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Aquatic Microbial Ecology

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AME 42:19-26 (2006)  -  doi:10.3354/ame042019

Interactions between marine snow and heterotrophic bacteria: aggregate formation and microbial dynamics

H. P. Grossart1,*, T. Kiørboe2, K. W. Tang3, M. Allgaier1, E. M. Yam3, H. Ploug4

1Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB), Alte Fischerhuette 2, 16775 Stechlin, Germany
2Danish Institute for Fisheries Research, Kavalergården 6, 2920 Charlottenlund, Denmark
3Virginia Institute of Marine Science, Gloucester Point, Virginia 23062, USA
4Max Planck Institute for Marine Microbiology, Celsiusstrasse 1, 28359 Bremen, Germany

ABSTRACT: Macroscopic aggregates (marine snow) contribute to new production and nutrient dynamics in the upper ocean and vertical fluxes of organic matter to the deep ocean. To test whether microorganisms play a significant role in phytoplankton aggregate formation we studied particle abundance and size as well as abundance, colonization behaviour, and community composition of bacteria during the growth of 2 marine diatoms (Thalassiosira weissflogii and Navicula sp.) under axenic and non-axenic conditions. Community composition of free-living and attached bacteria during phytoplankton growth and aggregation was studied by amplification of 16S rRNA gene fragments and denaturing gradient gel electrophoresis (DGGE). Our results show that the presence of bacteria was a prerequisite for aggregation of T. weissflogii but not of Navicula sp. Occurrences of distinct populations of free-living and attached bacteria depended on phytoplankton growth and aggregation dynamics. The community composition of especially attached bacteria significantly differed between the 2 algal cultures. Our study suggests that phytoplankton aggregation and vertical fluxes are closely linked to interactions between the marine phytoplankton and the ambient microbial community.

KEY WORDS: Heterotrophic bacteria · Marine diatoms · Aggregates · DGGE · Image analysis · Bacterial behaviour

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