf of Eilat, where it grows at depths of more than 27 meters. Finding the sponge and analyzing its composition I discovered that it contained more molybdenum than any other organism on earth: 46,793 micrograms per gram of dry weight.” Shoham continued.

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The molybdenum element is considered a pollutant in water and soil and is often found in sedimentary deposits rich in oxides. Therefore, rivers serve as the primary source of molybdenum in open seawater.

While molybdenum is associated with sponges, researchers found no correlation between the proximity of sponges and the measured molybdenum concentration.

To dig out this enigma, the team experimented with the sponge and discovered that the accumulation was the result of a symbiotic relationship. Entotheonella sp. is a dominant bacterium, responsible for molybdenum hyperaccumulation.

“In Theonella conica, up to 40% of the body volume is a microbial society – bacteria, viruses, and fungi living in symbiosis with the sponge. One of the most dominant bacteria, called Entotheonella sp., serves as a ‘detoxifying organ’ for accumulating metals inside the body of its sponge hosts. Hoarding more and more molybdenum, the bacteria convert it from its toxic soluble state into a mineral,” says Shoham.

Even the researchers are unsure about the reason behind hoarding more molybdenum. They hypothesize it is a survival mechanism, which also explains the deep blue color of T. conica.

“We are not sure why they do this. Perhaps the molybdenum protects the sponge, by announcing: “I’m toxic! Don’t eat me!”, and in return for this service the sponge does not eat the bacteria and serves as their host.”

In a statement, Shoham asserted that we can get a few grams of the heavy metal from T. conica, but it’s not worth extracting.

Shoham focuses on the ability of Entotheonella to hoard the metals into minerals and neutralize their toxicity. This ability can be utilized to treat heavy metal pollution.

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

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