Organic Copper Speciation in the North Pacific

Organic ligands mediate the biogeochemical cycling of many bioessential trace metals, including copper. Copper is both an essential micronutrient (as a cofactor for key enzymes such as nitrite reductase, nitrous oxide reductase, and ammonium monooxygenase) and a toxin. Even at picomolar concentrations, free copper can inhibit the growth of cyanobacteria such as Prochlorococcusand Synechococcus). It has been observed that microbes produce strong copper-binding ligands in response to copper toxicity as well as in copper-limiting conditions, however the identities of these organic compounds have not been characterized. Using high performance liquid chromatography coupled to ICP and ESI mass spectrometry, we are able to separate and quantify copper ligands as well as attain molecular level information including molecular weight, elemental composition, and the presence of specific functional groups. We routinely observe copper ligand complexes in both seawater and spent media from laboratory cultures of marine cyanobacteria. In order to explore a potential biological sources of copper ligands, we examined the copper ligands produced by different strains of Synechococcusand Prochlorococcusand compared them to copper ligands found in seawater samples from the North Pacific. Preliminary data show suites of copper ligands present in both seawater and culture samples, with putative molecular formulae indicating the presence of both Cu(I) and Cu(II) ligand complexes.