Examining nitrate reduction by phytoplankton with an inmunoassay.

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Use of Fluorescein Diacetate (FDA) as a Single-Cell Probe of metabolic Activity in Dinoflagellate Cultures.

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Influence of upwelling relaxation on dinoflagellate and Shellfish Toxicity in Ría de Vigo, Spain

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Flow cytometric identification and enumeration of photosynthetic sulfur bacteria and potential for ecophysiological studies at the single-cell level

17 páginas, 9 figuras, 2 tablas.We show the potential of flow cytometry as a fast tool for population identification and enumeration of photosynthetic sulfur bacteria. Purple (PSB) and green sulfur bacteria (GSB) oxidize hydrogen sulfide to elemental sulfur that can act as storage compound to be further oxidized to sulfate generating the reducing power required for growth. Both groups have different elemental sulfur allocation strategies: whereas PSB store elemental sulfur as intracellular inclusions, GSB allocate sulfur globules externally. We used well-characterized laboratory strains and complex natural photosynthetic populations developing in a sharply stratified meromictic lake to show that PSB and GSB could be detected, differentiated and enumerated in unstained samples using a blue laser-based flow cytometer. Variations in cell-specific pigment content and the dynamics of sulfur accumulation, both intra- and extracellularly, were also detected in flow cytometric plots as sulfur accumulation changed the light scatter characteristics of the cells. These data were used to show the potential for studies on the metabolic status and the rate of activity at the single-cell level. Flow cytometric identification and enumeration resulted in faster and more precise analyses than previous approaches, and may open the door to more complex ecophysiological experiments with photosynthetic sulfur bacteria in mixed cultures and natural environments.This work was financed by the coordinated project VIARC Grant No. REN2003-08333 to E.O.C. and C.M.B. and MicroDiff and Modivus Grants REN2001-2120/MAR and CTM2005-04795/MAR to J.M.G. from the Spanish Ministerio de Educación y Ciencia (MEC). We thank J. Mas for support and lab facilities at the Department of Genetics and Microbiology, Autonomous University of Barcelona. E.O.C. benefits from the Program Ramon y Cajal of the Spanish MEC and FEDER.Peer reviewe