Ancient microbes found beneath ocean crust

Ancient microbes found beneath ocean crust

Two miles below the surface of the ocean, particularly in undersea aquifers, researchers have discovered a species of unclassified microbes that “breathe in” sulfate in absence of oxygen.

A joint study by researchers from University of Southern Carolina and University of Hawaii took samples from massive undersea aquifers under the Juan de Fuca Ridge, just off the coast of Washington State. Previous researchers have already drilled into that particular ocean floor to place underwater laboratories.

The samples were microbes that seemingly “breathe in” sulfate. Like any other microbes found on land or elsewhere, these samples break down organic compounds. However, instead of breaking down leaf litter or dead organisms, they break down organic compounds from dead fish and algae that sink to the sea bottom.

But the undersea aquifer lacks ample oxygen supply for anaerobic respiration. Thus, the samples use sulfate to obtain energy by reacting it with any carbon-containing compounds.

There are other species of microbes found elsewhere, including marshes and hydrothermal vents. Otherwise known as sulfur-reducing bacteria, these microbes have existed since 3.5 billion years ago. They are nonetheless among the oldest organisms in Earth.

Obtaining the samples were a challenging task, nonetheless. This fact also goes to any research involving undersea aquifers.

Note that undersea aquifers are networks of fresh water channels within porous rocks under the ocean floor. These aquifers are thought to comprise about one-third of the Earth’s biomass. Much of undersea aquifers remain uncharted

“Trying to take a sample of aquifer water without contaminating it with regular ocean water presented a huge challenge,” said Jan Amend, professor at USC Dornsife and director of the Center for Dark Energy Biosphere Investigations (C-DEBI), which helped fund the research.

To address the challenge, C-DEBI created a cork-like device called Circulation Obviation Retrofit Kit that helps in drilling ocean floors while also creating a seal. The device effectively keeps ocean water out thereby allowing researchers to deploy instruments and other devices for sampling and observation.

Ancient microbes found beneath ocean crust

The obtained microbial samples from the Juan de Fuca Ridge could nonetheless open a better understanding of carbon cycle as it transpires globally. Because the microbial samples use sulfur to break down carbon-based compounds from dead sea organisms, they subsequently release carbon dioxide. This process now adds to the overall carbon cycle that includes consumption of CO2 by plants, exhalation of animals, and absorption in the ocean.

“This is the first direct account of microbial activity in these environments, and shows the potential of these organisms to respire organic carbon,” said Alberdo Robador, lead author of the research and postdoctoral researcher at the USC Dornsife College of Letters, Arts and Sciences.

The complete findings of the research are in the paper “Activity and phylogenetic diversity of sulfate-reducing microorganisms in low-temperature subsurface fluids within the upper oceanic crust” and published in 2015 in the open-access journal Frontiers in Microbiology.