Far from the sun’s energy, the perpetually ice-covered depths of the Arctic Ocean receive tiny amounts of life-sustaining organic matter. Thus bacteria that can harvest energy from marine hydrothermal sources could have an advantage. On research expeditions with the research vessel Polarstern, scientists from Germany have found that bacteria are uniquely adapted to this geological energy floating in deep sea waters. They describe the role of these bacteria in biogeochemical cycling in the ocean.
Deep in the ocean at tectonic plate boundaries, hot fluids rise from so-called hydrothermal vents. The fluids are oxygen-free and contain large amounts of minerals such as iron, manganese, or copper. Some may also transport sulfides, methane, and hydrogen. When the hot water mixes with the cool, oxidized surrounding seawater, so-called hydrothermal plumes develop that contain smoke-like particles of the mineral sulfide. These columns rise hundreds of meters from the sea floor and disperse thousands of kilometers from their source. Hydrothermals may seem like a risky place to make yourself at home. However, that doesn’t just stop some bacteria from thriving there, according to a study now published in the journal Nature Microbiology Find.
More than just temporary visitors?
“We took a detailed look at the bacteria of the genus sulfurimonassays first author Massimiliano Mollari of the Max Planck Institute for Marine Microbiology in Bremen, Germany. This bacterium has so far been known to only grow in low-oxygen environments, but gene sequences have also been occasionally detected in hydrothermal plumes. He suggests, they have been known to harness energy from sulfides. “And it would have been rinsed there from the environments associated with seafloor vents. But we wondered if the plumes might actually be a suitable environment for some of the members of sulfurimonas group.”
difficult sampling conditions
Together with colleagues from the Alfred Wegener Institute and the Helmholtz Center for Polar and Marine Research in Bremerhaven (AWI) and the Marum Center for Marine Ecology at the University of Bremen, Molari undertook a challenging sampling journey to hydrothermal plumes in the central and southern Arctic. Atlantic Ocean. “We sampled plumes at very remote regions of the ultrasonic propagation edges that had not been studied before. Collecting hydrothermal plume samples is very complex, as they are not easy to locate. Sampling becomes more difficult when the plume is located on depths greater than 2,500 meters and under Arctic sea ice, or within stormy regions of the Southern Ocean,” explains Antje Boetius, group leader at the Max Planck Institute for Marine Microbiology and director of AWI, who was chief scientist on the Arctic missions. On board the research vessel Polarstern, scientists were able to collect samples and within these waters they studied the composition and metabolism of bacteria.
Well equipped and widespread
Mulari and his colleagues identified a new vehicle sulfurimonas species called YuSulfurimonas pluma (superscript “U” stands for uncultivated) It inhabits cold hydrothermal plumes saturated with oxygen. Surprisingly, this microorganism used hydrogen from the plume as an energy source, instead of sulfide. The scientists also investigated the genome of microbes and found that it was shrinking severely, missing genes typical of their relatives, but well-equipped with others to allow them to thrive in this dynamic environment.
“We believe that the hydrothermal plume not only disperses microorganisms from hydrothermal vents, but may also ecologically connect the open ocean with seafloor habitats. Our phylogenetic analysis indicates that YuSulfurimonas pluma It could have derived from an ancestor associated with hydrothermal vents, which acquired a higher oxygen tolerance and then spread across the oceans. However, this still needs further investigation,” says Mulari.
A look at genome data from other poles revealed this YuSulfurimonas pluma It grows in these environments all over the world. “It’s clear that they have found an ecological niche in the oxygen-rich, hydrogen-rich, cold hydrothermal plumes,” says Molari. “This means that we have to rethink our ideas about the environmental role of sulfurimonas in the depths of the ocean – they may be much more important than we previously thought.”
