Deep-sea animals live under high pressure and low temperature, but the molecular adaptations to these conditions are not known. Winnikoff et al. have now identified lipid properties that enable different comb jelly (ctenophore) species to adapt to different ocean depths. The authors analyzed tissue from ctenophores collected at different depths from 0 to 4000 m and temperatures at tropical, temperate and Arctic latitudes. Deep-sea ctenophores disintegrated and exhibited loss of lipid membrane structure at atmospheric pressure. Lipids extracted from deep-sea ctenophores formed a lamellar phase under conditions similar to those found deep in the ocean but changed to a nonbilayer phase at lower pressures. The dominant lipid species in high-pressure environments was plasmenyl phosphatidylethanolamine (PPE), making up 73% of phospholipids from deep-sea ctenophores. PPE monolayers have highly negative curvature under atmospheric conditions, curving toward the lipid headgroups, which transition toward zero curvature with greater fluidity at higher pressures. Another adaptation specific to high pressure was an increase in the acyl chain length of lipids, while the number of double bonds in acyl chains was found to increase with both increasing pressure and decreasing temperature. Moreover, the presence of PPE in membranes found in warm, shallow-water-dwelling ctenophores was offset by a greater presence of positive-curvature-inducing lipids and lipids with more saturated acyl chains. In parallel experiments in Escherichia coli, growth rate and survival were less sensitive to pressure for cells synthesizing PPE compared to control cells. By contrast, E. coli synthesizing the lipid phosphatidylcholine, which increases membrane fluidity but has a low curvature, were more sensitive. Thus, an increase in membrane fluidity is not sufficient for pressure adaptation, unlike cold-temperature adaptation; lipids that induce high membrane curvature are required.
Original reference: Science 384, 1482–1488 (2024)
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