For most of life on Earth, oxygen is essential & sunlight is generally needed to produce oxygen. But in an exciting twist, researchers have captured a common ocean deelling microbe that breaks all the rules.
Scientists have discovered that a microbe called Nitrosopumilus maritimus & many of its cousins, called ammonia-oxidizing archaea (AOA), are able to survive in dark, oxygen depleted environments by producing oxygen themselves. They do this using a biological process that has never been seen before.
Although it has been previously established that these microbes can live in environments where oxygen is scarce, what is not clear is what they get-up-to there and how they stay alive for as long as they do. This was the inspiration behind this new research.
“These are really abundant in the oceans, where they play an important role in nitrogen cycle,” explains microbiologist Beate Kraft of the University of Southern Denmark.
“To do this, they need oxygen, so it has long been a mystery why they are so abundant in waters where is no oxygen. We thought they were just hanging around there without any function? Are they like of ghost cells?
Collect a bucket of seawater from the ocean & one in five cells will be one of these organisms – that’s how common they are. Here, the researchers removed the microbes from their natural habitat & transfer them to the laboratory.
The team wanted to take a closer look at what would happen when all the available oxygen was gone and there was no-sunlight to produce new oxygen. The same scenario occurs when N.maritimus switches from oxygen-rich to oxygen-depleted waters.
What they found was something unexpected: the microorganisms were producing their own oxygen to create nitrite, with nitrogen gas as a by-product.
“We saw how they were using up all the oxygen in water, and then, to our surprise, within minutes the oxygen levels started to rise again,” says geobiologist Don Canfield from University of Southern Denmark. “It was very exciting.
At the moment, the researchers don’t know how the microbes do this trick, and the amount of oxygen produced appears to be relatively small (just enough for their own survival), but it appears to be different from the few oxygen with no sunlight processes that we already know.
What the new path shows is that the oxygen production of N. maritimus is linked to its production of nitrogen gas. Microbes somehow convert ammonia (NH3) to nitrite (NO2) – a process they use to metabolize energy – in an oxygen depleted environment.
In turn, it forces them to create its oxygen, that the team detected traces of, along with the nitrogen gas by-product.
This process removes bioavailable nitrogen from environment – and it’s a new wrinkle in the nitrogen cycle, which under-pins all ecosystems. This discovery could have “far-reaching” consequences and this requires further investigation.
“While this lifestyle is prevalent in the oceans, it definitely forces us to rethink our current understanding of the marine nitrogen cycle,” says Kraft.
“My next step is to study the phenomenon that we have observed in our laboratory cultures in low-oxygen water at various ocean locations around the world.
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