Mysterious microbes bubble up into the ocean floor

Millions of microbes are buried in sediments deep beneath the ocean, and a new study has revealed that some of them bubble up to seafloor with fluids from buried petroleum reservoirs. After seeping up into the deep sea, the microbes diversify microbial communities and influence ocean processes, such as carbon cycling. 

Bacteria, viruses, and other organisms that are hidden from sight play a central role in regulating Earth’s functions and resources. An estimated one-third of these microbes exist deep below the seafloor.

Study co-author Emil Ruff is a scientist at the Marine Biological Laboratory (MBL). 

“This study confirms that petroleum seeps are a conduit for transporting life from the deep biosphere to the seafloor,” said Ruff.

The analysis was focused on 172 seafloor sediment samples from the eastern Gulf of Mexico that had been collected as part of a 2011 survey for the oil industry. 

The team used metagenomic techniques to determine what microbes were present in the sediment samples, and sequenced the genomes of the most interesting organisms to investigate what their activity may be like in the subsurface.

Some of the samples contained migrated gaseous hydrocarbons, which are the main components of oil and gas. These petroleum seeps harbored distinct microbial communities containing bacteria and archaea that are known to thrive in deep biosphere sediments.

The study was led by Anirban Chakraborty and Casey Hubert of the University of Calgary.

“Whereas sedimentation slowly buries microbial communities into the deep biosphere, these results show that it’s more of a two-way street. The microbes coming back up offer a window to life buried deeper below,” said Hubert. 

“These relatively accessible surface sediments give us a glimpse into the vast, subsurface realm.”

The research is providing new insight into the metabolic diversity of seabed petroleum seep microbial communities. “If it weren’t for the microbes living at hydrocarbon seeps, the oceans would be full of gas and oil,” said Chakraborty.

Explorations of deep-sea ecosystems are often limited by the number and quality of samples because the seafloor is difficult to access. 

“One of the strengths of this study is the large number of samples analyzed, allowing robust statistical inferences of the microbes present in the petroleum seeps,” explained Ruff. 

The study is published in the Proceedings of the National Academy of Sciences.

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By Chrissy Sexton, Earth.com Staff Writer