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View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Radboud Repository PDF hosted at the Radboud Repository of the Radboud University Nijmegen The following full text is a publisher's version. For additional information about this publication click this link. http://hdl.handle.net/2066/60185 Please be advised that this information was generated on 2017-12-06 and may be subject to change. AQUATIC MICROBIAL ECOLOGY Vol. 36: 293–304, 2004 Published September 14 Aquat Microb Ecol Anaerobic ammonium oxidation in an estuarine sediment Nils Risgaard-Petersen1,*, Rikke Louise Meyer2, Markus Schmid3, Mike S. M. Jetten4, Alex Enrich-Prast5, Søren Rysgaard1, Niels Peter Revsbech2 1National Environmental Research Institute, Department of Marine Ecology, Vejlsøvej 25, 8600 Silkeborg, Denmark 2University of Aarhus, Institute of Biological Sciences, Department of Microbial Ecology, Ny Munkegade Building 540, 8000 Århus C, Denmark 3Delft University of Technology, Department of Biotechnology, Delft, The Netherlands 4KU Nijmegen, Department of Microbiology, Nijmegen, The Netherlands 5Depto. Ecologia, CCS, Ilha do Fundao, Cidade Universitaria, Universidade Federal do Rio de Janeiro, Rio de Janeiro, 21951-590, Brasil ABSTRACT: The occurrence and significance of the anammox (anaerobic ammonium oxidation) process relative to denitrification was studied in photosynthetically active sediment from 2 shallow-water estuaries: Randers Fjord and Norsminde Fjord, Denmark. Anammox accounted for 5 to 24% of N2 pro- duction in Randers Fjord sediment, whereas no indication was seen of the process in sediment from Nors- minde Fjord. It is suggested that the presence of anammox in Randers Fjord and its absence from Nors- – – – minde Fjord is associated with differences in the availability of NO3 + NO2 (NOx ) in the suboxic zone – – of the sediment. In Randers Fjord, NOx is present in the water column throughout the year and NOx – porewater profiles showed that NOx penetrates into the suboxic zone of the sediment. In Norsminde – Fjord, NOx is absent from the water column during the summer months and, via assimilation, benthic mi- – croalgae may prevent penetration of NOx into the suboxic zone of the sediment. Volume-specific anam- mox rates in Randers Fjord were comparable with rates measured previously in Skagerrak sediment by other investigators, but denitrification rates were 10 to 15 times higher. Thus, anammox contributes less to N2 production in Randers Fjord than in Skagerrak sediment. We propose that the lower contribution of anammox in Randers Fjord is linked to the higher availability of easily accessible carbon, which sup- ports a higher population of denitrifying bacteria. Amplification of DNA extracted from the sediment sam- ples from Randers Fjord using planctomycete-specific primers yielded 16S rRNA gene sequences closely related to candidatus Scalindua sorokinii found in the Black Sea by other investigators. The present study thus confirms the link between the presence of bacteria affiliated with candidatus S. sorokinii and the anammox reaction in marine environments. Anammox rates in sediment with intact chemical gradients were estimated using both 15N and microsensor techniques. Anammox rates estimated with microsensors were less than 22% of the rates measured with isotopes. It is suggested that this discrepancy was due to 15 the presence of fauna, because the applied N technique captures total N2 production while the micro- sensor technique only captures diffusion-controlled N2 production at the sediment surface. This hypo- thesis was verified by consistent agreement between the methods when applied to defaunated sediments. KEY WORDS: Anammox · Denitrification · Planctomycetes · Scalindula Resale or republication not permitted without written consent of the publisher INTRODUCTION removal of nitrogen from the sea (Devol 1991). Until recently, it was believed that denitrification was based – – The biologically mediated reduction of NO3 + solely on the reduction of NOx to N2 in an oxygen-free – – NO2 (NOx ) to N2 through denitrification is generally environment by facultatively aerobic bacteria with an considered to be the major process responsible for organotrophic metabolism (Zumft 1992). Within this *Email: [email protected] © Inter-Research 2004 · www.int-res.com 294 Aquat Microb Ecol 36: 293–304, 2004 – model, the major NOx source for denitrification is nitri- occurrence of anammox bacteria of the phylum Planc- + – fication, i.e. the bacterial oxidation of NH4 or NO2 tomycetes. The few published data addressing the with O2. Nitrification and denitrification are associated occurrence and significance of this newly discovered with the sediment/water interface in marine sedi- process