At the Aurora Vent Field, Enceladus black smoker. Credit: HACON cruise 2021, REV Ocean
Hydrothermal vents near tectonic plate boundaries release hot fluids that are without oxygen and are abundant in metals such as iron, manganese, and copper, as well as potentially storing sulfides, methane, and hydrogen. As the hot water interacts with the cold, oxygen-rich seawater nearby, it forms hydrothermal plumes composed of smoke-like metal sulfide particles.
Hydrothermal plumes may appear to be inhospitable environments, rising hundreds of meters from the seafloor and dispersing thousands of kilometers from their origin. Yet, a recent research discovered that specific bacteria flourish in these seemingly precarious environments.
Polarstern, a research vessel, was stationed in the Greenland ice at a depth of 4000 meters above the Western Vulcanic Zone of Gakkel Ridge on the Alfred Wegener Institute's PS86 expedition.
"We examined bacteria of the genus Sulfurimonas", according to the first author at the Max Planck Institute for Marine Microbiology in Bremen, Germany. These organisms have till now only been discovered in low-oxygen environments, although gene sequences had occasionally also been detected in hydrothermal plumes, according to their name.
"We assumed that the plumes came from seafloor vent-associated environments. But we wondered if the plumes might actually be a suitable environment for some members of the Sulfurimonas group."
Gunter Wegener, Massimiliano Molari, Mirja Meiners, Antje Boetius, Fabian Schramm, and Norbert Rieper are among those who contributed to the Polarstern team, led by Prof. Dr. Antje Boetius. Back row, from left: Andreas Türke, Yann Marcon. Credit: Alfred Wegener Institute
Molari traveled to the Central Arctic and South Atlantic Ocean with colleagues from the Alfred Wegener Institute, the Helmholtz Centre for Polar and Marine Research (AWI) and the Bremen University's MARUM Center for Marine Environmental Sciences.
“We sampled hydrothermal plumes in remote locations that had never been studied before,” says Antje Boetius, group leader at the Max Planck Institute for Marine Microbiology and director of the AWI.
Hydrothermal vents at Gakkel Ridge (Central Arctic) using the underwater camera system OFOS, which allowed us to spot the location of the hydrothermal vents field during expedition PS86.
The scientists collected samples and studied bacteria's composition and metabolism aboard the Polarstern research vessel.
USulfurimonas pluma (the superscript "U" stands for uncultivated) was discovered in the cold, oxygen-saturated hydrothermal plumes by Molari and his colleagues. The microbes' genome was found to be severely reduced, lacking genes typical for their relatives, but being equipped with others to thrive in this fast-paced environment.
"Our phylogenetic research suggests that USulfurimonas pluma may have derived from a hydrothermal vent-associated ancestor, who acquired greater oxygen tolerance and spread across the oceans," says Molari.
USulfurimonas pluma has grown in these environments throughout the world, according to Molari. "They have discovered an ecological niche in cold, oxygen-saturated, and hydrogen-rich hydrothermal plumes," which means we need to reconsider our assumptions about the ecological role of Sulfurimonas in the deep ocean.
Massimiliano Molari, Christiane Hassenrueck, Gunter Wegener, Pierre Offre, Stefano Scilipoti, and Antje Boetius, 9 March 2023, Nature Microbiology. DOI: 10.1038/s41564-023-01342-w
