These Sea Sponges Use Toxic Metal As A Creative Survival Strategy
A species of sea sponge found in the Red Sea and Indian Ocean has evolved to have a creative survival strategy.
The sea sponge is called Theonella conica, and like all other sponges, it filters the seawater around them to absorb the nutrients.
Researchers from Tel Aviv University in Israel have found that the seemingly ordinary sea sponge contains high amounts of a toxic heavy metal called molybdenum.
In other organisms, such levels of the mineral would be fatal. This discovery suggests that T. conica uses the metal as a defense mechanism to ward off predators.
“Twenty to thirty 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,” said Shani Shoham, a marine biologist from Tel Aviv University.
Molybdenum is a trace element that is necessary for both humans and animals to metabolize drugs, toxins, and sulfites. Of course, too much molybdenum is not good for us and can be lethal to other organisms.
Shoham wanted to look into whether the sponge species in the deep waters of the Gulf of Eilat had such high concentrations of molybdenum. In the Gulf of Eilat, it grows at depths of over 88 feet.
“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 said.
But how can T. conica accumulate so much of the metal and still survive? The answer lies within the sponge’s bacterial symbionts.
olyphotostories – stock.adobe.com – illustrative purposes only – pictured above boats float on the Indian Ocean, home to these sea sponges
Since T. conica has no tissues, organs, or nervous system, it depends on symbiotic relationships with bacteria, fungi, algae, and viruses to function.
Up to 40 percent of its body weight consists of symbionts living within it. Symbionts are organisms that live together in a larger organism called a host, and both parties benefit from the living situation.
The most prevalent bacteria in the sponge was Entotheonella sp., which acts as a “detoxifying organ” for the accumulation of heavy metals in the sponge’s body.
Shoham and colleagues detected material in Entotheonella sp. that had extremely high molybdenum content.
When the concentration of molybdenum is higher than its solubility in water, the metal becomes toxic.
The researchers believe that the bacteria collects molybdenum and converts it into minerals like calcium molybdate and sodium molybdate. It is unclear why the bacteria does 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.”
The findings have the potential to lead to future research on Entotheonella sp. The bacteria’s ability to hoard toxic metals and turn them into safe minerals can help deal with pollution.
“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,” said Shoham.
The study was published in Science Advances.
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