Q.31

Which of the following statement(s) is/are CORRECT about Deinococcus radiodurans?

(A) It has a cell wall consisting of several layers, including an outer membrane that lacks

lipid A

(B) Peptidoglycan in its cell wall has ornithine, in place of diaminopimelic acid, in the N

acetyl muramic acid cross-bridges

(C) It is a Gram-negative organism

(D) It can survive an exposure up to 15000 Gy of ionizing radiation

Deinococcus Radiodurans: Correct Statements on Cell Wall and Radiation Resistance

Deinococcus radiodurans, known as the world’s most radiation-resistant bacterium, features a unique multilayered cell wall and exceptional survival mechanisms. Correct options are (A) and (D) based on its established structural and physiological traits.

Cell Wall Structure (Option A)

Deinococcus radiodurans possesses a complex cell wall with multiple layers, including an inner membrane, peptidoglycan, and an outer membrane lacking lipid A, unlike typical Gram-negative bacteria. This structure includes a surface S-layer with protein complexes like the S-layer deinoxanthin-binding complex (SDBC), enhancing protection against radiation and stress. The absence of lipid A contributes to its atypical envelope organization.

Peptidoglycan Composition (Option B)

Peptidoglycan in Deinococcus radiodurans uses ornithine instead of diaminopimelic acid (DAP) in cross-bridges linked to N-acetyl muramic acid, a feature shared with some Gram-positive-like bacteria. However, this statement aligns partially with its cell wall chemistry but requires verification against standard references, as primary sources emphasize overall multilayering over specific amino acid substitutions.

Gram Staining Classification (Option C)

Deinococcus radiodurans stains Gram-positive despite having an outer membrane, due to its thick peptidoglycan layer and lack of typical Gram-negative lipopolysaccharide features. It is not classified as Gram-negative, making this statement incorrect.

Radiation Survival Capacity (Option D)

This bacterium withstands acute doses up to 12,000-15,000 Gy of ionizing radiation with significant viability, far exceeding human lethal doses of about 10 Gy. Mechanisms include genome redundancy, efficient DNA repair, and manganese-based protein protection against oxidative damage.

(B) Ornithine replaces DAP in peptidoglycan	Uncertain/Partial	Ornithine present, but not universally emphasized over DAP variants

(C) Gram-negative organism	No	Stains Gram-positive

(D) Survives 15,000 Gy radiation	Yes	Tolerates extreme doses