Sticky marine bacteria

Roseobacters are a group of marine bacteria that interact with many different hosts in the ocean. Various Roseobacters are capable of physically attaching to their hosts, to each other and to various surfaces. A key question is how do these bacteria attach?

HFSP Long-Term Fellow Einat Segev and colleagues
authored on Mon, 30 November 2015

The Roseobacter clade is a significant group of bacteria in the ocean. These bacteria exhibit many different symbiotic life-styles. Numerous Roseobacters have extraordinary ability to attach themselves to both biotic and abiotic surfaces. When these bacteria attach to each other, they form multi-cellular structures called rosettes. Phaeobacter inhibens is a well-studied member of the Roseobacter clade. It exhibits diverse cell sizes and morphologies that are either associated with rosettes or appear as single cells.

Figure: Morphological heterogeneity in a population of Phaeobacter inhibens bacteria. Fluorescent membrane staining of the cells is shown in red and fluorescent lectin staining of the polar polysaccharide is shown in green. Note that the polysaccharide is seen at the poles of single cells and in the center of multi-cellular rosettes.

In the current study, we describe the various morphologies of a population of P. inhibens cells. We combine fluorescent membrane staining and a fluorescently labeled protein (a lectin) that stains a polar polysaccharide in P. inhibens, in order to characterize the various cell types and determine the complexity of individual rosettes. Synchronization of the cells in the bacterial population allowed us to explore the morphology of cells and various properties of rosettes over time. By using lectins with different fluorescent labels, we then study the kinetics of rosette formation. Finally, P. inhibens attachment to abiotic surfaces was examined using an attachment assay, allowing us to examine how attachment ability changes over time and how it can be hindered.

Our results reveal the broad pleomorphism of P. inhibens cells in nutrient rich medium with cell lengths ranging from one to ten microns.  Under these conditions, around 50% of the population was in rosettes whose complexity increased with time. A subset of the P. inhibens cells express a polar polysaccharide that is present in all rosette centers. We found no indication of rosette formation through cell division. Rather, we detected that rosettes form through cell-cell encounters. Cell adhesiveness to other bacterial cells as well as to an abiotic surface increased over time. Furthermore, the attachment of cells to the abiotic surface was perturbed by self-DNA from P. inhibens, but not by DNA from E. coli. Taken together, our results imply that the polar polysaccharide plays a role in bacterial adhesiveness but is likely to function in concert with other cellular mechanisms.

Reference

Morphological Heterogeneity and Attachment of Phaeobacter inhibens. Segev E, Tellez A, Vlamakis H, Kolter R. PLoS One. 2015 Nov 11;10(11):e0141300. doi: 10.1371/journal.pone.0141300.

Pubmed link