Evidence has suggested chemosynthesis may have more significance in the development of deep ocean microbes than previously thought

The deep sea continues to be a mystery to scientists, with only 5% of our oceans having been explored as of 2022. The way life continues to thrive so deep within our oceans is a key question that’s puzzled researchers for decades, “But what about those regions so deep that light can’t penetrate?” pointed out Professor Chris Greening.

Through conducting a five-year study, leaders Dr Rachael Lappan and Professor Greening from the Biomedicine Discovery Institute have revealed that two common gases – hydrogen and carbon monoxide – serve as the fuel for trillions of deep ocean microbes.

Chemosynthesis and the survival of deep ocean microbes

The study combined chemical measurements taken on oceanic voyages with a laboratory-based characterisation of microbial cultures. By using metagenomic sequencing, the team were able to find “the genetic blueprints of all of the microbes present in a given region of the ocean,” according to Dr Lappan.

According to the team, “Hydrogen and carbon monoxide in fact “fed” microbes in all regions we’ve looked at: from urban bays to around tropical islands to hundreds of metres below the surface. Some can even be found beneath Antarctica’s ice shelves.”

Hydrogen and carbon monoxide fed microbes

Chemosynthesis is the process through which glucose is made by bacteria using chemicals as the primary energy source instead of sunlight. Through this 5-year mission Professor Greening and their team were able to show that “chemosynthesis is dominant” in the deep ocean.

Dr Lappan explained how “The genes that enable hydrogen consumption across eight distantly related types of microbes, known as phyla, and this survival strategy becomes more common the deeper they live.”

Feeding soil bacteria and deep ocean microbes with hydrogen and carbon monoxide

For this project, the researchers were inspired by their previous work on soil bacteria.

In recent years Professor Greening and colleagues were able to prove how most soil bacteria can live by consuming hydrogen and carbon monoxide from the atmosphere.

“The surface layers of the world’s oceans generally contain high levels of dissolved hydrogen and carbon monoxide gases due to various geological and biological processes. So it made sense that oceanic bacteria used the same gases as their terrestrial cousins,” Dr Lappan said.

So it made sense that oceanic bacteria used the same gases as their terrestrial cousins

These findings provide insights into how life evolved. Professor Greening concluded that “The first life probably emerged in deep-sea vents using hydrogen, not sunlight, as the energy source. It’s incredible that, 3.7 billion years later, so many deep ocean microbes are still using this high-energy gas and we’ve completely overlooked this until now.”


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