Phytoplankton exudates provide full nutrition to a subset of accompanying heterotrophic bacteria via carbon, nitrogen and phosphorus allocation

Falk Eigemann, Eyal Rahav, Hans Peter Grossart, Dikla Aharonovich, Daniel Sher, Angela Vogts, Maren Voss

Research output: Contribution to journalArticlepeer-review

9 Scopus citations

Abstract

Marine bacteria rely on phytoplankton exudates as carbon sources (DOCp). Yet, it is unclear to what extent phytoplankton exudates also provide nutrients such as phytoplankton-derived N and P (DONp, DOPp). We address these questions by mesocosm exudate addition experiments with spent media from the ubiquitous pico-cyanobacterium Prochlorococcus to bacterial communities in contrasting ecosystems in the Eastern Mediterranean – a coastal and an open-ocean, oligotrophic station with and without on-top additions of inorganic nutrients. Inorganic nutrient addition did not lower the incorporation of exudate DONp, nor did it reduce alkaline phosphatase activity, suggesting that bacterial communities are able to exclusively cover their nitrogen and phosphorus demands with organic forms provided by phytoplankton exudates. Approximately half of the cells in each ecosystem took up detectable amounts of Prochlorococcus-derived C and N, yet based on 16S rRNA sequencing different bacterial genera were responsible for the observed exudate utilization patterns. In the coastal community, several phylotypes of Aureimarina, Psychrosphaera and Glaciecola responded positively to the addition of phytoplankton exudates, whereas phylotypes of Pseudoalteromonas increased and dominated the open-ocean communities. Together, our results strongly indicate that phytoplankton exudates provide coastal and open-ocean bacterial communities with organic carbon, nitrogen and phosphorus, and that phytoplankton exudate serve a full-fledged meal for the accompanying bacterial community in the nutrient-poor eastern Mediterranean.

Original languageEnglish
Pages (from-to)2467-2483
Number of pages17
JournalEnvironmental Microbiology
Volume24
Issue number5
DOIs
StatePublished - May 2022
Externally publishedYes

Bibliographical note

Publisher Copyright:
© 2022 The Authors. Environmental Microbiology published by Society for Applied Microbiology and John Wiley & Sons Ltd.

Funding

We thank two reviewers for valuable input, the captain and crew of the R/V Mediterranean Explorer (EcoOcean) for help at sea, Mike Krom, Anat Tsemel and Tal Ben‐Ezra for the inorganic nutrient analysis, and Stefan Green (DNA Services Facility at the University of Illinois at Chicago) for the amplicon sequencing. We also thank Tom Reich, Dalit Roth‐Rosenberg, Tal Luzzatto‐Knaan, Noam Nago and Natalia Belkin for excellent help with the experiments, and Annett Grüttmüller for NanoSIMS measurements. This work was supported by the Human Frontier Science Program (HFSP) through the grant number RGB 0020/2016 (DS, MV and HPG), by the National Science Foundation – United States‐Israel Binational Science Foundation Program in Oceanography (grant number 1635070/2016532 to DS) and by the Israel Ministry of Science and Technology (grant number 3‐17404 to DS). The experiment at THEMO‐2 was performed as part of the SoMMoS (Southeastern Mediterranean Monthly cruise Series) project, with ship‐time funded by the Leon H. Charney School of Marine Sciences with help from EcoOcean and IOLR. The NanoSIMS at the Leibniz Institute for Baltic Sea research in Warnemuende (IOW) was funded by the German Federal Ministry of Education and Research (BMBF), grant identifier 03F0626A.

FundersFunder number
IOLR
Leibniz Institute for Baltic Sea Research
National Science Foundation
Human Frontier Science ProgramRGB 0020/2016
United States-Israel Binational Science Foundation1635070/2016532
Bundesministerium für Bildung und Forschung03F0626A
Ministry of science and technology, Israel3‐17404

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