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Aquatic Microbial Ecology

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AME 53:271-280 (2008)  -  DOI:

Interactions between ammonium and urea uptake by five strains of Alexandrium catenella (Dinophyceae) in culture

Cécile Jauzein1,2, Sofia Loureiro3, Esther Garcés3, Yves Collos1,*

1Université Montpellier II, CC093, Laboratoire Ecosystèmes Lagunaires (UMR CNRS 5119), 34095 Montpellier Cedex 5, France
2Laboratoire Environnement Ressources/LR, Ifremer, BP 171, 34203 Sète, France
3Dept Biologia Marina, Institut de Ciències del MAR, CMIMA–CSIC, Pg. Marítim de la Barceloneta 37-49, 08003 Barcelona, Catalonia, Spain
*Corresponding author. Email:

ABSTRACT: Short-term experiments were carried out to investigate whether interactions between ammonium (NH4+) and urea uptake regulate the total nitrogen assimilation of the toxic dinoflagellate Alexandrium catenella. To test for strain variability, 5 strains of A. catenella from the NW Mediterranean were used: 3 strains from the Thau lagoon (southern France) and 2 strains from the Catalonia basin (Spain). For each strain, the uptake rate of 1 nutrient (NH4+ or urea) at a reference concentration (10 µgatN l–1) was measured as a function of the increasing concentration of the other nutrient (0 to 10 µgatN l–1). Simultaneous N uptake rates of the distinct nitrogen sources were obtained from 15N-NH4+ and 15N-urea incorporation measurements. A strong inhibition of urea uptake by NH4+ (maximum inhibition, Imax > 55%) was observed exclusively for the French strains. No influence of urea on the NH4+-uptake rate was noted for any strain. Estimation of total N uptake rates revealed that the N-urea uptake inhibition was not a competitive disadvantage for A. catenella cells considering that the reduced N-urea uptake was more than compensated for by NH4+ uptake. Furthermore, the computation of composite kinetic parameters from total N uptake data suggested that French strains were more competitive than the Spanish ones in an environment characterized by low NH4+ concentrations (≤5 µgatN l–1) and high urea concentrations (as 10 µgatN l–1). These N uptake characteristics may reflect particular metabolic adaptations by the strains to their respective environment.

KEY WORDS: Alexandrium catenella · Ammonium · Urea · Interactions · Strain variability

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Cite this article as: Jauzein C, Loureiro S, Garcés E, Collos Y (2008) Interactions between ammonium and urea uptake by five strains of Alexandrium catenella (Dinophyceae) in culture. Aquat Microb Ecol 53:271-280.

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