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Bioavailable iron titrations reveal oceanic Synechococcus ecotypes optimized for different iron availabilities

Gilbert, NE, LeCleir, GR, Strzepek, RF ORCID: 0000-0002-6442-7121, Ellwood, MJ, Twining, BS, Roux, S, Pennacchio, C, Boyd, PW ORCID: 0000-0001-7850-1911 and Wilhelm, SW 2022 , 'Bioavailable iron titrations reveal oceanic Synechococcus ecotypes optimized for different iron availabilities' , ISME Communications, vol. 2 , pp. 1-12 , doi:

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The trace metal iron (Fe) controls the diversity and activity of phytoplankton across the surface oceans, a paradigm established through decades of in situ and mesocosm experimental studies. Despite widespread Fe-limitation within high-nutrient, low chlorophyll (HNLC) waters, significant contributions of the cyanobacterium Synechococcus to the phytoplankton stock can be found. Correlations among differing strains of Synechococcus across different Fe-regimes have suggested the existence of Fe-adapted ecotypes. However, experimental evidence of high- versus low-Fe adapted strains of Synechococcus is lacking, and so we investigated the transcriptional responses of microbial communities inhabiting the HNLC, sub-Antarctic region of the Southern Ocean during the Spring of 2018. Analysis of metatranscriptomes generated from on-deck incubation experiments reflecting a gradient of Fe-availabilities reveal transcriptomic signatures indicative of co-occurring Synechococcus ecotypes adapted to differing Fe-regimes. Functional analyses comparing low-Fe and high-Fe conditions point to various Fe-acquisition mechanisms that may allow persistence of low-Fe adapted Synechococcus under Fe-limitation. Comparison of in situ surface conditions to the Fe-titrations indicate ecological relevance of these mechanisms as well as persistence of both putative ecotypes within this region. This Fe-titration approach, combined with transcriptomics, highlights the short-term responses of the in situ phytoplankton community to Fe-availability that are often overlooked by examining genomic content or bulk physiological responses alone. These findings expand our knowledge about how phytoplankton in HNLC Southern Ocean waters adapt and respond to changing Fe supply.

Item Type: Article
Authors/Creators:Gilbert, NE and LeCleir, GR and Strzepek, RF and Ellwood, MJ and Twining, BS and Roux, S and Pennacchio, C and Boyd, PW and Wilhelm, SW
Keywords: iron, Southern Ocean, cyanobacteria, ecotype, physiology, transcriptomics
Journal or Publication Title: ISME Communications
Publisher: Nature Publishing Group
ISSN: 2730-6151
DOI / ID Number:
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© 2022. The Authors. This article is licensed under a Creative Commons Attribution 4.0 International (CC BY 4.0) License, (, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

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