Dr Sofia Magkiriadou
Université de Fribourg, Soft Matter and Optics Group
work performed at the Ecole Polytechnique Fédérale de Lausanne, Laboratory for Experimental Biophysics)

“Polyphosphate affects dynamics in the cytoplasm of starved P.aeruginosa”

The bacterial cytoplasm is a complex medium out of equilibrium, whose properties can change depending on the state of the cell. Bacteria are often under stress, both in the environment, for instance due to lack of nutrients, as well as in the context of disease, for instance because of antibiotic treatment. Therefore, it is especially important to understand the cellular state under hostile conditions.
Here we study the cytoplasm of an opportunistic pathogen, P. aeruginosa, in the context of nitrogen starvation. In particular, we investigate the role of a ubiquitous biological macromolecule that is important for bacterial stress response: polyphosphate. To probe the cellular interior, we use fluorescence microscopy and particle tracking, and we characterize the motion of chromosomal loci and of passive tracer particles.
Our observations show that in starving mutant cells without polyphosphate, motion becomes more diffusive. Moreover, tracer particles of different sizes reveal that polyphosphate affects motion in a size-dependent way: while the smallest particles can diffuse under all conditions, in starved cells larger particles can only diffuse in the absence of polyphosphate. Our findings suggest that polyphosphate may play an important role in the regulation of the physical properties of the cytoplasm during starvation via various mechanisms, which I will discuss. Further understanding these mechanisms can shed light on bacterial stress response, and thus inspire novel antibiotic approaches.