Strange triple alliance discovered between a sea slug, algae and bacteria

A very interesting three-way symbiotic relationship between a species of sea snail, a seaweed species and a bacterium species was discovered by a Princeton University research group. Researchers have discovered that Elysia rufescens, a species of sea snail from the Plakobranchidae family, is used to eat seaweeds of the genus Bryopsis to build its own chemical “arsenal” to defend itself from predators.

This sea snail is known because it uses chemical compounds to defend itself from predators and these compounds build them by taking the toxic chemicals present in the algae that are in turn produced by a new species of bacterium, discovered by Princeton scientists, which they live within the latter. The bacteria themselves are literally dependent on their “home” and cannot survive except in that particular alga. Precisely for this reason, one-fifth of their metabolic efforts are dedicated to the production of these particular poisonous molecules.

These bacteria, which the scientists then called Candidatus Endobryopsis kahalalidefaciens, are able to produce about 15 different toxins, in turn called kahalalides. These substances serve as alga as a deterrent to not be eaten en masse by fish and other marine animals.

These bacteria are no longer able to live outside the algae because, as the researchers themselves have verified, they no longer have the genes needed to live outside. They spend almost all their lives pumping these toxic molecules that are needed by the alga to protect themselves. However, there is a predator, the sea snail Elysia rufescens, which is capable of resisting these toxins. It stores them and thanks to them it builds another chemical arsenal, even more powerful than that of algae, to counteract its predators.

It does not acquire the ingested bacteria, which are digested as food, but only the substances that these bacteria produce inside the algae. This is a triple complex symbiotic system that Mohamed Donia discovered when he tried to understand how algae defend themselves from other marine organisms, even with the hope of discovering chemicals for creating drugs.