The role of iron (Fe) in controlling in situ distributions and activities of marine synechococcus

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The unicellular cyanobacterium Synechococcus is one of the most abundant primary producers in the marine environment. It is also extremely widespread; Synechococcus has been found in open ocean, coastal and even polar environments. Unlike its close relative, Prochlorococcus, Synechococcus has the ability to use NO3 and has been shown to respond in the field to NO3 inputs, suggesting that this organism may play a key role in global carbon cycling and especially new production. To date, 16 potential clades have been identified, and it is thought that this high diversity allows for the radiation of Synechococcus into many different environmental conditions. However, despite the ubiquity and abundance of Synechococcus, there are few studies characterizing the physiology and niche adaptations of each clade. Iron (Fe) shows great potential as a defining factor for niche adaptations, as its concentration varies over the geographic range of Synechococcus, as well as annually at specific locations, and has been shown to limit primary production in both open ocean and coastal settings. In addition, culture work indicates that Synechococcus strains have different abilities to grow on low concentrations of Fe. A comparison of the available genomes of marine Synechococcus shows great diversity in the presence or absence of known genes related to Fe stress, suggesting that Fe could have played a key role in the diversification and niche adaptation of Synechococcus. This project will study the effects of Fe on growth and carbon fixation in 11 different clades of Synechococcus (using at least 2 strains from each clade whenever possible) and the role of Fe limitation in determining the distribution of Synechococcus clades on temporal and spatial scales. This project will produce a comprehensive and systematic data set on the impact of Fe-specific niche differentiation in Synechococcus, offer new insight into the factors that control clade distribution, and provide understanding of the biogeochemical consequences of Synechococcus diversity. Broader Impacts In addition to defining the role and impact of Fe limitation on marine Synechococcus, both in the lab and in the field, this project will develop quantitative PCR-based Fe stress diagnostics that will be available to the community. These data will also allow for improved parameterization of models in which phytoplankton groups are differentiated, therefore improving the ability to predict the dynamics of biogeochemical cycles. The results of this research will be widely disseminated at national conferences. Furthermore, this project will completely fund and provide valuable research experience and career development for post-doctoral fellow Dr. Jill A Sohm, as well as two undergraduates participating in summer research.