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Applied and Environmental Microbiology, November 2009, p. 6662-6670, Vol. 75, No. 21
0099-2240/09/$08.00+0     doi:10.1128/AEM.01002-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Use of Inorganic and Organic Nitrogen by Synechococcus spp. and Diatoms on the West Florida Shelf as Measured Using Stable Isotope Probing{triangledown} ,{dagger}

Boris Wawrik,1* Amy V. Callaghan,1 and Deborah A. Bronk2

Department of Botany and Microbiology, University of Oklahoma, Norman, Oklahoma,1 Virginia Institute of Marine Science, The College of William and Mary, Williamsburg, Virginia2

Received 1 May 2009/ Accepted 28 August 2009

The marine nitrogen (N) cycle is a complex network of biological transformations in different N pools. The linkages among these different reservoirs are often poorly understood. Traditional methods for measuring N uptake rely on bulk community properties and cannot provide taxonomic information. 15N-based stable isotope probing (SIP), however, is a technique that allows detection of uptake of individual N sources by specific microorganisms. In this study we used 15N SIP methodology to assess the use of different nitrogen substrates by Synechococcus spp. and diatoms on the west Florida shelf. Seawater was incubated in the presence of 15N-labeled ammonium, nitrate, urea, glutamic acid, and a mixture of 16 amino acids. DNA was extracted and fractionated using CsCl density gradient centrifugation. Quantitative PCR was used to quantify the amounts of Synechococcus and diatom DNA as a function of density, and 15N tracer techniques were used to measure rates of N uptake by the microbial community. The ammonium, nitrate, urea, and dissolved primary amine uptake rates were 0.077, 0.065, 0.013, and 0.055 µmol N liter–1 h–1, respectively. SIP data indicated that diatoms and Synechococcus spp. actively incorporated N from [15N]nitrate, [15N]ammonium, and [15N]urea. Synechococcus also incorporated nitrogen from [15N]glutamate and 15N-amino acids, but no evidence indicating uptake of labeled amino acids by diatoms was detected. These data suggest that N flow in communities containing Synechococcus spp. and diatoms has more plasticity than the new-versus-recycled production paradigm suggests and that these phytoplankters should not be viewed strictly as recycled and new producers, respectively.

* Corresponding author. Mailing address: University of Oklahoma, George Lynn Cross Hall, 770 Van Vleet Oval, Norman, OK 73019-4110. Phone: (405) 325-4321. Fax: (405) 325-7619. E-mail: bwawrik{at}ou.edu

{triangledown} Published ahead of print on 4 September 2009.

{dagger} VIMS contribution 3042 from the Virginia Institute of Marine Science, The College of William and Mary.

Applied and Environmental Microbiology, November 2009, p. 6662-6670, Vol. 75, No. 21
0099-2240/09/$08.00+0     doi:10.1128/AEM.01002-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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