Combining live cell fluorescence imaging with in situ cryo electron tomography sheds light on the septation process in Deinococcus radiodurans

Cell division is a fundamental biological process that allows a single mother cell to produce two daughter cells. In bacteria, different modes of cell division have been reported that are notably associated with distinctive cell shapes, but in all cases, division involves a step of septation, corresponding to the growth of a new dividing cell wall, followed by splitting of the two daughter cells. The radiation-resistant Deinococcus radiodurans is a spherical bacterium protected by a thick and unusual cell envelope. It has been reported to divide using a distinctive mode of septation in which two septa originating from opposite sides of the cell progress with a flat leading edge until meeting and fusing at mid-cell. In the present study, we have combined conventional and super-resolution fluorescence microscopy of live bacteria with in situ cryogenic electron tomography of bacterial lamellae to investigate the septation process in D. radiodurans. This work provides important insight into (i) the complex architecture of the cell envelope of this bacterium, (ii) the sliding doors septation process and (iii) the molecular mechanisms underlying septal growth and closure.