Astrid Gärdes


gaerdesExperimental model system for diatom-bacteria interactions

Marine bacteria and algae are the numerically most dominant organism groups in upper ocean layers and thus have a large impact on assimilation of atmospheric carbon dioxide, nutrient cycling, and energy flow in pelagic eco-systems. Aggregation of diatoms is an important process for the assimilation of particulate organic carbon in form of marine snow. Exudation products of phytoplankton are rich in acidic polysaccharides and can form transparent exopolymer particles (TEP), which are important agents for aggregation and thus act as precursors of marine snow particles. Heterotrophic bacteria interacting with diatoms are important for controlling the aggregation of phytoplankton. In this context, bacterial impact on TEP formation has not been explored in detail. A large pool of algae- and particle-associated marine bacterial isolates was tested with regard to adherence to the diatom, Thalassosira weissflogii. An attachment assay was developed and used to reproducibly identify attaching bacterial strains, which were then analyzed in rolling tank experiments with respect to TEP and aggregate formation. Plasmid conjugation and mutational experiments are conducted to test the genetic accessibility of the bacterial strains. Our work aims at establishing an experimental model system to investigate bacteria-diatom interactions, bacterial adhesion, and the contribution of bacterial attachment to marine aggregate formation using genetic tools. It thus will be used for molecular in-depth analyses of genes and gene products associated with this interaction.

image002-109x90-146x105Bright-field microscopy of TEP visualized using alcian blue strain



image003Scanning electron microscopy (SEM) of the diatom T. weissflogii with attaching bacteria