Hydrothermal vents lie in perpetual darkness in the depth of the ocean, yet the cells of the vent mussel Bathymodiolus azoricus, who lives 1,700 metres below the surface, follow a 24-hour rhythm in the laboratory. Researchers from the University of Vienna and the partner institutions IFREMER in France, the University of Oldenburg and the AWI in Germany established cell cultures from these deep-sea mussels, which now allow cellular and molecular insights into the mechanisms of biological timing in the deep sea. The study was published in the journal EMBO Reports. It shows that in the tide-driven environment of the mussels, biological timing can rely on the same genes as the 24-hour clock that regulates land-dwelling organisms.
Living to the rhythm of the tides
At a depth of 1,700 metres, the deep-sea mussel Bathymodiolus azoricus shapes the ecosystem at hydrothermal vents. Its living conditions are extreme by human standards: the mussels colonise the seafloor around the vent chimneys and must withstand high pressure as well as the influence of hot, heavy-metal-rich fluid. This fluid forms when seawater permeates into the seafloor, passes through the underlying rocks and pours back into the ocean as hydrothermal fluid. Its direction of flow shifts with the tides, which is presumably why the mussels at these vents show tidal rhythms in both their behaviour and their molecular biology. How organisms without a brain generate such rhythms has so far remained unclear.
A world first: deep-sea cells in the fridge
For the first time, the team succeeded in establishing cell cultures from mussels, which have now been maintained in the laboratory for over three years. Audrey Mat, first author of the study and initiator of the experiments, explains: "While cells in the laboratory usually thrive at 25 to 37 °C, our mussel cells grow in the fridge, at deep-sea temperatures. This technical advance is unique in the world and allows novel insights into the biology of these animals."
From tides to a daily rhythm
Interestingly, the mussels' rhythm changes from tidal rhythms on the deep seafloor to mainly circadian rhythms in the laboratory. The circadian rhythm can even be observed independently in cell cultures. This suggests significant plasticity in the clock machinery.
Deep-sea mussels possess the core circadian clock genes found in organisms ranging from flies to humans, albeit with specific modifications. These modifications could enable the clock to shift between circatidal (12.4-hour) and circadian (24-hour) timing, presumably through changes in the expression of the clock gene period .
Relevance for protecting the deep sea
The deep sea is one of the least explored ecosystems on Earth and is under considerable pressure from human exploitation, such as pending deep-sea mining. "The fact that these ecosystems are mechanistically highly complex and possess timing systems as sophisticated as those at the surface underlines how worthy of protection they are. On land, we know that human activities such as light or vibrations disrupt circadian clocks. Deep-sea clocks are very likely just as vulnerable, with significant consequences for organisms and ecosystems," say Kristin Tessmar-Raible and Marjolaine Matabos, the joint coordinators of the study.
Summary
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For over 650 years the University of Vienna has stood for education, research and innovation. Today, it is ranked among the top 100 and thus the top four per cent of all universities worldwide and is globally connected. With degree programmes covering 188 disciplines, and approximately 11,000 employees, we are one of the largest academic institutions in Europe. Here, people from a broad spectrum of disciplines come together to carry out research at the highest level and develop solutions for current and future challenges. Its students and graduates develop reflected and sustainable solutions to complex challenges using innovative spirit and curiosity.
EMBO Reports
Endogenous rhythms in deep-sea mussel cell culture and molecular clock characterization
2-Nov-2026