Oxygen’s watery past

Oxygen’s watery past

4:55 PM, 17th August 2011
Oxygen’s watery past

 

CAMBRIDGE, US: Today, oxygen takes up a hefty portion of earth’s atmosphere: Life-sustaining O2 molecules make up 21 per cent of the air we breathe. However, very early in earth’s history, O2 was a rare player in the turbulent mix of primordial gases. It wasn’t until the “Great Oxidation Event” (GOE), nearly 2.3 billion years ago, when oxygen made any measurable dent in the atmosphere.

New MIT research suggests O2 may have been made on earth hundreds of millions of years in low quantities. The MIT researchers found evidence that tiny aerobic organisms may have evolved to survive on extremely low levels of the gas in  undersea oases in oceans.

In laboratory experiments, former MIT, Graduate Student, Jacob Waldbauer, working with Professor of Geobiology, Roger Summons and Dianne Newman, formerly of MIT’s Department of Biology and now at the California Institute of Technology, found that yeast, an organism that can survive with or without oxygen, is able to produce key oxygen-dependent compounds, even with only miniscule puffs of the gas.

The findings suggest that early ancestors of yeast could have been similarly resourceful, working with whatever small amounts of O2 may have been circulating in the oceans before the gas was detectable in the atmosphere. The team published its findings last week in the Proceedings of the National Academy of Sciences.

“The time at which oxygen became an integral factor in cellular metabolism was a pivotal point in earth history,” said Summons. “The fact that you could have oxygen-dependent biosynthesis very early on in the earth’s history has significant implications.”

Waldbauer and colleagues suggest that O2 was in fact present on Earth but in extremely low concentrations. To test their theory, they looked to modern yeast as a model. Yeast naturally uses O2, in combination with sugars, to synthesize ergosterol, its primary sterol. To find the lowest level of O2 yeast can consume, the team set up an experiment to identify the point at which yeast switches from anaerobic to aerobic activity.

Waldbauer and team found that without oxygen present, yeast happily took up sterol from the medium but made none from scratch. When Waldbauer pumped in tiny amounts of oxygen, a switch occurred in yeast. The scientists found that yeast are able to make steroids using small, nanomolar concentrations of O2, supporting the theory that oxygen, may have indeed been around long before the gas made an appearance in the atmosphere.

Waldbauer and Summons surmise that oxygen production and consumption may have occurred in the oceans for hundreds of millions of years before the atmosphere saw even a trace of the gas. “We know all kinds of biology happens without any O2 at all,” said Waldbauer. “But it’s quite possible there was a vigorous cycle of O2 happening in some places and other places it might have been completely absent.”

© Massachusetts Institute of Technology News 

 

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