Das Projekt "Molecular ecology of the photosynthetic procaryote prochlorococcus, a key organism of oceanic ecosystems" wird vom Umweltbundesamt gefördert und von Universität Berlin (Humboldt-Univ.), Institut für Biologie, Arbeitsgruppe Molekulare Biologie und Biochemie, Genetik durchgeführt. General Information: The application of molecular biology to oceanography is still little developped, especially in Europe. However, it is a very promising field for marine biologists, who have become able to address key ecological questions with a level of resolution never attained by previous methods. It is now possible to directly use molecular probes on field samples either to assess the extent of genetic diversity in genetically related marine organisms or to probe their nutrient status. The present project is centered on an important and recently discovered genus of marine photosynthetic microorganism: Prochlorococcus. This prokaryote proliferates in oligotrophic areas, including the Mediterranean and Red Seas, is the tiniest and numerically the most abundant photosynthetic organism on Earth and accounts for a large part (up to 50 per cent) of the photosynthetic biomass and primary production in these areas. Moreover, Prochlorococcus has the advantages of being easily discriminated and counted by flow cytometry and of possessing a unique pigment signature (divinyl-chlorophylls a and b). In addition, natural isolates from a variety of sites and depths are available under laboratory conditions. Prochlorococcus therefore constitutes an outstanding biological model for ecological studies. In the framework of the Promolec project, we will: 1) study the intrageneric diversity of Prochlorococcus in the laboratory and in the field, with an effort to correlate the phenotypical and genotypical characters, 2) characterize the genes encoding cellular components responsible for ecologically significant functions (photosynthesis, growth, responses to nitrogen and phosphorus limitation) and study their regulation, 3) develop a set of molecular probes and screen these functions in natural Prochlorococcus populations. Because of the remarkable ecological importance of Prochlorococcus, which can be considered as a biological tracer of oligotrophy, this project is expected: 1) to improve the knowledge of the actual status of oligotrophic areas 2) to provide means to monitor biological changes that may occur in response to variations in short or long-term hydrological conditions (including the global man-induced increase in carbon dioxyde in the atmosphere) 3) to help identify key factors controlling the genetic diversity in picophytoplankton. Promolec fits well with the priority theme N- 1 defined in the second call for proposal to MAST-III. Prime Contractor: Centre National de la Recherche Scientifique, UMR 1931, Station Biologique de Roscoff SBR; Roscoff; France.