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Scientists at the Danish National Environmental Research Institute (NERI) and the University of Aarhus are the leaders of an international research team that is presenting ground-breaking news this week in the renowned journal Nature. These researchers have found small animals on the sea floor that breathe nitrate instead of oxygen. This means the textbooks will have to be rewritten – as regards both the nitrogen cycle and the ability of animals to survive without oxygen.
Shells of the three species of foraminifera that have so far been revealed as breathers of nitrate. The white pins measure 1/10 mm. Each species has its own characteristic type of shell, which can be preserved as a fossil for millions of years. . a: Globobuliminap seudospinescens. b:Nonionella cf. Stella. c : Stainforthia sp.
Life without oxygen
Foraminifera are single-celled animals (protozoa) surrounded by a shell of varying size and form. They are found in vast numbers on sea beds all over the world. The scientists have now discovered that some foraminifera can breathe nitrate when they inhabit environments with no oxygen.
Foraminifera can gather an enormous stock of nitrate close to the surface of the sea floor. Filled up with nitrate, these organisms can live deeper down in the sea bed, where there is plenty of food and there are very few predators. In this oxygen-free environment, they breathe nitrate and can thus – in a manner of speaking – hold their breath for weeks.
How higher-order organisms like foraminifera have become capable of breathing nitrate remains a mystery. The solution will have to await the numerous investigations that will now be put in motion on the basis of this new discovery.
New understanding of the nitrogen cycle
The research team – led by Nils Risgaard-Petersen from NERI – has demonstrated that foraminifera breathe the same way known for years from bacteria, which remove nitrate-nitrogen by the process of denitrification. These bacteria are actively used in wastewater treatment plants and wetlands to reduce the nitrate pollution stemming from urbanisation and land cultivation.
This means the process itself is not new. However, the fact that animals can breathe nitrate is a ground-breaking discovery, which immediately raises new questions. How many animals can breathe and live the same way? Are they important enough that our understanding of the global nitrogen balance needs to be revised?
Just five years ago, Danish scientists from institutions including NERI revealed that a totally unheeded bacterial process called anammox also removes large amounts of nitrogen from the environment. What we learned at school about how nitrogen circles the earth is being put to the test at present, and scientists are convinced that new discoveries are just round the corner.
A mass of live foraminifera, caught on a brush and ready for further investigations. Some will be used for measuring their breathing of nitrate, others will be analysed for their nitrate content, and the rest will be preserved for determining the species.
Searching for oil
Geologists belong to the group of people who are particularly interested in the new discovery. Foraminifera shells are actually important clues that provide information about the environment and climate changes that have taken place over several hundred million years. The ancient shells – the fossils – indicate places where it is worth drilling for oil and other resources. And with new knowledge about the lifestyle of the foraminifera, geologists will be better able to decipher the clues left by these organisms.
Continues on the Galathea Expedition
On the Danish Galathea Expedition – which has just sailed from Denmark to begin an 8 month scientific expedition – the Danish scientists will continue their hunt around the world for new animals and bacteria that breathe nitrate.
The search for more animals that breathe nitrate has already begun. One obvious place is the Danish Limfjord – a stretch of water often plagued by oxygen depletion – where biology students here are searching the harbour at Roenbjerg.
Further information:
Senior Scientist Nils Risgaard-Petersen, tel +45 8920 1400, nri@dmu.dk,
(not available 4–10 September 2006)
Associate Professor Lars Peter Nielsen, University of Aarhus, tel +45 8942 3250, lars.peter.nielsen@biology.au.dk
Risgaard-Petersen N, Alexandra M. Langezaal, Signe Ingvardsen, Markus C. Schmid, Mike S. M. Jetten, Huub J. M. Op den Camp, Jan W. M. Derksen, Elisa Piña-Ochoa, Susanne P. Eriksson, Lars Peter Nielsen, Niels Peter Revsbech, Tomas Cedhagen & Gijsbert J. van der Zwaan (2006). Evidence for complete denitrification in a benthic foraminifer. Nature 447 :93-96
High resolution photographs for download
Danish version
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