9417071 Campbell The recently discovered photosynthetic prokaryotes Prochlorococcus spp., which contain a unique set of pigment including divinyl chlorophyll a and b, have been shown to be an important component of the phytoplankton community contributing 25 to 60% of total chlorophyll biomass. In the subtropical central Pacific Ocean, Prochlorococcus dominate in the upper 100 m of the water column in chlorophyll and carbon biomass. The primary goal of this research is this research is to examine the factors which limit the growth and distribution of Prochlorococcus. A primary objective is to investigate the effects of light and nitrogen-source on the growth of different Prochlorococcus strains in culture and in the field. Specifically the research will conduct the following experiments on laboratory cultures of Prochlorococcus: 1) compare the effects of irradiance and nitrogen source on photosynthetic parameters (P vs. I and N vs. I), nitrogen uptake rates and growth rates; 2) determine nitrogen uptake rates of varying Prochlorococcus populations in the central Pacific; and 3) assess the ability of NH4 to inhibit NO3 and urea uptake in Prochlorococcus. In addition to the laboratory experiments, four quarterly cruises will be conducted to station ALOHA in the North Pacific where field populations of Prochlorococcus will be compared with the distribution of other phytoplankton species with depth and nutrient profiles. Further, field populations of Prochlorococcus will be assayed for growth rates, the effects of light intensity on growth rate, and nutrients addition experiments. Finally, monoclonal antibody probes will be used to provide a means of certain identification and enumeration of distinct Prochlorococcus populations.
