This 2004 GRC will be the first one of a new series dedicated to Marine Microbes. Microbes (i.e. virus, Bacteria, Archaea, Eukaryota; autotrophic and heterotrophic) lie at the heart of the functioning of all marine ecosystems, from the surface euphotic zone to deep hydrothermal vents. Marine microbes drive the natural biogeochemical cycles and, in turn, are affected by anthropogenic influences. Thus, these microbes are directly relevant to many societal concerns of the global environment: biodiversity, climate change, harvestable resources and others. The last two decades have seen an explosion of studies devoted to these organisms. The use of molecular tools has been critical in this respect. It is timely to initiate this series with a conference on picophytoplankton because this field appears to be poised at a turning point.

Picophytoplankton, discovered in the late 1970s, are unicellular photosynthetic organisms less than 2 to 3 microns in size. These marine microbes dominate biomass and production in large regions of the ocean, thus playing a key role in global elemental cycles such as that of carbon. Nearly 20 years after the NATO Advanced Study Institute on picoplankton organized by T. Platt and W.K.W. Li, the time has arrived for a new meeting to summarize the current state of knowledge. To date, a very large amount of data has been gathered on picophytoplankton. Information on ecological distributions and taxonomic diversity have come from novel approaches such as flow cytometry and molecular biology. More strikingly, the recent development of genomics of picoplankton species such as Prochlorococcus, Synechococcus and Ostreococcus provide new and fundamental insight. This meeting will first review recent advances in the taxonomy of picophytoplankton, especially the discovery of many novel eukaryotic groups both from culture and molecular-based field studies. In particular, we will cover extensively the new tools of molecular biology. Then, we will examine the physiology and ecology of picophytoplankton and revisit its role in the microbial food web. Finally we will dwell on the very exciting developments in picophytoplankton genomics and how the new knowledge will impact on our understanding of marine ecosystems.