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Applied and Environmental Microbiology, May 2009, p. 3171-3179, Vol. 75, No. 10
0099-2240/09/$08.00+0 doi:10.1128/AEM.02511-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
Changes in Benthic Denitrification, Nitrate Ammonification, and Anammox Process Rates and Nitrate and Nitrite Reductase Gene Abundances along an Estuarine Nutrient Gradient (the Colne Estuary, United Kingdom)
,
Liang F. Dong,1,
Cindy J. Smith,1,2,
Sokratis Papaspyrou,1,
Andrew Stott,3
A. Mark Osborn,1,2 and
David B. Nedwell1*
Department of Biological Sciences, University of Essex, Colchester CO4 3SQ, United Kingdom,1 Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield S10 2TN, United Kingdom,2 NERC Life Sciences Mass Spectrometer Facility, Centre for Ecology & Hydrology, Lancaster Environment Centre, Lancaster LA1 4AP, United Kingdom3
Received 3 November 2008/ Accepted 11 March 2009
Estuarine sediments are the location for significant bacterial removal of anthropogenically derived inorganic nitrogen, in particular nitrate, from the aquatic environment. In this study, rates of benthic denitrification (DN), dissimilatory nitrate reduction to ammonium (DNRA), and anammox (AN) at three sites along a nitrate concentration gradient in the Colne estuary, United Kingdom, were determined, and the numbers of functional genes (narG, napA, nirS, and nrfA) and corresponding transcripts encoding enzymes mediating nitrate reduction were determined by reverse transcription-quantitative PCR. In situ rates of DN and DNRA decreased toward the estuary mouth, with the findings from slurry experiments suggesting that the potential for DNRA increased while the DN potential decreased as nitrate concentrations declined. AN was detected only at the estuary head, accounting for 
30% of N2 formation, with 16S rRNA genes from anammox-related bacteria also detected only at this site. Numbers of narG genes declined along the estuary, while napA gene numbers were stable, suggesting that NAP-mediated nitrate reduction remained important at low nitrate concentrations. nirS gene numbers (as indicators of DN) also decreased along the estuary, whereas nrfA (an indicator for DNRA) was detected only at the two uppermost sites. Similarly, nitrate and nitrite reductase gene transcripts were detected only at the top two sites. A regression analysis of log(n + 1) process rate data and log(n + 1) mean gene abundances showed significant relationships between DN and nirS and between DNRA and nrfA. Although these log-log relationships indicate an underlying relationship between the genetic potential for nitrate reduction and the corresponding process activity, fine-scale environmentally induced changes in rates of nitrate reduction are likely to be controlled at cellular and protein levels.
* Corresponding author. Mailing address: Department of Biological Sciences, University of Essex, Colchester CO4 3SQ, United Kingdom. Phone: 44 1206 872211. Fax: 44 1206 873416. E-mail: nedwd{at}essex.ac.uk
Published ahead of print on 20 March 2009.
Supplemental material for this article may be found at http://aem.asm.org/.
L.F.D. and C.J.S. contributed equally to this research.
Present address: Instituto de Ciencias Marinas de Andalucia—CSIC, Pol. Rio San Pedro s/n, 11510 Puerto Real (Cadiz), Spain.
Applied and Environmental Microbiology, May 2009, p. 3171-3179, Vol. 75, No. 10
0099-2240/09/$08.00+0 doi:10.1128/AEM.02511-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
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