Patterns of iron and siderophore distributions across the California Current System

Abstract

Coastal upwelling of nutrients and metals along eastern boundary currents fuels some of the most biologically productive marine ecosystems. Although iron is a main driver of productivity in many of these regions, iron cycling and acquisition by microbes remain poorly constrained, in part due to the unknown composition of organic ligands that keep bioavailable iron in solution. In this study, we investigated organic ligand composition in discrete water samples collected across the highly productive California Coastal upwelling system. Siderophores were observed in distinct nutrient regimes at concentrations ranging from 1 pM to 18 pM. Near the shallow continental shelf, ferrioxamine B was observed in recently upwelled, high chlorophyll surface waters while synechobactins were identified within nepheloid layers at 60–90 m depth. In offshore waters characterized by intermediate chlorophyll, iron, and nitrate concentrations, we found amphibactins and an unknown siderophore with a molecular formula of C33H58O8N5Fe. Highest concentrations were measured in the photic zone, however, amphibactins were also found in waters as deep as 1500 m. The distribution of siderophores provides evidence for microbial iron deficiency across a range of nutrient regimes and indicates siderophore production and acquisition is an important strategy for biological iron uptake in iron limited coastal systems. Polydisperse humic ligands were also detected throughout the water column and were particularly abundant near the benthic boundary. Our results highlight the fine‐scale spatial heterogeneity of metal ligand composition in an upwelling environment and elucidate distinct sources that include biological production and the degradation of organic matter in suboxic waters.

Reduction-dependent siderophore assimilation in a model pennate diatom

“…DFOB and L 1 exhibit a similar affinity for free Fe(III) (21). DFOB is also known to be produced by marine bacteria (22) and in recent studies, which have conducted direct measurements of siderophores in seawater, DFOB has been detected in coastal eutrophic and offshore oligotrophic environments (23, 24). Therefore, DFOB appears to be a reasonable option in assays or experimentation where an L 1 analog is needed.…”

Rain-fed streams dilute inorganic nutrients but subsidise organic matter-associated nutrients in coastal waters of the northeast Pacific Ocean

“…Terrestrial dissolved organic matter-bound Fe, which likely predominates in these watersheds, has been shown to be highly stable during estuarine mixing, and can be transported well beyond the estuary to open waters where it can serve as a source of potentially limiting-Fe (Herzog et al, 2020b). However, despite this stability, these complexes remain permeable to microbial siderophores (Batchelli et al, 2010), molecules with a strong affinity for Fe produced by microbes across a wide diversity of nutrient regimes in the coastal oceans (Boiteau et al, 2019). The quantification of dFe complexation and more broadly of fate (sedimentation, uptake) are important next steps within this region (Fig.…”

Incorporation of Hydroxamate Siderophore and Associated Fe Into Marine Particles in Natural Seawater

“…In response to the scarcity of Fe, microorganisms produce a variety of Fe-binding ligands, e.g., siderophores, that create highly soluble forms of dFe by chelation that are then transformed to bioavailable Fe through microbial enzymatic solubilization reactions (Morel and Price, 2003;Gledhill and Buck, 2012;Hassler et al, 2015). As a consequence, essentially ≥99% of dFe in the ocean is complexed by naturally occurring organic ligands, of which some have been characterized as siderophores (Butler, 2005;Mawji et al, 2008;Boiteau et al, 2016Boiteau et al, , 2019Bundy et al, 2018;Yarimizu et al, 2019).…”