title: Evidence for complete denitrification in a benthic foraminifer.
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.
authors.affiliation: Department of Marine Ecology, National Environmental Research Institute, Vejlsøvej 25, DK-8600 Silkeborg, Denmark. nri@dmu.dk
authors.forename: Nils
authors.initials: N
authors.lastname: Risgaard-Petersen
authors.forename: Alexandra M
authors.initials: AM
authors.lastname: Langezaal
authors.forename: Signe
authors.initials: S
authors.lastname: Ingvardsen
authors.forename: Markus C
authors.initials: MC
authors.lastname: Schmid
authors.forename: Mike S M
authors.initials: MS
authors.lastname: Jetten
authors.forename: Huub J M
authors.initials: HJ
authors.lastname: Op den Camp
authors.forename: Jan W M
authors.initials: JW
authors.lastname: Derksen
authors.forename: Elisa
authors.initials: E
authors.lastname: Piña-Ochoa
authors.forename: Susanne P
authors.initials: SP
authors.lastname: Eriksson
authors.forename: Lars Peter
authors.initials: LP
authors.lastname: Nielsen
authors.forename: Niels Peter
authors.initials: NP
authors.lastname: Revsbech
authors.forename: Tomas
authors.initials: T
authors.lastname: Cedhagen
authors.forename: Gijsbert J
authors.initials: GJ
authors.lastname: van der Zwaan
mesh_terms: D000693:Anaerobiosis; D001105:Archaea / Q000235:genetics; D002677:Chile; D005057:Eukaryotic Cells / Q000378:metabolism* / Q000648:ultrastructure; D019015:Geologic Sediments / Q000737:chemistry; D009573:Nitrites / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D013548:Sweden
chemical_list: D009573:Nitrites; D009584:Nitrogen; D010100:Oxygen