A team from CEA-IRIG, among the few researchers studying Deinococcus radiodurans, has used advanced fluorescence microscopy techniques to reveal, for the first time, the process of nucleoid remodeling in this bacterium. This remodeling is crucial for its exceptional resistance to extreme conditions such as ionizing and UV radiation and prolonged drought. This discovery adds to our understanding of the survival mechanisms of this unique bacterium.

Nucleoid remodeling is a common strategy used by bacteria to protect their DNA in response to external stress. This process is mainly controlled by nucleoid-associated proteins (NAPs), which interact with DNA to compact the genome. This compaction helps to maintain the integrity of the genetic material under adverse conditions.

In previous studies, researchers from this team have shown that the D. radiodurans nucleoid is compact, yet sufficiently dynamic to adapt to the morphology of the cell during the cell cycle. This new study now examines the impact of two stresses on the morphology and state of compaction of the nucleoid: exposure to UV-C radiation, which damages the genome, and nutrient deprivation which leads to stationary phase and growth arrest. The study also assesses how these stresses affect the mobility of the HU protein, the main NAP in these nucleoids, in order to probe its interaction with the DNA.

The study shows that nutrient and UV-C stress cause rapid nucleoid compaction, but by distinct mechanisms. HU mobility decreases in response to nutrient deprivation, whereas it increases in response to UV-C light. After a phase of rapid condensation due to UV-C, the nucleoid slowly decompacts, allowing HU to regain its normal mobility and the nucleoid to return to its initial structure, before recovery of cell growth.

For the first time, this study has allowed the visualization in real time of the nucleoid remodeling process in D. radiodurans using advanced fluorescence microscopy techniques. This direct observation has contributed to a better understanding of the resistance mechanisms of this exceptional bacterium.