Mineral iron dissolution in Trichodesmium colonies: The role of O2 and pH microenvironments

Meri Eichner*, Subhajit Basu, Siyuan Wang, Dirk de Beer, Yeala Shaked

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

12 Scopus citations

Abstract

Colonies of the N2-fixing cyanobacterium Trichodesmium can harbor distinct chemical microenvironments that may assist the colonies in acquiring mineral iron from dust. Here, we characterized O2 and pH gradients in and around Trichodesmium colonies by microsensor measurements on > 170 colonies collected in the Gulf of Eilat over ∼ 2 months. O2 concentrations and pH values in the center of single colonies decreased in the dark due to respiration, reaching minimum values of 70 μmol L−1 and 7.7, whereas in the light, O2 and pH increased due to photosynthesis, reaching maximum values of 410 μmol L−1 and 8.6. Addition of dust and bacteria and increasing colony size influenced O2 and pH levels in the colonies, yet values remained within the range observed in single natural colonies. However, lower values down to 60 μmol L−1 O2 and pH 7.5 were recorded in the dark in dense surface accumulations of Trichodesmium. Using radiolabelled ferrihydrite, we examined the effect of these conditions on mineral iron dissolution and availability to Trichodesmium. Dark-incubated colonies did not acquire iron from ferrihydrite faster than light-incubated colonies, indicating that the dark-induced decrease in pH and O2 within single colonies is too small to significantly increase mineral iron bioavailability. Yet, ligand-promoted dissolution of ferrihydrite, a mechanism likely applied by Trichodesmum for acquiring mineral iron, did increase at the lower pH levels observed in surface accumulations. Thus, Trichodesmium surface blooms in their final stage may harbor chemical conditions that enhance the dissolution and bioavailability of mineral iron to the associated microbial community.

Original languageAmerican English
Pages (from-to)1149-1160
Number of pages12
JournalLimnology and Oceanography
Volume65
Issue number6
DOIs
StatePublished - 1 Jun 2020

Bibliographical note

Publisher Copyright:
© 2019 The Authors. Limnology and Oceanography published by Wiley Periodicals, Inc. on behalf of Association for the Sciences of Limnology and Oceanography.

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