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Biochemistry

Microbes can munch nitric oxide

Findings suggest how life managed before oxygen was plentiful in the atmosphere

by Laura Howes
March 25, 2019

 

A microscopy image of K Stuttgartiensis.
Credit: Laura van Niftrik
Kuenenia stuttgartiensis, here seen under a transmission electron microscope, can live on nitric oxide.

Back when the Earth and life on it were young, the atmosphere was very different. There wasn’t a lot of oxygen around, but there was nitric oxide. Now, a team of researchers in the Netherlands and Germany report a bacterium that can grow using just NO as an oxidizing species. The species, Kuenenia stuttgartiensis,might be the first bacterium known to survive on NO, and at concentrations that would kill other bacteria. The findings, researchers say, have implications for understanding the evolution of life on young Earth.

Boran Kartal started studying K. stuttgartiensis when he was at Radboud University in the Netherlands. The bacterium is a freshwater species and is also found in wastewater treatment plants. Kartal had determined that the species was involved in emitting dinitrogen into the atmosphere via a process known as anammox, or anaerobic ammonium oxidation, which converts NO2 to NO and then combines the NO with ammonium to produce N2. Now at the Max Planck Institute in Bremen, Germany, but still working with his Dutch colleagues, Kartal decided to explore whether microbes could use NO to grow instead of NO2. The answer for K. stuttgartiensis is yes (Nat. Commun. 2019 DOI: 10.1038/s41467-019-09268-w).

“These findings change our understanding of the Earth’s nitrogen cycle,” Kartal says. “Nitric oxide is primarily thought of as a toxin, but now we show that anammox can make a living from converting NO to N2.”

Because NO depletes the ozone layer and N2O is a potent green house gas, Kartal suggests that these findings could have implications for the climate and atmospheric N2 production. However, Sara Hallin at the Swedish University of Agricultural Science thinks the discovery is most interesting from an evolutionary perspective, suggesting a metabolic pathway that was possible on early Earth before more oxidized species existed.

Kartal thinks that other anammox bacteria might be able to use NO as an oxidizing agent. His group is now on the hunt for more microorganisms, and therefore enzymes, that can use NO directly.

CORRECTION:

This story was updated on March 27, 2019, to correct the explanations that anammox bacteria convert NO2 to NO when producing N2 and that N2O is a potent greenhouse gas.

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