AME 51:45-53 (2008)  -  DOI:

High abundance of diazotrophic picocyanobacteria (<3 µm) in a Southwest Pacific coral lagoon

Isabelle C. Biegala1,*, Patrick Raimbault2

1Institut de Recherche pour le Développement, UR103 CAMELIA, Centre d’Océanologie de Marseille, rue de la Batterie des Lions, Marseille 13007, France
2Laboratoire d’Océanologie et de Biogéochimie, UMR6535, Centre d’Océanologie de Marseille, Campus de Luminy case 901, Cedex 9, Marseille 13288, France

ABSTRACT: In the present study we detected unicellular diazotrophic cyanobacteria along a nutrient gradient in New Caledonia’s coral lagoon (24000 km2) using whole-cell hybridization of specific Nitro821 probes (TSA-FISH, Tyramide Signal Amplification of Fluorescent In Situ Hybridization). The specificity of this probe was confirmed on cultures and in the natural environment. Surprisingly, the community of Nitro821-targeted cells was numerically dominated by picocyanobacteria (97%, 1 to 1.5 µm). These organisms were either free living (63%), recovered with the 0.2 to 3 µm size fraction or associated (37%) to particles or planktonic dinoflagellates from larger size fractions (3 to 10 µm and >10 µm). Diazotrophic picocyanobacterial abundance ranged from 3 to 140 cells ml–1 along the nutrient gradient and was highest at the oligotrophic lagoonal station. These cells may contribute to N2 fixation from the <10 µm size fraction (4.4 to 8 nmol N–1 24 h–1), which was 4 times higher than the >10 µm size fraction (0 to 1.9 nmol N–1 24 h–1). In addition, in the middle of the lagoon daylight 15N2 fixation could explain 78% of 15N2 fixation over 24 h. The results presented in the present study reveal for the first time a significant concentration of photosynthetic diazotrophs within the marine picoplankton community.

KEY WORDS: Diazotrophs · Cyanobacteria · Picoplankton · FISH · Pacific · Coral lagoon · Symbiosis

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Cite this article as: Biegala IC, Raimbault P (2008) High abundance of diazotrophic picocyanobacteria (<3 µm) in a Southwest Pacific coral lagoon. Aquat Microb Ecol 51:45-53.

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