The Influence of Iron on the Cellular Quota of Prochlorococcus

Factors that control the distribution of marine phytoplankton are critical to our understanding of the primary productivity and global carbon cycling. In addition, the pigmentation of phytoplankton and the exudates of phytoplankton (colored dissolved organic matter) are two of the major factors influencing ocean optical properties. The cyanobacteria, including Prochlorocococcus marinus, are among the most abundant phytoplankton in the oceans, and hence contribute to both carbon cycling and ocean optical properties. Through this ONR-YIP grant, our laboratory has been studying an important component relating to growth of Prochlorococcus: the cellular iron quota. Because Prochlorococcus is relatively difficult to grow and cultures free of bacterial contaminants were only recently produced, studies of the elemental composition of this key phytoplankter have not been possible until very recently. Yet, global ecosystem modelers require iron quotas for all key phytoplankton groups in order to improve our predictive ability of primary productivity and the seawater optical properties throughout the oceans.