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Contact
Dr. Kai Thormann
MPI für terrestrische Mikrobiologie
Karl-von-Frisch-Straße
D-35043 Marburg / Germany
Phone: +49 6421 178301
Fax: +49 6421 178309
E-mail:
thormann@mpi-marburg.mpg.de

Biofilms and Motility of Shewanella

Our group is using a model organism for microbial metal reduction, Shewanella oneidensis MR-1, to study regulatory systems and the underlying environmental signals that lead to the formation of cell-surface interactions and influence the dynamics of community formation. S. oneidensis MR-1 is a versatile organism that can thrive in a wide range of environmental conditions and is capable of using an impressive array of alternative terminal electron acceptors, including metal oxides. In many cases, altering of the metal’s reduction state results in drastic changes in solubility, leading for example not only to a corrosion of ferric and manganese minerals but also to precipitation of highly soluble chromium and uranium salts. Thus, S. oneidensis MR-1 has huge potential to be used in bioremediation processes.

To study bacterial life on surfaces, we have established and adapted systems that allow us to monitor S. oneidensis MR-1 by means of confocal laser scanning and fluorescent microscopy.(Fig. 1). Although sometimes resembling developmental cycles, community formation of S. oneidensis MR-1 is a dynamic process responding to environmental cues but lacking a specific genetic program.

Shadow projection of CLSM images of a biofilm formed by <i>Shewanella oneidensis</i> MR-1 after 72h (100 kb)

Fig 1. Shadow projection of CLSM images of a biofilm formed by Shewanella oneidensis MR-1 after 72h. The cells are labeled with Yfp and Cfp, respectively.

Initiation of cell-surface interactions

In general, bacterial community formation starts with single cells attaching to a substratum and becoming permanently immobilized. This initial attachment marks the onset of the bacterial life style switch, sets the stage for subsequent community formation, and enables cells to directly interact with the surface. Regulatory events and underlying environmental signals following bacterial surface attachment that mediate the life-style switch are still mostly unknown. This represents one of the major topics our group is currently interested in.

We have developed a cell harvesting system that allows the isolation of cells that are individually attached to a substratum. Cells harvested from this system are currently being used for general transcriptomic and proteomic profiling of initial attachment events. The initial results suggest that, upon attachment, S. oneidensis MR-1 undergoes extensive metabolic rearrangement prior to the formation of three-dimensional structures. Since S. oneidensis MR-1 can directly interact with redox-active surfaces, such as iron oxides, we are also investigating the attachment response to different, metabolically accessible surfaces to determine whether a surface recognition, a 'surface sensing', exists and which regulatory systems might be involved in that process.

Role of flagella-mediated motility for S. oneidensis

Previous characterization of transposon-derived mutants of S.oneidensis MR-1 exhibiting defects in early community formation identified a number of factors affecting initial attachment. A significant number of these mutants were found to be affected in flagella-mediated swimming motility. In liquid environments, S. oneidensis MR-1 is propelled by a single polar flagellum. Flagellamediated motility is not essential for the cells to reach the surface but appears to play a major role in the subsequent transition from planktonic to surface-associated life-style (Fig.2). This phenomenon is widespread among flagellated bacteria. We are currently investigating the mechanism that enables S. oneidensis MR-1 to use its polar flagellum in the process of sensing surface contact.

Intriguingly, according to the genome data the organism possesses two stator systems to drive flagella rotation that depend on different ion gradients. We have demonstrated that both systems are simultaneously expressed and thus might form a hybrid motor system. In the future, we are planning to further investigate the functional roles of, and interplay between, the two stator complexes and determine how they contribute to the transition between sessile and planktonic life style.

Schematic model of the flagellar motor system (42 kb)
Fig.2 Left: Schematic model of the flagellar motor system (OM, outer membrane; PG, peptidoglycane/cell wall; CM, cytoplasmic membrane). Right: localization of the PomB stator subunits: A) fluorescence image/DIC image; B) overlay