Evidence for complete denitrification in a benthic foraminifer |
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Authors: | Risgaard-Petersen Nils Langezaal Alexandra M Ingvardsen Signe Schmid Markus C Jetten Mike S M Op den Camp Huub J M Derksen Jan W M Piña-Ochoa Elisa Eriksson Susanne P Nielsen Lars Peter Revsbech Niels Peter Cedhagen Tomas van der Zwaan Gijsbert J |
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Affiliation: | Department of Marine Ecology, National Environmental Research Institute, Vejls?vej 25, DK-8600 Silkeborg, Denmark. nri@dmu.dk |
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Abstract: | Benthic foraminifera are unicellular eukaryotes found abundantly in many types of marine sediments. Many species survive and possibly reproduce in anoxic habitats, but sustainable anaerobic metabolism has not been previously described. Here we demonstrate that the foraminifer Globobulimina pseudospinescens accumulates intracellular nitrate stores and that these can be respired to dinitrogen gas. The amounts of nitrate detected are estimated to be sufficient to support respiration for over a month. In a Swedish fjord sediment where G. pseudospinescens is the dominant foraminifer, the intracellular nitrate pool in this species accounted for 20% of the large, cell-bound, nitrate pool present in an oxygen-free zone. Similarly high nitrate concentrations were also detected in foraminifera Nonionella cf. stella and a Stainforthia species, the two dominant benthic taxa occurring within the oxygen minimum zone of the continental shelf off Chile. Given the high abundance of foraminifera in anoxic marine environments, these new findings suggest that foraminifera may play an important role in global nitrogen cycling and indicate that our understanding of the complexity of the marine nitrogen cycle is far from complete. |
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