How can deep ocean microbes survive without sunlight?

Scientists have long wondered how microbes growing in the deepest parts of the oceans can survive with no sunlight. Now, a team of researchers led by Monash University in Australia has shown that a distinct process called “chemosynthesis” (growth using inorganic compounds) fuels these microbes. More specifically, two common gases – hydrogen and carbon monoxide – serve as fuel for the trillions of microbes living in the depths of the oceans from the tropics to the poles.

Until recently, most scientists believed that ocean microbial life is also driven by photosynthesis (growth by using light energy). “But what about those regions so deep that light can’t penetrate or so nutrient-poor that algae can’t thrive? We showed in this study that instead chemosynthesis is dominant in these regions,” said study senior author Chris Greening, an expert in Microbiology at Monash. 

“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 meters below the surface. Some can even be found beneath Antarctica’s ice shelves.”

The researchers combined chemical measurements during ocean voyages with lab-based characterization of microbial cultures, as well as metagenomic sequencing (a method providing the genetic blueprints of all the microbes present in a specific region in the ocean). 

“We found 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,” reported lead author Racheal Lappan, a research fellow in Microbiology at Monash.

The study was inspired by previous work on soil bacteria which revealed that most of these terrestrial microorganisms can thrive 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,” Lappan explained.

The findings provide novel insights into how life on Earth evolved. “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 microbes in the oceans are still using this high-energy gas and we’ve completely overlooked this until now,” Greening concluded.

The study is published in the journal Nature Microbiology.

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By Andrei Ionescu, Earth.com Staff Writer

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