Biochemical controls: oxygen without photosynthesis (Introduction)

by David Turell , Monday, July 17, 2023, 16:52 (493 days ago) @ David Turell

By a different system deep underground:

https://www.quantamagazine.org/underground-cells-make-dark-oxygen-without-light-20230717/

"In groundwater reservoirs 200 meters below the fossil fuel fields of Alberta, Canada, they discovered abundant microbes that produce unexpectedly large amounts of oxygen even in the absence of light. The microbes generate and release so much of what the researchers call “dark oxygen” that it’s like discovering “the scale of oxygen coming from the photosynthesis in the Amazon rainforest,” said Karen Lloyd, a subsurface microbiologist at the University of Tennessee who was not part of the study. The quantity of the gas diffusing out of the cells is so great that it seems to create conditions favorable for oxygen-dependent life in the surrounding groundwater and strata.

“It is a landmark study,” said Barbara Sherwood Lollar, a geochemist at the University of Toronto who was not involved in the work. Past research has often looked at mechanisms that could produce hydrogen and some other vital molecules for underground life, but the generation of oxygen-containing molecules has been largely overlooked because oxygen seems so wedded to photosynthesis and the presence of light. Until now, “no study has pulled it all together quite like this one,” she said.

"The new study looked at deep aquifers in the Canadian province of Alberta, which has such rich deposits of underground tar, oil sands and hydrocarbon that it has been dubbed “the Texas of Canada.”

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"The researchers started identifying the microbes in the samples, using molecular tools to spot their telltale marker genes. A lot of them were methanogenic archaea — simple, single-celled microbes that produce methane after consuming hydrogen and carbon oozing out of rocks or in decaying organic matter. Also present were many bacteria that feed on the methane or on minerals in the water. (my bold)

"What didn’t make sense, however, was that many of the bacteria were aerobes — microbes that require oxygen to digest methane and other compounds. How could aerobes thrive in groundwaters that should have no oxygen, since photosynthesis is impossible? But chemical analyses found a lot of dissolved oxygen in the 200-meter-deep groundwater samples too.

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"While working in a lab in the Netherlands in the late 2000s, Strous noticed that a type of methane-feeding bacteria often found in lake sediments and wastewater sludges had a strange way of life. Instead of taking in oxygen from its surroundings like other aerobes, the bacteria created its own oxygen by using enzymes to break down the soluble compounds called nitrites (which contain a chemical group made of nitrogen and three oxygen atoms). The bacteria used the self-generated oxygen to split methane for energy.

"When microbes break down compounds this way, it’s called dismutation. Until now, it was thought to be rare in nature as a method for generating oxygen. Recent laboratory experiments involving artificial microbe communities, however, revealed that the oxygen produced by dismutation can leak out of the cells and into the surrounding medium to the benefit of other oxygen-dependent organisms, in a kind of symbiotic process. Ruff thinks that this could be what’s enabling entire communities of aerobic microbes to thrive in the groundwater, and potentially in the surrounding soils as well.

"The finding fills a crucial gap in our understanding of how the huge subterranean biosphere has evolved, and how dismutation contributes to the cycle of compounds moving through the global environment. The mere possibility that oxygen is present in groundwater “changes our understanding about the past, present and future of subsurface,” said Ruff, who is now an assistant scientist at the Marine Biological Laboratory in Woods Hole, Massachusetts.

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"Regardless of how important dismutation turns out to be elsewhere in the universe, Lloyd is astonished by how much the new findings defy preconceived notions about life’s needs, and by the scientific cluelessness they reveal about one of the planet’s biggest biospheres. “It’s as if we have had egg on our face all along,” she said."

Comment: life is everywhere, as amazing as it seems. Note my bold. Ancient Archaea from the start of life showed the way to make oxygen.