Abstract
Siderophores are low-molecular-weight metal chelators that function in microbial iron uptake. As iron limits primary productivity in many environments, siderophores are of great ecological importance. Additionally, their metal binding properties have attracted interest for uses in medicine and bioremediation. Here, we review the current state of knowledge concerning the siderophores produced by cyanobacteria. We give an overview of all cyanobacterial species with known siderophore production, finding siderophores produced in all but the most basal clades, and in a wide variety of environments. We explore what is known about the structure, biosynthesis, and cycling of the cyanobacterial siderophores that have been characterized: Synechobactin, schizokinen and anachelin. We also highlight alternative siderophore functionality and technological potential, finding allelopathic effects on competing phytoplankton and likely roles in limiting heavy-metal toxicity. Methodological improvements in siderophore characterization and detection are briefly described. Since most known cyanobacterial siderophores have not been structurally characterized, the application of mass spectrometry techniques will likely reveal a breadth of variation within these important molecules.
Highlights
Cyanobacteria rely on iron as an essential cofactor for performing oxygenic photosynthesis and have much larger iron requirements than non-photosynthetic organisms [1]
Cyanobacteria use siderophores to outcompete other organisms as antimicrobial agents and to protect themselves from heavy-metal toxicity. These properties make them of biotechnological interest, and concepts have been demonstrated where cyanobacterial siderophores are used for antimicrobial coating materials and for uranium sequestration
Considering the ecological significance of iron uptake by plankton, it is surprising that so few cyanobacterial siderophores have been characterized
Summary
Cyanobacteria rely on iron as an essential cofactor for performing oxygenic photosynthesis and have much larger iron requirements than non-photosynthetic organisms [1]. In large swaths of the ocean, iron availability is rate-limiting for the growth of cyanobacteria and other phytoplankton These regions, termed “high-nitrogen, low chlorophyll” (HNLC), have attracted interest as targets for iron fertilization interventions as a way of increasing carbon sequestration and potentially counteracting climate change [5,6]. The diffusive loss of the siderophores would make for an energetically costly method of iron sequestration that does not directly benefit the siderophore producer It appears that low-iron, open ocean environments show high concentrations of amphiphilic siderophore variants, that may limit diffusive losses due to association with the cell membrane [18]. These properties make them of biotechnological interest, and concepts have been demonstrated where cyanobacterial siderophores are used for antimicrobial coating materials and for uranium sequestration
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