A team of researchers has studied
Deinococcus radiodurans and revealed for the first time the process of nucleoid remodeling in this bacterium, using advanced fluorescence microscopy techniques.
This remodeling is crucial for its exceptional resistance to extreme conditions such as ionizing and UV radiation, as well as prolonged dryness. This discovery enhances our understanding of the survival mechanisms of this unique bacterium.
Nucleoid remodeling is a common strategy among bacteria to protect their DNA against external stresses. This process is primarily controlled by NAPs (Nucleoid Associated Proteins), which interact with the DNA to compact the genome. This compaction helps preserve the integrity of genetic material under unfavorable conditions.
In previous studies, the researchers of this team showed that the nucleoid of
D. radiodurans was compact yet dynamic, allowing it to adapt to the morphology of the cell during its cell cycle.
This new study examines the impact of two stress factors on the morphology and compaction state of the nucleoid: exposure to UV-C rays that damage the genome, and a nutritional deficiency leading to a stationary phase that limits growth. The study also evaluates how these stresses affect the mobility of the HU protein, the main NAP of the nucleoid, in order to assess how it interacts with the DNA.
The study shows that nutritional and UV-C stress trigger rapid nucleoid compaction, though through different mechanisms. HU mobility decreases in response to nutritional deficiency, while it increases under UV-C exposure. 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, ready for the resumption of cellular growth.
Microscope photo. On the right, nucleoid markings in green and membrane in red:
(1) Normal nucleoids.
(2) Compact nucleoids due to nutritional deficiency.
(3) Compact nucleoids after UV-C irradiation.
© CEA
This research enabled, for the first time, the real-time observation of nucleoid remodeling in
D. radiodurans, through advanced fluorescence microscopy techniques. This direct observation enhances our understanding of the resistance mechanisms of this remarkable bacterium.
References:
Vauclare P, Wulffelé J, Lacroix F, Servant P, Confalonieri F, Kleman JP, Bourgeois D and Timmins J.
Stress-induced nucleoid remodeling in
Deinococcus radiodurans is associated with major changes in Heat Unstable (HU) protein dynamics.
Nucleic Acids Res 2024.