Microbes produce oxygen in the dark

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Beate Kraft, biologist, University of Southern Denmark. Credit: Jacob Fredegaard Hansen, SDU

There is more going on in the deep, dark waters of the ocean than you might think: Countless numbers of invisible microorganisms live their daily lives in water columns, and now researchers have found that some ‘between them produce oxygen in an unexpected way.

The study is led by Beate Kraft and Donald E. Canfield of the University of Southern Denmark and published in the journal Science. Contributing authors are Nico Jehmlich, Morten Larsen, Laura Bristow, Martin Könneke and Bo Thamdrup. Beate Kraft is Assistant Professor in the Department of Biology. She focuses on microbial physiology and biochemistry, and her research is funded by a Villum Young Investigator grant. Don E. Canfield is Professor of Ecology in the Department of Biology and Chair of Biology at the Danish Institute for Andvance Study.

Oxygen is vital for life on Earth and is produced primarily by plants, algae and cyanobacteria through photosynthesis. A few microbes are known to make oxygen without sunlight, but so far they have only been found in very limited quantities and in very specific habitats.

Enter the ocean-living microbe Nitrosopumilus maritimus and its cousins, called ammonia oxidizing archaea.

Phantom organisms that hang out in the dark

“These types are really abundant in the oceans, where they play an important role in the nitrogen cycle. For this, they need oxygen, which is why they are also very abundant in waters where there is no oxygen, says biologist Beate Kraft. “We figured they were just hanging out there with no function; they must be some kind of phantom cells.

But there was something astonishing about it: “These microbes are so common that one in five cells in a bucket of seawater is one of them,” adds Don Canfield, co-author of the article.

So the researchers got curious; could they have a function in oxygen-depleted water after all?

They make their own oxygen

Microbes produce oxygen in the dark

Beate Kraft and her research team study water samples, University of Southern Denmark. Credit: Jacob Fredegaard Hansen / University of Southern Denmark

Beate Kraft decided to test them in the lab. “We wanted to see what would happen if they ran out of oxygen, like they do when they switch from oxygen-rich water to oxygen-depleted water. Would they survive?

“We saw how they used up all the oxygen in the water, and then to our surprise, within minutes the oxygen levels started to rise again. It was very exciting, ”says Don Canfield.

Enough for me and my friends

Nitrosopumilus maritimus has been shown to be able to produce oxygen in a dark environment. Not much, not at all to the point of influencing oxygen levels on Earth, but enough to sustain itself.

“If they produce a little more oxygen than they need, it will be quickly taken up by other organisms in their vicinity, so that oxygen will never leave the ocean,” says Beate Kraft.

But what effect do they have on the environment in which they live, these extremely abundant oxygen-producing microbes?

New oceanic expedition

Researchers already knew that ammonia-oxidizing archaea are microorganisms that maintain the global nitrogen cycle, but they were unaware of the extent of their capabilities.

In the newly discovered pathway, Nitrosopumilus maritimus couples the production of oxygen with the production of nitrogen gas. In doing so, they remove bioavailable nitrogen from the environment.

“If this lifestyle is prevalent in the oceans, it certainly forces us to rethink our current understanding of the marine nitrogen cycle,” says Kraft. “My next step is to investigate the phenomenon that we have observed in our laboratory cultures in oxygen-depleted waters in various oceanic locations around the world. “

His research team has already collected samples from the Mariager Fjord in Denmark, and the next stop is the waters off Mexico and Costa Rica.


Sea ice prevented oxygen from reaching the depths of the ocean during the last ice age


More information:

Beate Kraft, Production of oxygen and nitrogen by an ammonia oxidizing archaeon, Science (2022). DOI: 10.1126 / science.abe6733. www.science.org/doi/10.1126/science.abe6733

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University of Southern Denmark


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Microbes produce oxygen in the dark (2022, January 6)
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