Biological production of ligands influences iron chemistry in hydrothermal systems

7 January 2025

For the first time, siderophores and siderophore-producing microbes were determined in 11 geochemically distinct hydrothermal plume environments along the Mid-Atlantic Ridge. A striking feature in this study, proposed by Hoffman and colleagues (2024, see reference below), is the broad variety of hydrothermal vent environments studied; from alkaline -very low iron (Fe) to acidic-high temperature-high Fe plumes, along with samples that were collected both near-field (<100 km from the vent) and diffuse environments around vent fields.

At sites where strong Fe-binding organic ligands (L₁) were detected, the authors showed that dissolved Fe concentrations were tightly coupled to L₁ ligands in a nearly 1:1 ratio, and that siderophores were a portion of the L₁ ligands coupled to dissolved Fe in the neutrally-buoyant plume. They reveal the presence of amphiphilic siderophores and siderophore-producing bacteria in the samples may point to microbial utilization of siderophores to access particulate hydrothermal iron, and the exchange of dissolved and particulate iron within hydrothermal plumes.

**Figure:** (A) Map of the study area where hydrothermal vents were studied along the Mid-Atlantic Ridge. (B) The concentrations of dissolved iron (Fe) and organic ligands (L₁) in the neutrally-buoyant plumes of the study region. Some of the ligands detected were siderophores (C), organic compounds produced by bacteria to access Fe. A variety of siderophore types were detected (D), including amphiphilic siderophores (E) that are common in the marine environment.

Reference:

Hoffman, C. L., Monreal, P. J., Albers, J. B., Lough, A. J. M., Santoro, A. E., Mellett, T., Buck, K. N., Tagliabue, A., Lohan, M. C., Resing, J. A., & Bundy, R. M. (2024). Microbial strong organic-ligand production is tightly coupled to iron in hydrothermal plumes. Biogeosciences, 21, 5233–5246. Access the paper: 10.5194/bg-21-5233-2024

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