The balance between methane-producing and -consuming processes has a major effect on the worldwide emission of this strong greenhouse gas into our atmosphere. The team of microbiologists and biogeochemists now discovered an archaeon – the other branch of ancient prokaryotes besides bacteria – of the order Methanosarcinales that uses iron to convert methane into carbon dioxide. One of the bioreactors, in which Kartal and his colleagues found the rust-munching microbes.
Besides, these archaea have another trick up their sleeve. They can turn nitrate into ammonium: the favourite food of the famous anammox bacteria that turn ammonium into nitrogen gas without using oxygen. “This is relevant for wastewater treatment”, says Boran Kartal, a microbiologist who recently moved from Radboud University to the Max Planck Institute in Bremen.
Closer than expected
While there have been numerous indications that such iron-dependent methane oxidizers existed, researchers have never been able to isolate them. Surprisingly, they were right in front of our doorstep: “After years of searching, we found them in our own sample collection”, says microbiologist Mike Jetten of Radboud University with a smile. “We eventually discovered them in enrichment cultures from the Twentekanaal in The Netherlands that we’ve had in our lab for years.”
“Based on the genetic blueprint of these microorganisms”, Kartal adds, “we hypothesized that they could convert particulate iron – basically rust – coupled to methane oxidation. So we tested our hypothesis in the lab – and these organisms did the trick.” In the next step, Kartal wants to look closer into the details of the process. “These findings fill one of the remaining gaps in our understanding of anaerobic methane oxidation. Now we want to further investigate which protein complexes are involved in the process.”
Billions of years ago
The newly discovered process could also lead to new insights into the early history of our planet. Already 4 to 2.5 billion years ago, Methanosarcinalesarchaea might have abundantly thrived under the methane-rich atmosphere in the ferruginous (iron holding) Archaean oceans,. More information on the metabolism of this organism can therefore shed new light on the long-standing discussion of the role of iron metabolism on early earth.
Contacts and sources:
Dr. Boran Kartal
Max Planck Institute for Marine Microbiology, Bremen