Cloudy material drifting from chimneys at the bottom of the ocean may contain microscopic life forms that scientists didn’t even know existed until now.
Ridges on the ocean floor are littered with cracks called hydrothermal vents that spewing hot liquids from the Earth’s interior containing hydrogen sulfide, methane and hydrogen into the ocean. And around the warm surroundings of these dynamic nutrient distributors is a host of hungry, mysterious microbes that use the chemicals released from the vent to thrive in the absence of sunlight or excess oxygen.
But these may not be the only exits of microbes through the holes.
A new study has identified a genus called Sulfurimonas that can not only thrive around hydrothermal vents, but also live in the cool, oxygenated tissues seeping overhead.
These clouds of smoke can extend hundreds of meters up and kilometers out. This happens when hot magma mixes with cold seawater, and is made up of a completely different list of chemicals for the hydrothermal vents it comes from.
Sulfides are known to be the dominant players around hydrothermal vents, easily surviving in warm, oxygen-depleted water, and using sulfides ejected from vents for energy, but these new results show that some species have already evolved to rise up with plumes.
Previous studies have sampled the tops of hydrothermal plumes and found genetic markers of Sulfurimonas, but it was thought that the bacteria did not actually grow in the cloud. The plumes are believed to be very cold and oxygenated.
“(Bacteria) must have gotten there from environments associated with seafloor vents,” explains marine microbiologist Massimiliano Mollari of the Max Planck Institute in Germany. “But we wondered if plumes might actually be the right environment for some members of the Sulfurimonas group.” .
Sampling hydrothermal plumes is a tricky business. This requires expeditions to remote areas of the ocean, where the boundaries of tectonic plates are gradually being eroded.
These regions are not easy to find, and even when found, sampling the hydrothermal plume is difficult when it is more than 2,500 meters (about 8,200 feet) below Arctic sea ice or white crests of storm surges. The current study is the first to directly test whether the tops of these columns provide suitable habitat for Sulfurimonas.
Samples were taken in the central part of the Arctic Ocean, as well as in the southern part of the Atlantic Ocean.
Genome sequencing revealed one particular species, named Sulfurimonas pluma, that was “globally abundant and active in cold (below 0–4°C), oxygen- and hydrogen-rich hydrothermal plumes.”
Unlike other Sulfurimonas, the genome of S. pluma has shown signs of an aerobic metabolism that depends on oxygen for growth.
The bacteria also appear to have lost the ability to reduce nitrate, which this genus normally uses instead of oxygen, when living around hydrothermal vents.
More research is needed to find out which minerals and compounds promote the growth of S. pluma in semi-freezing columns of drifting material, but according to new data, this appears to be a suitable environment for bacteria to live and breed.
Other signs of bacteria inside hydrothermal plumes are thought to come from the surrounding seawater rather than hydrothermal vents. This may be true for S. pluma, but this bacterium may also be a “transitional” species. This could explain how some of the oldest life forms in the ocean (perhaps over 4 billion years old) evolved to move away from hydrothermal vents and settle elsewhere.
“We think that a hydrothermal plume not only disperses microorganisms from hydrothermal vents, but can also ecologically connect the open ocean to seafloor habitats,” Molari says. Our phylogenetic analysis indicates that S. pluma may be descended from a vent-related ancestor. got a higher resistance to oxygen, and then spread through the oceans.”
Mulari and colleagues say their findings have opened “new paradigms in the microbial ecology” of the sea, opening up a new niche for the many bacteria found in oceans around the world.
The study is published in the journal Nature Microbiology.
Source: Science Alert