SCT: Rocket Science in a Microbe Saves the Planet
A molecular machine in specialized
bacteria uses rocket fuel to complete
the nitrogen cycle, vital to all life
This article was originally published in Science & Culture Today.
Rocket Science in a Microbe Saves the Planet
by David F. Coppedge
Science & Culture Today, November 23, 2015
reprinted April 13, 2022
Anammox. It’s a good term to learn. Wikipedia‘s first paragraph stresses its importance:
Anammox, an abbreviation for ANaerobic AMMonium OXidation, is a globally important microbial process of the nitrogen cycle. The bacteria mediating this process were identified in 1999, and at the time were a great surprise for the scientific community. It takes place in many natural environments… [Emphasis added.]
And now, the news. A team of European scientists found something very interesting about the bacteria. Publishing in Nature, the researchers tell how they have ascertained the structure of a molecular machine that performs chemical wizardry using rocket science.
Anaerobic ammonium oxidation (anammox) has a major role in the Earth’s nitrogen cycle and is used in energy-efficient wastewater treatment. This bacterial process combines nitrite and ammonium to form dinitrogen (N2) gas, and has been estimated to synthesize up to 50% of the dinitrogen gas emitted into our atmosphere from the oceans. Strikingly, the anammox process relies on the highly unusual, extremely reactive intermediate hydrazine, a compound also used as a rocket fuel because of its high reducing power. So far, the enzymatic mechanism by which hydrazine is synthesized is unknown. Here we report the 2.7 resolution crystal structure, as well as biophysical and spectroscopic studies, of a hydrazine synthase multiprotein complex isolated from the anammox organism Kuenenia stuttgartiensis. The structure shows an elongated dimer of heterotrimers, each of which has two unique c-type haem-containing active sites, as well as an interaction point for a redox partner. Furthermore, a system of tunnels connects these active sites. The crystal structure implies a two-step mechanism for hydrazine synthesis: a three-electron reduction of nitric oxide to hydroxylamine at the active site of the ?-subunit and its subsequent condensation with ammonia, yielding hydrazine in the active centre of the ?-subunit. Our results provide the first, to our knowledge, detailed structural insight into the mechanism of biological hydrazine synthesis, which is of major significance for our understanding of the conversion of nitrogenous compounds in nature.
Dinitrogen gas (N2) is a tough nut to crack. The atoms pair up with a triple bond, very difficult for humans to break without a lot of heat and pressure. Fortunately, this makes it very inert for the atmosphere, but life needs to get at it to make amino acids, muscles, organs, and more. Nitrogenase enzymes in some microbes, such as soil bacteria, are able break apart the atoms at ambient temperatures (a secret agricultural chemists would love to learn). They then “fix” nitrogen into compounds such as ammonia (NH3) that can be utilized by plants and the animals that eat them. To have a nitrogen cycle, though, something has to return the N2 gas back to the atmosphere. That’s the job of anammox bacteria.
Most nitrogen on earth occurs as gaseous N2 (nitrogen oxidation number 0). To make nitrogen available for biochemical reactions, the inert N2 has to be converted to ammonia (oxidation number -III), which can then be assimilated to produce organic nitrogen compounds, or be oxidized to nitrite (oxidation number +III) or nitrate (+V). The reduction of nitrite in turn results in the regeneration of N2, thus closing the biological nitrogen cycle.
Let’s take a look at the enzyme that does this, the “hydrazine synthase multiprotein complex.” Rocket fuel; imagine! No wonder the scientific community was surprised. The formula for hydrazine is N2H4. It’s commonly used to power thrusters on spacecraft, such as the Cassini Saturn orbiter and the New Horizons probe that went by Pluto recently. Obviously, the anammox bacteria must handle this highly reactive compound with great care….
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See also: How Microbes Make Earth Habitable.
David Coppedge, B.S. Education, B.S. Physics, founded Creation-Evolution Headlines in late 2000 as a way to share science news he was encountering at NASA. It has grown into a highly-trusted source of news and commentary critical of the pro-Darwin consensus, providing analysis of breaking news of interest to creationists and evolutionists, without the Darwin spin. He has authored over 7,000 entries at CEH since its inception.