Extremophile microbiology – Deinococcus hallmark: Deinococci (Gram-positive cocci/rods with unusual envelopes) are distinctive for their exceptional resistance to which stresses?

Introduction / Context:
Deinococcus species are model organisms for studying DNA repair and stress tolerance. Their fame comes from surviving astonishing doses of ionizing radiation and severe drying, making them relevant to biotechnology and astrobiology discussions.

Given Data / Assumptions:

• Deinococci show polyploid genomes and robust DNA repair systems.
• Pigmented carotenoids and protective proteins mitigate oxidative damage.
• Desiccation and radiation cause similar DNA lesions (e.g., double-strand breaks).

Concept / Approach:
Resistance to radiation and desiccation derives from efficient DNA repair (extended synthesis-dependent strand annealing and other pathways), protein protection from reactive oxygen species, and cellular compartmentalization. Temperature extremes are not their primary hallmark across the genus, although some tolerance exists.

Step-by-Step Solution:
Identify signature stresses: ionizing radiation and drying. Explain mechanistic overlap in damage and repair between the two stresses. Select the combined option reflecting both characteristics.

Verification / Alternative check:
Experimental data show survival after thousands of grays of radiation and prolonged desiccation with rapid recovery on rehydration.

Why Other Options Are Wrong:
Choosing only one stress is incomplete; exclusive temperature or salinity focus misses the defining trait of the group.

Common Pitfalls:
Assuming Gram reaction predicts envelope properties; deinococci have atypical envelopes that behave differently from classic Gram-positives.

Final Answer:
Both (a) and (b).