Molecule diffusion in bacteria and consequences of osmotic stress

PhD ceremony: Mr. J.T. Mika, 12.45 uur, Aula Academiegebouw, Broerstraat 5, Groningen

Dissertation: Molecule diffusion in bacteria and consequences of osmotic stress

Promotor(s): prof. B. Poolman

Faculty: Mathematics and Natural Sciences

The interior of a cell is full of different kinds of (macro)molecules, the crowding of which resembles a shopping mall just a few days before Christmas. The aim of the work of Jacek Mika was to understand how fast molecules move in such an environment. He has presented measurements on the mobility of small, medium and large molecules in the cytoplasm of E. coli. As a tool of manipulating the crowding of cells, he has exposed them to osmotic shifts. When the salt content of the external environment increases, bacterial cells, just like plant cells that have not been watered for a long time, lose water. This results in an increased crowding and a slowing down of the molecule mobility inside cells. An important outcome of the experiments presented in his thesis is that crowding and osmotic stress have more impact on macromolecules than on metabolites. In fact, severe osmotic stress ‘freezes’ proteins as they essentially become immobile. By using a special flow chamber, he has followed the fate of single E.coli cells as they experience osmotic stress. Due to their small size, bacterial cells are difficult to study with light (fluorescence) microscopy. Mika has implemented a new and exciting technique called PALM to perform microscopy of bacteria at increased resolution. This approach allows distinguishing details of structures inside cells that are as small as 10 nm, which is a great improvement as compared to the 250 nm that is the diffraction limit of conventional light microscopy.