Really Strange Stuff Lurks At The Deepest Point Of The World's Ocean

Overhead view of ROV sampling at the erupting NW Rota-1 volcano. NOAA/PMEL

How does anything, even a tiny microbe, survive in the pitch-black depths of the world’s deepest sea trench with a crushing 10,000 meters (32,800 feet) of water towering above them?

For the millions of microbial cultures living in this alien environment, the only way to get your energy is by chomping down on hydrocarbons. In fact, these oddball bacteria can actually live off petroleum and other hydrocarbon fuel sources.

A new study, published today in the open access journal Microbiome, by the Ocean University of China has taken a deep dive into the world of microbes living at the bottom of the Mariana Trench, the world’s deepest sea trench in the western Pacific Ocean, and also analyzed their genes. 

Samples of water were captured in specially designed flasks right at the trench's deepest known point, the Challenger Deep, at levels as deep as 9,898 to 10,916 meters (32,473 to 35,813 feet). The microbes of this environment are scarcely understood, so this is the most in-depth study of its kind to date. 

The findings show this deep seabed is caked in genera of bacteria known to consume hydrocarbons, such as Oleibacter, Thalassolituus, and Alcanivorax. In fact, proportions of Oceanospirillales bacteria are higher than anywhere else on Earth. Genetic analysis of the deep-sea inhabitants also showed that they shared many genes with oil-degrading bacteria that were observed in Deepwater Horizon oil spills halfway across the world in the Gulf of Mexico.

“The bacteria we found are similar to those of the Deepwater Horizon spill, the 2010 oil spill in the Gulf of Mexico,” Xiao-Hua Zhang, study author and microbial oceanographer at the Ocean University of China, told IFLScience.

“They could play a role in consuming petroleum oil,” they added. “These bacteria showed high hydrocarbon degradation activity, and thus may play important roles in cleaning up oil spilled into the ocean, especially that sink to the deep water.”

Most ocean life fundamentally relies on the photosynthetic activities of phytoplankton and plants to first harness energy from sunlight. But below 200 meters (656 feet) of seawater, only insignificant levels of light can be found. Deeper than 1,000 meters (3,280 feet) and the environment is pitch black. Life, therefore, must find another source of energy and nutrition. 

For these bacteria, it is the consumption of hydrocarbons. However, as the study authors note, it’s still unclear how these bacteria obtain their meals. Are they naturally occurring in the seabed’s sediments or, perhaps even more intriguingly, are these abundant bacteria colonies feasting on petroleum?

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