Cell shape modification as novel buoyancy control mechanism of marine Roseobacter bacteria

The Roseobacter group (class Alphaproteobacteria)- accounts for up to 25% of the bacterial community in marine habitats. Members of this group are physiologically versatile, which can be regarded as prerequisite for an adaptation to different ecological niches. In a constantly changing environment, they can exploit transient nutrient pulses and thereby successfully compete against microorganisms inhabiting the same habitat. Morphological heterogeneity is another common trait in the Roseobacter group. Morphotypes range from rod- shaped single cells of variable length to multicellular rosettes and filaments. For Dinoroseobacter shibae it has been shown that cell elongation is regulated by quorum sensing[1].

Here, we present evidence that for Phaeobacter inhibens DSM 17395, a common model organism of the Roseobacter group and successful colonizer of marine surfaces, there are triggers for cell elongation- decoupled from studied quorum sensing mechanisms. Using time-lapse microscopy experiments and quantitative image analysis we show that P. inhibens undergoes morphological changes in response to the presence of yeast and algal extracts. We demonstrate that the longitudinal cell elongation increases the buoyancy of the bacterial cells. The phenotype was still observed for a P. inhibens mutant strains devoid of the cell cycle ranscriptional regulator gene ctrA. Removing the eukaryotic trigger by medium exchange results in an immediate reinitiation of cell division and reversal of the elongated cell morphotype back to rod- shaped single cells and rosettes. We hypothesize that P. inhibens uses cell shape modifications to control buoyancy in a nutrient-rich zone and to enlargen the surface are for attachment.

[1] D. Patzelt, H. Wang, I. Buchholz, M. Rohde, L. Gröbe, S. Pradella, A. Neumann, S. Schulz, S. Heyber, K. Münch, R. Münch, D. Jahn, I. Wagner-Döbler, J. Tomasch, You are what you talk: quorum sensing induces individual morphologies and cell division modes in Dinoroseobacter shibae, The ISME Journal, 7 (2013) 2274-2286.