TIMMINS, J. | bioRxiv Science

bioRxiv2024

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.

microbiology↗

bioRxiv2023

Stress-induced nucleoid remodeling in Deinococcus radiodurans is associated with major changes in HU abundance and dynamics

Bacteria have developed a wide range of strategies to respond to stress, one of which is the rapid large-scale reorganization of their nucleoid, which is often associated with a major reprogramming of the gene expression profile. Nucleoid associated proteins (NAPs) are believed to be major actors in this process, but the molecular mechanisms underlying stress-induced nucleoid remodeling remain poorly understood. Here, using the radiation resistant bacterium, D. radiodurans, as a model, and advanced fluorescence microscopy approaches, we examined the changes in nucleoid morphology and compaction induced by either entry into stationary phase or exposure to UV-C light, and characterized the associated changes in abundance and dynamics of the major NAP in D. radiodurans, the heat-unstable (HU) protein. While both types of stress induced a similar macroscopic rearrangement of the nucleoid into a more compact structure, HU diffusion was significantly reduced in stationary phase cells, but was instead dramatically increased following exposure to UV-C, suggesting that the underlying mechanisms of remodeling are distinct. Furthermore, a detailed comparison of the cellular response to sublethal and lethal doses of UV-C light revealed that UV-induced nucleoid remodeling involves a rapid nucleoid condensation step associated with increased HU diffusion and abundance, followed by a slower decompaction phase to restore normal nucleoid morphology and HU dynamics, before cell growth and division can resume. Together, these findings shed light on the diversity and complexity of stressed-induced nucleoid remodeling processes in bacteria.

microbiology↗