Collaborative Research: The Effect of Iron Bioavailability on Synechococcus diversity from a HNLC regime to the Costa Rica upwelling dome

University Of Washington, Seattle WA

Investigators

Abstract

On Earth, photosynthetic fixation of CO2 from the oceans accounts for approximately half of total global primary production. In the central oceanic gyres the most numerous photosynthetic organisms are the picoplankton, Synechococcus and Prochlorococcus. Recently it has been shown that these populations consist of numerous closely related but genetically distinct ecotypes. Of the more than ten clades of Synechococcus identified to date, only a few have been associated with a phenotype, while the factors differentiating the remaining clades are not yet understood. These investigators hypothesize that the bioavailability of the trace metal iron (Fe) is an important factor driving the differentiation in this genus. Understanding if and when Fe is limiting Synechococcus productivity and how this limitation modulates Synechococcus community structure will increase our understanding of how this important trace element impacts oceanic biogeochemical cycles and the diversity of the organisms mediating some of these cycles. This project: 1) is developing a whole cell labeling Fe stress assay for marine Synechococcus,, 2) is probing the Synechococcus community for Fe stress using whole cell labeling coupled with flow cytometry to sort the stressed cells from the replete cells on a transect in the Eastern Pacific through oligotrophic and high nutrient low chlorophyll (HNLC) regimes to the Costa Rica upwelling dome, 3) is examining the genetic diversity of Synechococcus along the transect using community fingerprinting methods and determining the genetic clade of the cells that are Fe-stressed or Fe replete and 4) isolating new strains of marine Synechococcus from oligotrophic, HNLC, and Costa Rica upwelling regimes and characterize their phylogeny and Fe physiology. This project is taking advantage of existing cruise opportunities to the Costa Rica upwelling dome (CRD), where remarkably high concentrations (106/ml) of Synechococcus have been reported. Available ancillary data on both trace metal concentrations and speciation is providing an unprecedented opportunity to examine how the interplay of multiple trace metals (Fe, Co, Cu, Zn, Cd) is contributing to maintaining genetic diversity in these picoplankters. This project is training two graduate students and several undergraduate research fellows. Funds are allowing some of these students to attend national meetings. Priority is being given to students from under-represented groups at small colleges.