One of the aims of this PhD project is to contribute to a better understanding of the cell morphology and the nucleoid organization/segregation in cocci. For that matter, we explored the 4D organization and the dynamics of D. radiodurans nucleoids, as a function of the cell cycle progression and growth phase. Several strategies were undertaken : (i) timelapse 3D stacks by spinning confocal microscopy (ii) dynamics studies with FRAP analysis and SptPALM acquisitions, and (iii) cartographies of nucleoid associated proteins using super-resolution microscopy (PALM). We were thus able to show that the multiple copies of the 4 replicons that possess D. radiodurans are grouped into a single nucleoid, which adopts distinct shapes throughout the cell cycle : a toroid shape in new-born cell, a square shape or a crescent shape in the next phases of the cycle, a rod shape at the beginning of septation, a branched shape during later stage of septation and a double ring shape at the end of cytokinesis. These observations will be the basis of future works on the dynamics of DNA repair machineries and also bring new perspective on DNA organization and segregation in cocci.

Contact : ibs.seminaires@ibs.fr