View article

Iron is an essential micronutrient often limiting the growth of marine microorganisms in wide areas of the world’s oceans. In high concentrations, iron, by contrast, is potentially toxic and usually leads to irreversible cell encrustation followed by cell death. To counteract both, microorganisms have evolved the strategy of producing organic iron-binding molecules, so called iron-ligands, enabling them to improve the bioavailability and uptake of iron as well as to mitigate its potentially toxic effects. Hydrothermal vents are among the major sources of iron in the oceans. These dynamic habitats host a variety of metabolically highly specialized and versatile microbes that not only have to cope with partially high iron concentrations but may also be able to mediate the availability of inorganic hydrothermal iron by actively producing iron-ligands. However, hardly any information exists to-date describing the impact of increasing iron concentrations on hydrothermal plume microbial communities and their potential to form iron-ligands. We therefore set up microcosm experiments with hydrothermal plume material in artificial seawater along an iron gradient ranging from 0 to 10 mM. We found that the microbial community at low iron concentrations (0.1 to 100 μM) differs significantly from that found in the original non-treated plume sample, allowing a certain group of Epsilonproteobacteria to become dominant (up to 93% of the overall community). The microbial community detected at 10 mM is by contrast more similar to that found in the original plume sample and consists mainly of one gammaproteobacterial group (up to 97% of the overall community). We further …