Nora Ausmees

My active scientific career began in 1997, when I started PhD studies at the Swedish University of Agricultural Sciences (SLU). During this period, I developed a deeper interest in bacterial cell architecture. My interest was triggered initially by a surprising finding of polar asymmetry in a seemingly symmetric rod-shaped bacterium, the plant endosymbiont Rhizobium leguminosarum. Our work yielded a model of polar attachment of rhizobium bacteria to the root hairs using a unipolar adhesive structure of lectins and cellulose fibers. We also showed for the first time that the so-called GGDEF domains (widespread but cryptic modules in bacterial signaling proteins), in fact possess catalytic activity for the synthesis of a novel secondary messenger molecule cyclic di-GMP.
Immediately after receiving the PhD degree I joined Dr. Christine Jacobs-Wagner at Yale University as a Postdoctoral Fellow to continue studying bacterial cell architecture in another model organism - a ubiquitous aquatic bacterium Caulobacter crescentus. This research resulted in the discovery of crescentin – a novel bacterial cytoskeletal element which determined the characteristic shape of C. crescentus cells and strikingly resembled the intermediate filaments (IF) of eukaryotic cells. This was a striking and unexpected finding, because actin- and tubulin-related proteins were known to exist in bacteria, but IFs were considered as an exclusively metazoan invention. I have continued studies of bacterial cytoskeleton and cell architecture as an Assistant Professor at Uppsala University, and presently at Lund University.

My long-term scientific goal is to study and understand how bacteria go about to translate the linear genetic information into a three-dimensional structure of the cells. This is a basic biological task that all organisms face, but it has traditionally been studied mainly in the context of eukaryotic cells. However, the last decade has witnessed an explosion of interest in the cellular organization of bacteria by the international research community. We are beginning to understand that a large variety of cytoskeletal elements exist in bacteria and are needed for vital cellular functions, such as growth, division and morphology. My specific interest is in the intermediate filament-like coiled coil cytoskeleton of bacteria. Over 30 human diseases have been linked to mutations in genes encoding IF proteins. Yet the properties of IFs are poorly understood, partly because of the lack of powerful genetic model systems, and partly because of the inability to determine their crystal structures. We have shown that IF-like proteins are widely spread in bacteria, and that their biochemical properties and biological functions are very similar to those of animal IF. This makes bacteria attractive as tractable model organisms to study the basic molecular working principles of IF-like cytoskeletons.

We use two bacterial model systems to address the molecular working principles and the biological roles of the coiled coil cytoskeleton.

Caulobacter crescentus has a specific moon crescent-like cell shape. Crescentin forms an IF-like cytoskeletal structure along one lateral side and converts the otherwise straight rod into a crescent-shaped cell. FilP forms an IF-like cytoskeleton in Streptomyces coelicolor hyphae, and is needed for normal growth and morphology. By using atomic force microscopy we could physically probe the living cells, and show that the FilP cytoskeleton confers rigidity to the cells, a function typical for animal IFs, such as skin keratins.
We use biochemical, structural, and cell biological approaches to dissect several aspects the functions of crescentin in Caulobacter crescentus and FilP in Streptomyces coelicolor.

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