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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 8, issue 2
Biogeosciences, 8, 253–265, 2011
https://doi.org/10.5194/bg-8-253-2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: Interactions between planktonic organisms and the biogeochemical...

Biogeosciences, 8, 253–265, 2011
https://doi.org/10.5194/bg-8-253-2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 07 Feb 2011

Research article | 07 Feb 2011

Flow cytometric assessment of specific leucine incorporation in the open Mediterranean

A. Talarmin1,2,3,4, F. Van Wambeke1,2, P. Catala3,4, C. Courties3,5, and P. Lebaron3,4 A. Talarmin et al.
  • 1Université de la Méditerranée, Centre d'Océanologie de Marseille, Case 901, Campus de Luminy, 13288 Marseille, France
  • 2CNRS/INSU, UMR 6117, LMGEM, Case 901, Campus de Luminy, 13288 Marseille, France
  • 3UPMC Univ Paris 06, Laboratoire ARAGO – Observatoire Océanologique, 66651 Banyuls/mer, France
  • 4CNRS, UMR 7621, LOMIC, Observatoire Océanologique, 66651 Banyuls/mer, France
  • 5CNRS, UMS 2348, Observatoire Océanologique, 66651, Banyuls/mer, France

Abstract. The surface of the Mediterranean Sea is a low-phosphate-low-chlorophyll marine area where marine heterotrophic prokaryotes significantly contribute to the biogeochemical cycles of all biogenic elements such as carbon, notably through the mineralization of dissolved organic compounds. Cell-specific leucine incorporation rates were determined in early summer in the open stratified Mediterranean Sea. The bulk leucine incorporation rate was on average 5 ± 4 pmol leu l−1 h−1 (n=30). Cell-specific 3H-leucine incorporation rates were assayed using flow cytometry coupled to cell sorting. Heterotrophic prokaryotes (Hprok) were divided into cytometric groups according to their side scatter and green fluorescence properties: high nucleic acid containing cells (HNA) with high scatter (HNA-hs) and low scatter (HNA-ls) and low nucleic acid containing cells (LNA). Cell-specific leucine incorporation rates of these cytometric groups ranged from 2 to 54, 0.9 to 11, and 1 to 12 × 10-21 mol cell−1 h−1, respectively. LNA cells represented 45 to 63% of the Hprok abundance, and significantly contributed to the bulk leucine incorporation rates, from 12 to 43%. HNA/LNA ratios of cell-specific leucine incorporation were on average 2.0 ± 0.7 (n=30). In surface layers (from 0 m down to the deep chlorophyll depth, DCM), cell-specific rates of HNA-hs were elevated (7 and 13 times greater than LNA and HNA-ls, respectively). Nevertheless, on average HNA-hs (26%) and LNA (27%) equally contributed to the bulk leucine incorporation in these layers. Prochlorococcus cells were easily sorted near the DCM and displayed cell-specific leucine incorporation rates ranging from 3 to 55 × 10-21 mol leu cell−1 h−1, i.e. as high as HNA-hs'. These sorted groups could therefore be defined as key-players in the process of leucine incorporation into proteins. The mixotrophic features of certain photosynthetic prokaryotes and the high contribution of LNA cells to leucine incorporation within the microbial communities of the Mediterranean could be reinforced.

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