How Comb Jellies Thrive in the Ocean's Darkest Depths

Summary

Sources

phys.orgtoday.ucsd.eduphys.org

The ocean's depths present an environment devoid of light, where temperatures plummet to freezing levels, and the pressure from the water above is crushingly intense. Creatures inhabiting these depths have evolved biophysical adaptations to thrive under such conditions. A prime example of such adaptation is found in ctenophores, commonly known as comb jellies. These creatures, belonging to the phylum Ctenophora, are distinct from jellyfish, despite a superficial resemblance. Predatory in nature, comb jellies can grow to the size of a volleyball and reside in oceans globally, from shallow surfaces to the abyssal zones of the deep sea. Cell membranes, composed of thin layers of lipids and proteins, must retain certain properties for cells to function effectively. Traditionally, it was understood that organisms adapt their lipids to maintain fluidity in extreme cold through a process known as homeoviscous adaptation. However, the mystery of how deep-sea organisms adapt to the extreme pressure had remained unsolved. This inquiry led Assistant Professor of Chemistry and Biochemistry Itay Budin from the University of California San Diego, along with a team of researchers, to explore the cell membranes of ctenophores. Their research uncovered that comb jellies possess unique lipid structures enabling them to endure the intense pressures of the deep sea. The study specifically focused on understanding whether adaptations to cold and pressure in ctenophores occurred through the same mechanisms. By examining ctenophores from different environments, including the deep-sea floors of California and the surface waters of the Arctic Ocean, the research team was able to isolate the effects of pressure from those of cold temperatures. The findings revealed that ctenophores have developed distinct lipid structures to counteract intense pressure, a mechanism independent of their adaptations to cold. This adaptation, termed "homeocurvature," involves the evolution of cone-shaped lipids into exaggerated forms that normalize only under extreme pressure. This phenomenon is critical for the integrity of their cell membranes, as the normal appearance of these lipids is maintained only in the deep sea's crushing pressures. Among the lipid structures discovered, plasmalogens—a type of phospholipid—were found in high concentrations in deep-sea ctenophores. Plasmalogens are of particular interest to scientists and medical researchers due to their abundance in the human brain and their association with brain function and neurodegenerative diseases like Alzheimer's. The presence of plasmalogens in such large quantities in ctenophores suggests a potential avenue for further research into their role in human health and disease. The study's findings were bolstered by experiments with E. coli bacteria, some bioengineered to synthesize plasmalogens. These experiments, conducted under high-pressure conditions, demonstrated that E. coli containing plasmalogens thrived, whereas unaltered strains perished. This discovery not only highlights the unique biophysical properties of plasmalogens but also opens up questions regarding their significance in cell function, both in ctenophores and humans. The collaborative effort, spanning several years and involving multiple institutions, underscores the interdisciplinary nature of this groundbreaking research. From biophysics and microbiology experiments at UC San Diego to lipid analysis and marine biology at the Monterey Bay Aquarium Research Institute, and computer simulations at the University of Delaware, this study exemplifies the comprehensive approach required to unravel the complexities of life in the deep sea. Through these efforts, the research not only advances understanding of ctenophores but also prompts further investigation into the biological significance of plasmalogens, potentially shedding light on mechanisms relevant to human brain health and disease. The exploration into the deep-sea adaptations of comb jellies extends beyond the mere ability to survive in cold temperatures; these creatures must also endure the immense pressure that characterizes their environment. The phenomenon of homeoviscous adaptation, which has been a cornerstone of understanding how organisms maintain cellular membrane fluidity under extreme cold, does not entirely explain how life forms like comb jellies withstand the other element of their habitat: the overwhelming pressure. It is the discovery of a unique adaptation termed "homeocurvature" that has illuminated this aspect of deep-sea biology. This adaptation involves the evolution of the lipid molecules in comb jellies' cell membranes, which have developed shapes specifically designed to mitigate the effects of intense pressure. The significance of homeocurvature lies not only in its role in ensuring the structural integrity of cell membranes but also in its critical contribution to the survival of comb jellies in the deep sea. This adaptation allows these organisms to inhabit areas of the ocean that would otherwise be inhospitable, showcasing the remarkable ability of life to evolve and thrive under seemingly insurmountable conditions. Additionally, the research unveiled a fascinating aspect of comb jellies' biochemistry: the presence of plasmalogens in high concentrations within their cell membranes. Plasmalogens are a specific type of phospholipid known to play a significant role in human health, particularly in brain function. Their abundance in comb jellies not only underscores the biochemical kinship between these deep-sea organisms and humans but also opens up potential avenues for biomedical research. The link between plasmalogens and conditions such as neurodegenerative diseases points to the possibility that studying comb jellies could yield insights relevant to understanding and treating such ailments in humans. The journey to these discoveries was made possible through a multidisciplinary approach, combining efforts from various fields of science. From the initial hypothesis posed by researchers intrigued by the parallels between the lipid adaptations in bacteria and the potential for similar mechanisms in ctenophores, to the collaborative efforts involving biophysicists, chemists, marine biologists, and computer scientists, this endeavor exemplifies the power of scientific collaboration. The methodologies employed, ranging from lipid analysis by mass spectrometry to computer simulations of membrane behaviors under different pressures, highlight the comprehensive and innovative strategies necessary to uncover the secrets of life in the extreme environments of our planet. This segment of the research not only advances the understanding of comb jellies and their remarkable adaptations but also emphasizes the broader significance of exploring the deep sea. The findings underscore the importance of investigating the most inhospitable environments on Earth, as such studies can reveal fundamental biological principles and potentially unlock new perspectives on human health and disease.