Exopolymeric Substances Control Microbial Community Structure and Function by Contributing to both C and Fe Nutrition in Fe-Limited Southern Ocean Provinces

• Published in: Microorganisms
• Main Authors: Sonia Blanco-Ameijeiras, Damien J. E. Cabanes, Rachel N. Cable, Scarlett Trimborn, Stéphan Jacquet, Sonja Wiegmann, Christian Völkner, Florian Lelchat, Astrid Bracher, Melissa B. Duhaime, Christel S. Hassler
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2020
• Subjects: virus; prokaryotes; phytoplankton; Southern Ocean; exopolymeric substances; iron; Biology (General); QH301-705.5; Drake Passage
• Online Access: https://doi.org/10.3390/microorganisms8121980; https://doaj.org/article/6a16615022d44b32a15c4e2ac2628f17

Organic ligands such as exopolymeric substances (EPS) are known to form complexes with iron (Fe) and modulate phytoplankton growth. However, the effect of organic ligands on bacterial and viral communities remains largely unknown. Here, we assessed how Fe associated with organic ligands influences phytoplankton, microbial, and viral abundances and their diversity in the Southern Ocean. While the particulate organic carbon (POC) was modulated by Fe chemistry and bioavailability in the Drake Passage, the abundance and diversity of microbes and viruses were not governed by Fe bioavailability. Only following amendments with bacterial EPS did bacterial abundances increase, while phenotypic alpha diversity of bacterial and viral communities decreased. The latter was accompanied by significantly enhanced POC, pointing toward the relief of C limitation or other drivers of the microbial loop. Based on the literature and our findings, we propose a conceptual framework by which EPS may affect phytoplankton, bacteria, and viruses. Given the importance of the Southern Ocean for Earth’s climate as well as the prevalence of viruses and their increasingly recognized impact on marine biogeochemistry and C cycling; the role of microbe–virus interactions on primary productivity in the Southern Ocean needs urgent attention.