Speaker
Description
Members of the Roseobacter group (class Alphaproteobacteria) can account for up to 25% of the bacterial community in marine ecosystems. They are physiologically versatile, which can be regarded as prerequisite for an adaptation to different ecological niches. Members of the group are morphologically heterogeneous and either form rod- shaped single cells of variable length or multicellular rosettes. Here, we identified triggers for cell elongation in the heterotrophic model strain Phaeobacter inhibens that appear to function in independence of previously studied quorum sensing mechanisms. Using time-lapse microscopy and quantitative image analysis we show that P. inhibens undergoes morphological changes in response to the presence of eukaryotic cells or culture extracts, for example of algae and lysed diatoms. Similar effects were observed with medium containing yeast extract. The longitudinal cell elongation presumably increases the buoyancy of the bacterial cells. Reversal of the morphological phenotype was achieved by removing the trigger with a medium exchange. Continuing cultivation in medium without eukaryotic material results in immediate reinitiation of cell division: elongated cells turn back to rod- shaped single cells and rosettes. We thus hypothesize that P. inhibens uses cell shape modifications to control buoyancy and to enlargen the surface for attachment in nutrient-rich zones.
