Microbial extremophile biology: Why is the bacterium Deinococcus radiodurans able to survive massive exposure to ionizing radiation and DNA-damaging conditions?

Introduction / Context:
Deinococcus radiodurans is famous in microbiology for its extraordinary resistance to ionizing radiation, desiccation, and oxidative stress. Understanding why this organism survives massive DNA damage reveals how cells maintain genomic integrity and why certain repair networks are evolutionarily advantageous.

Given Data / Assumptions:

• The organism can survive doses of radiation that generate extensive double-strand DNA breaks.
• Question asks for the primary reason behind survival, focusing on intrinsic biological capabilities rather than physical shielding.
• Only one option must be chosen as best.

Concept / Approach:

The core explanation centers on exceptional DNA repair capacity and genome maintenance strategies. D. radiodurans rapidly reassembles shattered chromosomes through highly efficient homologous recombination, extended synthesis-dependent strand annealing, and robust protection of proteins against oxidation. Polyploidy (multiple genome copies) helps, but it supports rather than replaces the unique repair systems.

Step-by-Step Solution:

Verification / Alternative check:

If shielding were the main factor, cells lacking these repair systems but with thicker walls would show similar survival—this is not observed. Experimental disruption of repair genes drastically reduces resistance, confirming the mechanistic basis.

Why Other Options Are Wrong:

Thick shell: cell envelopes do not block high-energy radiation effectively.

Radioactive elements in cell wall: biologically implausible and not observed.

Many copies of repair genes: polyploidy helps, but without the unique repair networks survival would still fail; thus this is not the best single reason.

Common Pitfalls:

Confusing cause and contributor—multiple genomes aid repair but are not the fundamental reason; the distinctive repair pathways are.

Final Answer:

Because it has unique DNA repair mechanisms