Investigating marine microbe/metal interactions with LC-ICPMS-ESIMS

Abstract:

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 these metals limits microbial growth and carbon fixation rates, the ability to access organically bound metal confers a competitive advantage. Thus, the speciation of metals and the compounds that microbes produced to acquire and detoxify them play an important role in biogeochemical carbon and metal cycling. However, the source, abundance, and identity of these compounds are poorly constrained.

To investigate these processes, we recently developed sensitive methodologies that offer a compound-specific window into marine metal speciation by combining trace metal clean sample collection and liquid chromatography with inductively coupled plasma mass spectrometry (LC-ICPMS) and electrospray ionization mass spectrometry (LC-ESIMS). LC-ICPMS is used to investigate the abundance and chemical diversity of metal-binding organics in the marine environment. We then use LC-ESIMS to provide information on the identity of these metal-organic complexes. With algorithms that search for isotopic patterns, we can determine the mass of metal-organic compounds within ESIMS spectra using natural abundance isotope distributions or through exchange experiments with a rare isotope spike.

Using these techniques, we have begun to explore the distribution and diversity of metal binding organic matter. In cultures, LC-ICPMS-ESIMS provides a method for rapid untargeted screening for metallophores that are produced for metal uptake and detoxification. We have identified new members of siderophore classes including synechobactins and marinobactins produced by cyanobacteria and heterotrophic bacteria. Applications to environmental samples have revealed a wide diversity of both known and new metal compounds that vary across nutrient regimes and influence metal bioavailability. The ability to map and characterize these compounds has opened up opportunities to better understand mechanisms that link metals with the microbes that use them.