Molecular determination of marine iron ligands by mass spectrometry
Citable URI
https://hdl.handle.net/1912/7837Location
39.43°N, 124.54°WDOI
10.1575/1912/7837Abstract
Marine microbes produce a wide variety of metal binding organic ligands that regulate the
solubility and availability of biologically important metals such as iron, copper, cobalt, and zinc.
In marine environments where the availability of iron limits microbial growth and carbon
fixation rates, the ability to access organically bound iron confers a competitive advantage. Thus,
the compounds that microbes produced to acquire iron play an important role in biogeochemical
carbon and metal cycling. However, the source, abundance, and identity of these compounds are
poorly understood. To investigate these processes, sensitive methodologies were developed to
gain a compound-specific window into marine iron speciation by combining trace metal clean
sample collection and chromatography with inductively coupled plasma mass spectrometry (LCICPMS)
and electrospray ionization mass spectrometry (LC-ESIMS). Coupled with isotope
pattern assisted search algorithms, these tools provide a means to quantify and isolate specific
iron binding ligands from seawater and marine cultures, identify them based on their mass and
fragmentation spectra, and investigate their metal binding kinetics.
Using these techniques, we investigated the distribution and diversity of marine iron binding
ligands. In cultures, LC-ICPMS-ESIMS was used to identify new members of siderophore
classes produced by marine cyanobacteria and heterotrophic bacteria, including synechobactins
and marinobactins. Applications to natural seawater samples from the Pacific Ocean revealed a
wide diversity of both known and novel metal compounds that are linked to specific nutrient
regimes. Ferrioxamines B, E, and G were identified in productive coastal waters near California
and Peru, in oligotrophic waters of the North and South Pacific Gyre, and in association with
zooplankton grazers. Siderophore concentrations were up to five-fold higher in iron-deficient
offshore waters (9pM) and were dominated by amphibactins, amphiphilic siderophores that
partition into cell membranes. Furthermore, synechobactins were detected within nepheloid
layers along the continental shelf. These siderophores reflect adaptations that impact dissolved
iron bioavailability and thus have important consequences for marine ecosystem community
structures and primary productivity. The ability to map and characterize these compounds has
opened new opportunities to better understand mechanisms that link metals with the microbes
that use them.
Description
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2016
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Suggested Citation
Thesis: Boiteau, Rene M., "Molecular determination of marine iron ligands by mass spectrometry", 2016-02, DOI:10.1575/1912/7837, https://hdl.handle.net/1912/7837Related items
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