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MEPS 461:1-14 (2012)  -  DOI:

Effects of Marinobacter adhaerens HP15 on polymer exudation by Thalassiosira weissflogii at different N:P ratios

Astrid Gärdes1,4, Yannic Ramaye1, Hans-Peter Grossart2, Uta Passow3, Matthias S. Ullrich1,*

1Jacobs University Bremen, Molecular Life Science Research Center, Campus Ring 1, 28759 Bremen, Germany
2Leibniz Institute of Freshwater Ecology and Inland Fisheries, Alte Fischerhuette 2, 16775 Stechlin, Germany
3Marine Science Institute, University of California - Santa Barbara, Santa Barbara, California 93106, USA
4Present address: San Diego State University, Department of Chemistry and Biochemistry, 5500 Campanile Drive, San Diego, California 92182, USA

ABSTRACT: In the ocean, exopolymer accumulation and the resulting aggregation of marine phytoplankton drive the flux of sinking organic matter. Little is known about the contribution of bacteria to the release and build-up of such exudates. We describe an in-depth investigation of exopolymer production under differing nutrient conditions using a diatom−bacteria model system. Responses of the marine diatom Thalassiosira weissflogii to different nutrient regimes and the impact of the co-incubated bacterium Marinobacter adhaerens on algal exudation were evaluated by analyzing quantity and quality of exudation products. Cultures of T. weissflogii were grown at nutrient-balanced conditions (Redfield ratio N:P = 16) as well as at nitrogen- or phosphorus-depleted conditions (N:P = 1 and N:P = 95, respectively) in the presence or absence of M. adhaerens. The impact of M. adhaerens on the concentration of dissolved organic carbon and transparent exopolymer particles (TEP), as well as on the composition of amino acids and carbohydrates, depended on the nutrient regime. Under nutrient-balanced conditions, M. adhaerens stimulated both T. weissflogii growth and TEP production. Under nutrient-depleted conditions, TEP production was enhanced regardless of whether bacteria were present. Phosphorus limitation resulted in an appreciable change in the %mol composition of dissolved amino acids in xenic and axenic treatments. Differential lectin staining revealed that the presence of M. adhaerens enhanced and modified the production of specific extracellular substances. A better understanding of the effects of diatom−bacteria interactions on the accumulation of exudation products is crucial in modelling and predicting consequences of environmental changes on oceanic organic matter and nutrient cycling.

KEY WORDS: Diatom-bacteria interactions ·Transparent exopolymer particles · TEP · Dissolved organic carbon · Nutrient limitation · Lectin staining · Marino bacter adhaerens · Thalassiosira weissflogii

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Cite this article as: Gärdes A, Ramaye Y, Grossart HP, Passow U, Ullrich MS (2012) Effects of Marinobacter adhaerens HP15 on polymer exudation by Thalassiosira weissflogii at different N:P ratios. Mar Ecol Prog Ser 461:1-14.

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