How 'ctenophores' survive and thrive under deep ocean pressure

Any discussion about the ocean’s mysteries is incomplete without the “comb jellies” or ctenophores, the vivacious deep-sea dwellers.

With a survival finesse that rivals the most experienced deep-sea divers, ctenophores are shedding new light on adaptation and survival at extreme pressures.

Their secret? There’s something “fatty” about their technique.

Lipids, ctenophores, and the deep blue sea

One would ask, how does a simple deep-sea creature defy so much pressure? A team of researchers that includes University of Delaware biophysicist Edward Lyman and doctoral students Sasiri Vargas-Urbano and Miguel Pedraza Joya have got us an answer.

The study co-authored by these scientists, first-author Jacob Winnikoff, now at Harvard University, Steven Haddock, an MBARI marine biologist, and project principal investigator Itay Budin, an assistant professor at UC San Diego, has some news that’s, literally, deep.

The secret lies in the lipids. These fatty chemical compounds found in all living cells perform essential functions like storing energy, sending signals, and controlling what passes through the cell membrane. It seems, for the comb jellies, lipids also serve as their pass for survival in the ocean.

These findings about marine organisms’ adaptation might inform us about lipids found in our nerve cells, particularly how it might work in our brains.

Who would think studying jellies could help us understand ourselves better?

What are ctenophores?

They might look like jellyfish, but ctenophores, or “comb jellies,” are actually a different kind of marine animal called Ctenophora. What makes them special are the rows of tiny plates, or “combs,” they use to swim.

These combs catch the light and create beautiful rainbows as they move through the water, which is a sight that amazes both scientists and ocean lovers.

Most of the time, comb jellies are see-through or slightly see-through. Instead of stinging, they have tentacles with sticky cells called colloblasts to catch their food.

These amazing creatures play important roles in the ocean by helping to control the number of zooplankton. Their unique way of living and surviving in tough ocean conditions keeps scientists curious and eager to learn more about them.

They are predators found at various depths in the ocean, doing a lot of eating and serving as a food source themselves.

According to UD’s Lyman, these ctenophores are the first things that branch off from the rest of the animals.

“This means that you and I are more closely related to a jellyfish than a jellyfish is to a ctenophore,” says Lyman. Doesn’t it feel good to have a jellyfish as a distant cousin?

Deep-sea adaptation

What’s more fascinating is that Lyman and his team found an adaptation in the cellular membrane of deep-sea dwelling ctenophores that enables them to survive under extreme pressure.

Their findings revealed that deep-sea ctenophores have a huge abundance of the lipid molecule, plasmalogen.

“What makes plasmalogen lipids interesting is that they allow cell membranes to bend and deform, even in the deep ocean at high pressure, where membranes would otherwise be very stiff, and that’s a useful adaptation,” explains Lyman.

By running experiments and simulations, Lyman and his team discovered that it’s the chemistry of a lipid molecule that determines whether it wants to reside in a membrane that’s flat or curved. Processing data for simulations about 500 nanoseconds long even took about a month to create.

In the end, it was clear. The structure of ctenophore membranes changes under various pressures, indicating that ctenophore lipidomes are specialized for high pressure.

E. coli, ctenophores, and pressure

Due to the weight of the water that lies above, the deep sea is under extreme pressures equal to that of hundreds of atmospheres.

The team’s investigation into ctenophore secrets centered around E. coli, a common resident of the human gut, and its response to the extreme pressures endured by the deepest dwelling ctenophore.

Such pressures, the scientists noted, could be around 500 times that at the ocean’s surface, a significant limiting factor for the E. coli‘s growth. However, when these cells were enabled to synthesize plasmalogen lipids, they were able to proliferate as normal.

An interesting twist came to light when this cell membrane was simulated in a digital environment and stress-tested under varying temperatures and pressures.

The team at UD revealed that it was indeed the plasmalogen lipids that kept these membranes flexible and adaptable under high pressure.

“Using molecular-dynamic simulations to explore this system, we were able to test conditions that would be found even deeper in the sea than these ctenophore species actually live to see what happened,” explained team member Vargas-Urbano.

Role of plasmogens

The deep-sea ctenophores’ cell membranes carried more plasmalogen lipids compared to other species found near the surface or in the Arctic.

One type of plasmalogen, termed PPE, was particularly abundant in the deep-sea creatures and exhibited a distinct conical shape.

As per simulations by UD researchers and artificial membrane experiments by Budin and Winnikoff, increased presence of PPE resulted in the membranes curling up, even under lower pressures.

In what turned out to be a notable revelation, a significant correlation was found between the amount of plasmalogen in a ctenophore species’ cellular membrane and where it could survive.

However, when the membrane of surface-dwelling ctenophores was compared with their deep-sea counterparts in their natural habitats, they exhibited similar characteristics in terms of molecular adjustment within the cell to stabilize the membrane.

The scientists termed this as “homeocurvature adaptation,” a mechanism where the ctenophores and their lipidomes have adapted to their residing conditions.

This could potentially explain why deep-sea invertebrates, including ctenophores, disintegrate when brought to the surface.

Ctenophores, lipids, and human health

The discovery of how life adapts to extreme conditions in the ocean could provide valuable insights into the human body. As Lyman elaborated, plasmalogen lipids found in ctenophores are also present in human bodies, predominantly in neural tissue.

“Nerve cells in the brain transmit messages by sending chemicals from one cell to another. And there is an awful lot of plasmalogen at the site where all that synaptic transmission is happening in your neurons,” he explained.

The depletion of plasmalogen has been associated with conditions such as Alzheimer’s disease, which signifies that a deeper understanding of plasmalogens may have potential benefits for other areas of research.

In summary, this study provides intriguing insights into the survival mechanisms of deep-sea creatures. It uncovers the remarkable role of plasmalogens and how their presence affects the adaptability of ctenophores to their environment.

Moreover, the implications of this research stretch beyond marine biology, potentially influencing our understanding of human health, specifically neurology, shedding light on plasmalogens crucial role in the human brain.

The full study was published in the journal Science.

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