Characterization of organic iron and cobalt ligands in the subtropical North Pacific

Abstract

Trace metals are essential to the growth of marine organisms, but they exist in very low concentrations in the ocean, and are mostly complexed to diverse suites of organic ligands. While these metal-binding ligands directly impact metal speciation, reactivity, and bioavailability, the distributions and cycling of these ligands still remains relatively unclear. Recently, direct molecular characterization of individual ligands became possible through developments in liquid chromatography and mass spectrometry tools. My dissertation uses liquid-chromatography mass-spectrometry (LC-MS) techniques to characterize metal-binding organic ligands in seawater in order to understand how these ligands affect the biogeochemical cycles of trace metals and impact microbial community structure. I quantified and characterized siderophores, a class of strong iron-binding ligands, in the subtropical North Pacific. Combining of this data with metagenomes and metatranscriptomes analyses provided additional insight on how different siderophores are being actively produced and consumed by distinct microbial groups. I also explored the identity of cobalt binding ligands, whose sources, sinks and chemical structures are largely unknown. Despite the widespread assumption that cobalt ligands are related to cyanocobalamin and its degradation products, it may be possible that there are additional unknown ligands that can bind cobalt. Overall, this dissertation expands the availability of organic iron- and cobalt-binding ligand data in the marine environment, and presents examples of the interplay between the distribution and speciation of trace metals and marine microbial communities.