How do comb jellies survive crushing pressure in the deep ocean?

The ocean’s depths are an inhospitable environment with no light, freezing temperatures, and crushing pressure. However, certain marine organisms, such as ctenophores (commonly known as comb jellies), have evolved unique adaptations to survive these extreme conditions.

A team of researchers led by Itay Budin, an assistant professor of chemistry and biochemistry at the University of California San Diego, explored these adaptations, focusing on the cell membranes of ctenophores. 

The analyses revealed that these organisms possess unique lipid structures that help them withstand high pressure.

Pressure adaptation in comb jellies 

Unlike jellyfish, comb jellies can grow as large as a volleyball, living in oceans globally at varying depths. Their cell membranes, which consist of thin sheets of lipids and proteins, need to maintain specific properties to function correctly. 

While some organisms have long been known to adapt their lipids to maintain fluidity in extreme cold through homeoviscous adaptation, the adaptation to pressure in deep-sea organisms was not well understood.

“Hydrostatic pressure increases with depth in the ocean, but little is known about the molecular bases of biological pressure tolerance,” wrote the study authors. “We describe a mode of pressure adaptation in comb jellies (ctenophores) that also constrains these animals’ depth range.”

Unique lipid structures 

Budin’s team examined comb jellies from different environments, including those from the bottom of the ocean in California and the surface of the Arctic Ocean, to study whether these organisms adapted to cold and pressure through the same mechanism. 

They found that comb jellies have developed unique lipid structures, known as “homeocurvatures,” which are distinct from those used to adapt to cold. 

The lipids in deep-sea ctenophores evolved into exaggerated cone shapes, counteracted by ocean pressure, maintaining the normal lipid shape only at extreme depths. When these creatures are brought to the surface, their cell membranes split apart, and the animals disintegrate.

Comb jellies and human brains

The researchers discovered that these exaggerated cone-shaped molecules are a type of phospholipid called plasmalogens, which are also abundant in human brains. 

The study revealed that plasmalogens make up as much as three-quarters of a deep-sea ctenophore’s lipid count. Given the significant role of plasmalogens in brain health and their association with neurodegenerative diseases, this finding is particularly intriguing.

Further experiments with E. coli in high-pressure chambers demonstrated that bioengineered bacteria synthesizing plasmalogens thrived under high pressure, while unaltered bacteria did not. 

The role of plasmalogens in brain health

Budin hopes that this discovery will lead to further research on the role of plasmalogens in brain health and disease. 

“I think the research shows that plasmalogens have really unique biophysical properties. So now the question is, how are those properties important for the function of our own cells? I think that’s one takeaway message.”

The study is published in the journal Science.

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