The Response of Heterotrophic Prokaryote and Viral Communities to Labile Organic Carbon Inputs Is Controlled by the Predator Food Chain Structure

• Published in: Viruses
• Main Authors: Ruth-Anne Sandaa, Bernadette Pree, Aud Larsen, Selina Våge, Birte Töpper, Joachim P. Töpper, Runar Thyrhaug, Tron Frede Thingstad
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2017
• Subjects: marine viral diversity; viral–host interaction; high latitude microbes; minimum food web model; copepods; ciliates; nutrient limitation; trophic cascade; Microbiology; QR1-502; Arctic; Copepods
• Online Access: https://doi.org/10.3390/v9090238; https://doaj.org/article/8e00caa562b547c2a58a7d4be07b930c

Factors controlling the community composition of marine heterotrophic prokaryotes include organic-C, mineral nutrients, predation, and viral lysis. Two mesocosm experiments, performed at an Arctic location and bottom-up manipulated with organic-C, had very different results in community composition for both prokaryotes and viruses. Previously, we showed how a simple mathematical model could reproduce food web level dynamics observed in these mesocosms, demonstrating strong top-down control through the predator chain from copepods via ciliates and heterotrophic nanoflagellates. Here, we use a steady-state analysis to connect ciliate biomass to bacterial carbon demand. This gives a coupling of top-down and bottom-up factors whereby low initial densities of ciliates are associated with mineral nutrient-limited heterotrophic prokaryotes that do not respond to external supply of labile organic-C. In contrast, high initial densities of ciliates give carbon-limited growth and high responsiveness to organic-C. The differences observed in ciliate abundance, and in prokaryote abundance and community composition in the two experiments were in accordance with these predictions. Responsiveness in the viral community followed a pattern similar to that of prokaryotes. Our study provides a unique link between the structure of the predator chain in the microbial food web and viral abundance and diversity.