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Moffett, JW, Brand LE, Croot PL, Barbeau KA.  1997.  Cu Speciation and Cyanobacterial Distribution in Harbors Subject to Anthropogenic Cu Inputs. Limnology and Oceanography. 42:789-799.: American Society of Limnology and Oceanography   10.2307/2838883   AbstractWebsite

Cu speciation was studied in four harbors on the south coast of Cape Cod, Massachusetts, that are exposed to varying degress of Cu contamination from anthropogenic sources. Copper in waters outside the harbors was complexed by ∼ 10 nM of very strong chelators, twofold higher than ambient Cu concentrations. In Eel Pond (Woods Hole) and Falmouth Inner Harbor, total dissolved Cu concentrations were 7-10-fold higher. However, because the strong chelators were saturated in these two harbors, the free Cu increased by 1,000-fold, from $\thicksim 10^13 M$ to $\thicksim 10^-10 M$ . There was no evidence for any enhanced biological production of chelators in response to the elevated Cu concentrations. However, cell densities of cyanobacteria, which have been proposed as a source of strong Cu chelators in seawater, decline drastically in the high Cu harbors. These trends are consistent with culture studies showing that Synechococcus sp., the predominant cyanophyte in these waters, shows a dramatic decrease in growth rates above a free Cu2+ level of 10-11 M. In Great Pond and Waquoit Bay, which showed no significant Cu contamination or saturation of strong ligands, cyanobacterial cell densities showed little or no decrease. Results suggest that significant anthropogenic inputs of Cu may overwhelm processes occurring in seawater that lead Cu and strong chelator concentrations to approach comparable levels.

McQuaid, JB, Kustka AB, Obornik M, Horak A, McCrow JR, Karas BJ, Zheng H, Kindeberg T, Andersson AJ, Barbeau KA, Allen AE.  2018.  Carbonate-sensitive phytotransferrin controls high-affinity iron uptake in diatoms. Nature. 555:534-537.   10.1038/nature25982   AbstractWebsite

In vast areas of the ocean, the scarcity of iron controls the growth and productivity of phytoplankton(1,2). Although most dissolved iron in the marine environment is complexed with organic molecules(3), picomolar amounts of labile inorganic iron species (labile iron) are maintained within the euphotic zone(4) and serve as an important source of iron for eukaryotic phytoplankton and particularly for diatoms(5). Genome-enabled studies of labile iron utilization by diatoms have previously revealed novel iron responsive transcripts(6,7), including the ferric iron-concentrating protein ISIP2A(8), but the mechanism behind the acquisition of picomolar labile iron remains unknown. Here we show that ISIP2A is a phytotransferrin that independently and convergently evolved carbonate ion-coordinated ferric iron binding. Deletion of ISIP2A disrupts high-affinity iron uptake in the diatom Phaeodactylum tricornutum, and uptake is restored by complementation with human transferrin. ISIP2A is internalized by endocytosis, and manipulation of the seawater carbonic acid system reveals a second order dependence on the concentrations of labile iron and carbonate ions. In P. tricornutum, the synergistic interaction of labile iron and carbonate ions occurs at environmentally relevant concentrations, revealing that carbonate availability co-limits iron uptake. Phytotransferrin sequences have a broad taxonomic distribution(8) and are abundant in marine environmental genomic datasets(9,10), suggesting that acidification-driven declines in the concentration of seawater carbonate ions will have a negative effect on this globally important eukaryotic iron acquisition mechanism.