Biologists have studied the connection of a deep-sea snail in the iron armor with bacteria

(ORDO NEWS) — The gastropod Chrysomallon squamiferum, found on the bottom of the Indian Ocean near black smokers, is sometimes referred to as the “iron snail”. And deservedly so: its shell is indeed composed of iron sulfide.

The armored mollusk “feeds” on hydrogen sulfide, but for this it needs special bacteria. In the new work, scientists learned how this symbiosis works and where the “iron snail” takes such microorganisms from.

Black smokers (more precisely, hydrothermal vents of mid-ocean ridges) are tube-like outlets of very hot and mineral-rich water that, under enormous pressure, break through the ocean floor.

Usually they are confined to rift zones – the place of contact of the oceanic plates of the earth’s crust. These semblances of “geysers at the bottom of the ocean” have become home to unusual creatures that live in complete darkness and do not depend on the energy of the sun.

Among the peculiar inhabitants of black smokers in the Indian Ocean is Chrysomallon squamiferum , also known as the “iron” or ” volcanic snail”.

Rather large compared to its closest relatives (up to 4.5 centimeters), the gastropod mollusk looks armored: it has a thick, often black convoluted shell, and its leg (protruding part of the body) is covered with solid outgrowths-sclerites.

Both the “sheet armor” of the shell and the “chain mail” sclerites contain the mineral pyrite, that is, iron sulfide – there is no other animal on Earth that would use this metal in its skeleton.

Like many inhabitants of black smokers (say, the pogonophora annelids ), the “armored cochlea” subsists on endosymbiotic bacteria living inside its body. Chrysomallon contains cohabitants in a special gland located in the esophagus.

These microbes are able to carry out chemical reactions that allow them to extract energy from hydrogen sulfide – this gas is saturated in water near smokers. Scientists realized this as soon as they pulled the first animals to the surface – by the intense smell.

Until recently, this symbiosis, that is, the mutually beneficial cohabitation of bacteria and mollusks, has been little studied. An article published in the scientific journal The ISME Journal made it possible to learn more about him.

Scientists were interested in how Chrysomallon squamiferum acquires its special bacteria and how genetically close are different snails and their helper bacteria within the same population and from different parts of the Indian Ocean.

Biologists have studied the connection of a deep sea snail in the iron armor with bacteria 2
“Masti” Chrysomallon squamiferum , representatives of populations from different hydrotherms

To do this, we had to work hard: to extract animals from different parts of the seabed, hundreds and thousands of kilometers apart from each other, moreover, from a depth of two and a half kilometers or more.

The mollusks were immediately frozen to a temperature of minus 80 degrees, fixed with special solutions and raised to the surface, where they were dissected and genetically analyzed.

Such animal populations are highly isolated from each other and rarely exchange genes. But, oddly enough, mollusks within the same habitat still differ markedly from each other. This cannot be said about their endosymbiont bacteria, which are genetically quite close.

However, the main question for biologists was how Chrysomallon squamiferum acquires symbionts. Their source can be parents passing bacteria on to their offspring through eggs (this gastropod, like many others, is a hermaphrodite), or the environment, that is, the waters of black smokers.

Biologists have studied the connection of a deep sea snail in the iron armor with bacteria 1
Conditions in two black smokers and how the mollusk obtains its symbionts

Biologists concluded that Chrysomallon squamiferum combines both ways to “infect” the microbes it needs. This makes it possible to obtain bacteria that, on the one hand, are well adapted to the conditions of a given hydrothermal environment, and, on the other hand, are suitable for the mollusk and provide it with everything necessary.

Microbes, in turn, receive a stable and safe, moreover, an armored home, where they can safely catalyze the necessary chemical processes.

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