Cloudy material drifting from chimney-like vents in the ocean floor could harbor microscopic lifeforms that scientists didn’t even know existed.
Seabed ridges are littered with cracks called hydrothermal vents which spew hot, deep-Earth fluids containing hydrogen sulphides, methane and hydrogen into the ocean.
Around the warm periphery of these dynamic nutrient distributors huddle a host of hungry, mysterious microbes that use the chemicals released through the vent to thrive in the absence of sunlight Or plenty of oxygen.
But these may not be the only niches provided by vents in which microbes survive.
A new study has just identified a genus called Sulfurimonaswhich can not only thrive around hydrothermal vents, but also live in the colder, more oxygenated plumes that pour over them.
These smoky clouds can stretch upwards for hundreds of meters and miles. They occur when hot magma mixes with cold seawater and include an entirely different menu of chemicals from the hydrothermal vents from which they erupt.
Sulfurimonas is known to be a dominant player around hydrothermal vents, surviving easily in hot, oxygen-depleted water and using the sulfide emitted from the vents for energy, but these new findings suggest that some species have evolved to rise with the plumes.
Previous studies have sampled the tops of hydrothermal plumes and found genetic signs of Sulfurimonas, but the bacteria were not thought to actually grow in the cloud. The plumes were believed to be too cold and saturated with oxygen.
“We assumed that [the bacteria] were hunted there from environments associated with seafloor vents” explain marine microbiologist Massimiliano Molari from the Max Planck Institute in Germany.
“But we wondered if the plumes could actually be a suitable environment for some members of the Sulfurimonas band.”
Sampling hydrothermal plumes is a complicated job. This requires expeditions to remote regions of the ocean, where the boundaries of tectonic plates are gradually pulling apart.
These regions are not easy to locate, and even when found, sampling the hydrothermal plume is tricky when it is more than 2,500 meters (about 8,200 feet) below Arctic sea ice or white ice caps. choppy waves.
The current study is the first to directly test whether the tops of these plumes provide suitable habitat for Sulfurimonas.
Sampling took place in the central Arctic Ocean and also along the South Atlantic Ocean.
Genome sequencing revealed a particular species, called Sulfurimonas featherwhich was “globally abundant and active in cold (less than 0 to 4 degrees Celsius), oxygen-saturated, and hydrogen-rich hydrothermal plumes”.
Unlike other species of Sulfurimonas, S. plumaThe genome showed signatures of an aerobic metabolism, which relies on oxygen to thrive.
The bacterium also appears to have lost the ability to reduce nitrate, which the genus typically uses instead of oxygen when living around hydrothermal vents.
Further studies are needed to determine which metals and compounds promote S. plumain near-freezing plumes of drifting material, but according to the new findings, this appears to be an environment conducive to bacteria living and reproducing.
Other signs of bacteria in hydrothermal plumes are thought to come from the surrounding seawater and not from the hydrothermal vents. It might be true of S. pluma, but it could also be that this bacterium is a species “in transition”. This could explain how some of the oldest forms of ocean life (possibly over 4 billion years old) have evolved away from hydrothermal vents and settled elsewhere.
“We believe that the hydrothermal plume not only disperses microorganisms from hydrothermal vents, but may also ecologically connect the open ocean to seafloor habitats,” said Molari.
“Our phylogenetic analysis suggests that Sulfurimonas pluma could have derived from an ancestor associated with a hydrothermal vent, which acquired a greater tolerance for oxygen and then spread across the oceans.”
Molari and his colleagues say their findings opened “new paradigms in the microbial ecology” of the sea, revealing a new niche for an abundant bacterium found in oceans around the world.
The study was published in Natural microbiology.