Dust is an important iron (Fe) source to the ocean, but its utilization by phytoplankton is constrained by rapid sinking and slow dissolution dust-bound iron (dust-Fe). Colonies of the globally important cyanobacterium, Trichodesmium, overcome these constraints by efficient dust capturing and active dust-Fe dissolution. In this study we examined the ability of Trichodesmium colonies to maximize their Fe supply from dust by selectively collecting Fe-rich particles. Testing for selectivity in particle collection, we supplied ~600 individual colonies, collected on multiple days from the Gulf of Aqaba, with natural dust and silica minerals that were either cleaned of or coated with Fe. Using a stereoscope, we counted the number of particles retained by each colony shortly after addition and following 24 h incubation with particles, and documented translocation of particles to the colony core. We observed a strong preference for Fe-rich particles over Fe-free particles in all tested parameters. Moreover, some colonies discarded the Fe-free particles they initially collected. The preferred collection of Fe-rich particles and disposal of Fe-free particles suggest that Trichodesmium can sense Fe and selectively choose Fe-rich dust particles. This ability assists Trichodesmium obtain Fe from dust and facilitate its growth and subsequent contribution to nutrient cycling and productivity in the ocean.
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Acknowledgements The authors sincerely thank Murielle Dray (IUI) and Nir Keren (Hebrew University) for valuable assistance during the study. YS and her group were supported by the Israel Science Foundation grant 458/15 (www.isf.org.il) and the German-Israeli Foundation for Scientific Research and Development grant #1349 (www.GIF. org.il). RKS and PKW were supported by Laboratory Directed Research and Development (LDRD) funding (16-LW-030), and that portion of the work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. SB acknowledges PBC Postdoctoral fellowship for Indian researchers and SW acknowledges NSFC-HUJI doctoral fellowship for Chinese researchers.
© 2019, The Author(s).