Sunday, February 1, 2015

Below the bottom of the sea, a third of our planet's biomass breathes sulfate

A massive group of sulfate-breathing microbes, potentially representing a third of all the life on our planet, has been identified living below the ocean floor.

It’s an amazing finding led largely by researchers at the University of Hawai`i, and it adds a whole new wrinkle to the study of how carbon is cycled on and in the planet. 

(To collect samples beneath the seafloor more than a mile and a half below the ocean’s surface, the GeoMicrobe [box at left], developed at the University of Hawaii Manoa, was hooked into the Circulation Obviation Retrofit Kit [CORK] observatory [right]. Credit:  Deep Submergence Group, Woods Hole Oceanographic Institution.)

The finding was reported in the journal Frontiers in Microbiology.

The authors are Alberto Robador, Sean P. Jungbluth, Douglas E. LaRowe, Robert M. Bowers, Michael S. RappĂ©, Jan P. Amend and the late James P. Cowen. They represent the University of Hawai`i’s NASA Astrobiology Institute, the Hawaii Institute of Marine Biology and the Department of Oceanography at the School of Ocean and Earth Science and Technology, as well as the Department of Earth Sciences and Department of Biological Sciences at the University of Southern California, Los Angeles.

The partnership that led to these discoveries was announced in 2010

The team dug two boreholes in the ocean floor, careful to seal them to prevent contamination from ocean water, and collected samples from the vast aquifer that exists under the bottom of the sea.

Why look there? “The basaltic ocean crust is the largest aquifer system on Earth, yet the rates of biological activity in this environment are unknown,” the authors write.

When they went looking, they found there’s lots of biological life there—a wide array of life forms in an area that characteristically does not have enough oxygen to support ocean life as we commonly recognize it. The organisms “breathe” using a process called sulfate reduction.

They are able to use the sulfate-rich water to break down carbon-based material that drops to the ocean floor with the death of marine life—algae, whales, fish and do forth.

“This is the first direct account of microbial activity in these type of environments, and shows the potential of these organisms to respire organic carbon,” said lead author Robador said in a press release.

It’s a good thing they issued the press release, because with due respect to the authors, when they’re writing for each other, it’s not as if most folks can even understand them: 

“Our sulfate-reduction rate measurements and sulfate-reducing microbial community analysis are indicative of the metabolic potential and broad dispersal of organotrophic sulfate-reducing microbial groups along fluid flow paths within deeply buried basaltic crust with significant implications for the marine carbon cycling.”

The researchers used DNA sequencing to study the life forms they found, most of which have not yet been described. 

“It’s a massive biome dominated by microbes that scientists know very little about,” says a University of Hawai`i press release. 

Because there is so much of it, it apparently plays a significant role in the planet’s carbon cycle, and getting a better understanding of it can help us understand how the Earth works.

“This is very exciting work that links rates of microbial activity to novel groups of microorganisms, particularly because we are combining cutting edge molecular biology techniques with samples collected from a part of our planet that is less accessible than outer space,” said University of Hawai`i researcher Jungbluth in another press release.

In the words of the study itself: “Our estimates suggest that microbially-mediated sulfate reduction may account for the removal of organic matter in fluids within the upper oceanic crust and underscore the potential quantitative impact of microbial processes in deep subsurface marine crustal fluids on marine and global biogeochemical carbon cycling.”

© Jan TenBruggencate 2015

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