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Aquatic Microbial Ecology

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AME 83:295-308 (2019)  -  DOI: https://doi.org/10.3354/ame01919

Shifts in cell size and community composition of bacterioplankton due to grazing by heterotrophic flagellates: evidence from a marine system

Markus G. Weinbauer1,*, Saara Suominen1, Jan Jezbera2, Marie-Emanuelle Kerros1, Sophie Marro1, John R. Dolan1, Karel Šimek2

1Sorbonne Universités, UPMC, Université Paris 06, CNRS, Laboratoire d’Océanographie de Villefranche (LOV), 181 Chemin du Lazaret, 06230 Villefranche-sur-Mer, France
2Biology Centre CAS, v.v.i., Hydrobiological Institute, Na Sádkách 7, 37005 Céské Budéjovice, Czech Republic
*Corresponding author:

ABSTRACT: The effect of flagellate grazing on bacterioplankton community composition, e.g. cell size and diversity, has been well studied in fresh waters, but much less is known for marine systems. We conducted experiments with communities from an oligotrophic bay in the NW Mediterranean Sea; size fractionation was used to alter grazing by flagellates, and incubation in dialysis bags was used to retain otherwise in situ conditions. Grazing reduced bacterial abundance and growth. In contrast to a current model of the effects of grazing, cell size distribution was unimodal and not bimodal. Significant shifts towards larger cell size classes were observed. This is in accordance with the idea that increasing the cell length is a bacterial strategy to reduce susceptibility to grazing by small flagellates. Only weak evidence was found for the complementary strategy of reducing cell size. In all experiments, bacterial community structure as assessed by PCR-based 16S rRNA gene denaturing gradient gel electrophoresis (DGGE) showed significant differences associated with the presence of grazers. Sequence analyses of DGGE bands were used to select probes for catalyzed reporter deposition-fluorescence in situ hybridization analysis for specific taxa. In our experiments, Polaribacter showed patterns of defense against grazing, while Roseobacter was highly susceptible to grazing. Although the effect of grazing may be stronger in freshwater than in oligotrophic marine systems, our data support the hypotheses that (1) increasing the cell size is a bacterial defense strategy against grazing by small flagellates typical in marine systems and (2) grazing influences bacterial community composition.


KEY WORDS: Flagellates · Bacteria · Diversity · Life strategies · Grazing defense


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Cite this article as: Weinbauer MG, Suominen S, Jezbera J, Kerros ME, Marro S, Dolan JR, Šimek K (2019) Shifts in cell size and community composition of bacterioplankton due to grazing by heterotrophic flagellates: evidence from a marine system. Aquat Microb Ecol 83:295-308. https://doi.org/10.3354/ame01919

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