Nitrogen cycle to the moon

The discovery of bacteria that can turn urine into rocket fuel has, unsurprisingly, gotten a lot of media attention in recent weeks. But despite the slight exaggeration – NASA has given up the idea of flying to Mars on wee power any time soon – it’s actually a key component in a mechanism essential to supporting life in the ocean.

Nitrogen is an essential part of biology, making up substances like amino acids and DNA. However, despite the fact that it makes up 78% of the Earth’s atmosphere, its gaseous form, N2, is mostly inert and hard for plants and animals to use.

As a result, we rely on a complex series of chemical reactions, known as the nitrogen cycle, in which N2 is “fixed” by bacteria or chemical processes into a form we can use; and then, when we’ve finished with it, either through waste or decomposition, it’s turned back into nitrogen gas.

It’s this second part where the rocket fuel comes in: the nitrogen-containing waste product that comes from decomposition, or particularly, urine, is ammonium, NH4. In the deep oceans, where naturally there is no air, ammonium is turned back into N2 by a reaction called anaerobic ammonium oxidation, or anammox for short.

Marine nitrogen cycle, showing the role of anammox in turning ammonium into N2 in the deeper anoxic region (without oxygen)
Marine nitrogen cycle, showing the role of anammox in turning ammonium into N2 in the deeper anoxic region (without oxygen). PON stands for "particulate organic nitrogen", which includes phytoplankton; DON is "dissolved organic nitrogen"; and DNRA is, wait for it, "dissimilatory nitrate reductase to ammonium" (Image from Nature)

In a letter recently published in the journal Nature, scientists from Radboud University Nijmegen in the Netherlands have described the chemical mechanism used by bacteria that perform this anammox reaction. And an important part of it involves the chemical hydrazine, N2H4. And hydrazine happens to be a very unstable compound used in rocket fuel.

As I mentioned earlier, NASA has dismissed this as a way to travel to other planets using astronaut wee. But this is still a useful discovery, apart from the fact that it explains the production of 50% of the N2 released from the oceans.

Being anaerobic (that is, not needing oxygen), this reaction is useful for treating human waste. And potentially it means we could create other useful biofuels from sewage treatment.

Which might not quite be rocket fuel, but it’s nothing to piss on.

Kartal B, Maalcke WJ, de Almeida NM, Cirpus I, Gloerich J, Geerts W, Op den Camp HJ, Harhangi HR, Janssen-Megens EM, Francoijs K-J, Stunnenberg HG, Keltjens JT, Jetten MSM & Strous M 2011, “Molecular mechanism of anaerobic ammonium oxidation”, Nature, published online 02 October 2011, doi:10.1038/nature10453

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