The new findings provide insights into how life evolved on Earth.

A groundbreaking research contradicts the widely held belief that the majority of life in the ocean is powered by photosynthesis through sunlight, demonstrating that many ocean bacteria get their energy from hydrogen and carbon monoxide.

How bacteria thrive without sunlight at the darkest depths of the ocean has long been a mystery. According to a recent study by Monash University researchers that was published in the journal Nature Microbiology, the development of microorganisms at these extreme depths is fueled by a unique mechanism known as chemosynthesis, or growth using inorganic compounds.

The five-year research, coordinated by Dr. Rachael Lappan and Professor Chris Greening of the Biomedicine Discovery Institute, demonstrates that two common gases, hydrogen and carbon monoxide, provide fuel for billions of bacteria in the ocean from the tropics to the poles.

Professor Greening says that until now, most scientists thought that photosynthesis was the main source of energy for microorganisms in the ocean (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,” he comments.

“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.”

The research combined oceanic chemical measurements with laboratory analysis of microbial cultures, utilizing metagenomic sequencing to reveal “the genetic blueprint” of oceanic microbes. The team discovered that genes enabling hydrogen consumption exist across eight distinct microbial groups (phyla), and this survival strategy becomes increasingly prevalent with increasing ocean depth.

“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,” adds Dr. Lappan.

This experiment was motivated by the researchers’ earlier work on soil microbes. The majority of soil bacteria can survive by consuming hydrogen and carbon monoxide from the atmosphere, according to research by Professor Greening and colleagues.

“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,” adds Dr. Lappan.

These results offer a deeper understanding of the evolution of life.

“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,” concludes Professor Greening.

Source: 10.1038/s41564-023-01322-0

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