in marine environments originate mainly from ments. Nitrification takes place in the upper oxic zone studies of deep-water, offshore sediments and anoxic of the sediment and denitrification in the suboxic zone water columns (see Dalsgaard & Thamdrup 2002, just below the oxic/suboxic interface (Jensen et al. Thamdrup & Dalsgaard 2002, Dalsgaard et al. 2003, 1993, 1994). According to the classical concept, cou- Kuypers et al. 2003). These studies suggested that the pled nitrification–denitrification is facilitated by the anammox reaction may account for 30 to 70% of – – transport of NOx from the oxic NOx production zones oceanic N2 production (Devol 2003), which poses a – to the suboxic NOx consumption zones in the sedi- great challenge to our view on the control of marine N2 – ment. In bioturbated sediments, the transport of NOx production. Only very recently has anammox activity from oxic to suboxic zones may be further enhanced by been located in estuarine sediment from the Thames fauna-mediated processes such as biodiffusion and estuary, UK (Trimmer et al. 2003), where it accounted irrigation (Aller 1982, Aller & Aller 1998, Kristensen for <10% of benthic N2 production. 2000 and references therein). This enhanced transport The present study addresses the occurrence and sig- results in elevated production of N2 (e.g. Pelegri et al. nificance of the anammox process relative to denitrifi- 1994, Svensson et al. 2001, Newell et al. 2002). cation in photosynthetically active sediments from 2 The classical view has recently been challenged by shallow-water estuaries: Randers Fjord and Norsminde the discovery of alternative pathways of combined Fjord, Denmark. We identified bacteria responsible for nitrogen transformations. These alternative pathways the process using anammox-specific FISH (fluores- + – include the anaerobic oxidation of NH4 to NO3 or N2 cence in situ hybridization) probes, 16S rRNA gene- with manganese oxides (Luther et al. 1997, Hulth et al. targeted PCR amplification with anammox-specific + 1999) and the anaerobic oxidation of NH4 to N2 with primers, and subsequent sequencing and phylogenetic – NO2 (Mulder et al. 1995). While direct experimental analysis (Schmid et al. 2000). We furthermore obtained + evidence for anaerobic NH4 oxidation to N2 with man- quantitative data on the denitrification and anammox ganese oxides is still lacking (Thamdrup & Dalsgaard process rates. In order to compare the results of the + 2000), it is now well documented that NH4 can be oxi- present study with data from previous studies of the – dized anaerobically to N2 with NO2 both in marine anammox process in marine sediments, we assessed sediments and in open waters (Dalsgaard & Thamdrup anammox and denitrification activity in sediment slur- 2002, Thamdrup & Dalsgaard 2002, Dalsgaard et ries according to Thamdrup & Dalsgaard (2002). This al. 2003, Kuypers et al. 2003, Trimmer et al. 2003). technique estimates the volume-specific anammox and This biologically mediated process is called anammox denitrification rates. To assess process rates in sedi- (anaerobic ammonium oxidation) (Strous et al. 1999). ments with intact chemical gradients, we combined Strictly viewed, anammox is equivalent to denitrifica- techniques that estimate benthic N2 production in in- tion since denitrification is defined as the conversion of tact sediment cores (Nielsen 1992, Risgaard-Petersen – 15 NO2 to gaseous N (Payne 1981). However, existing et al. 2003) with the N technique of Thamdrup & literature addressing anammox in natural environ- Dalsgaard (2002), which also estimates the contribu- ments (Dalsgaard & Thamdrup 2002, Thamdrup & tion of anammox to total N2 production. In addition, Dalsgaard 2002, Trimmer et al. 2003) uses the term de- N2 production was estimated from porewater profiles – – nitrification for the purely NOx -based N2 production of NOx , to address the diffusion-controlled activity – (E-donor + 2NOx → N2) and the term anammox for the directly linked to the sediment surface. Microsensor + – – production of N2 from NH4 and NO2 . For the sake of profiles of O2 and NOx were furthermore used to consistency, we choose to follow this nomenclature. obtain a detailed picture of the distribution of oxic and – Little is known about the biogeography of the anam- suboxic zones as well as zones of NOx production and – mox process, its microbiology, and its importance as consumption. As O2 exposure and NOx availability a source of N2 production relative to denitrification. would be key factors in determining the distribution of According to current knowledge, the anammox pro- anammox bacteria in the sediment, these detailed ob- cess is carried out by autotrophic, obligately anaerobic servations could explain some of the trends observed bacteria of the