Members of two closely related cyanobacterial groups, Synechococcus and Prochlorococcus, are ubiquitous and abundant in the world's oceans, and represent a significant fraction of the overall primary producer biomass and activity in many marine environments. This study has as its major goal the development of non incubation approaches for measuring in situ growth rates of natural Synechococcus populations. Ultimately, the information from such studies will enhance our understanding of the mechanisms by which oceanic primary producer communities are structured, and help us predict the effects of environmental perturbations on those communities. The development of non incubation growth rate measurements requires a thorough knowledge of the physiology of cell growth and division in the organisms of interest. A large part of this project involves gaining such knowledge for marine Synechococcus species. Representative isolates will be cultured under defined laboratory conditions. These conditions will be varied in order to achieve a range of growth rates controlled by a variety of environmental factors. For each strain growing under each set of conditions, average cellular characteristics (and the population distribution of those characteristics) will be measured flow cytometrically. In this way, the relationships between the cell cycle (as reflected in DNA distributions), biochemical composition, and growth rate will be established. These data will be used to develop cell cycle or biochemical indexes that are robustly related to Synechococcus growth rate. Finally, these indexes will be compared with more traditional methods for measuring growth rates in natural samples from the north Atlantic Ocean and Sargasso Sea.
