Cyanobacteria (blue–green bacteria) exhibit which overall Gram-type architecture of the cell wall?

Introduction / Context:
Cyanobacteria are oxygenic photosynthetic prokaryotes. Although their staining can vary, their envelope architecture is classically Gram-negative, which has implications for nutrient transport, susceptibility to antibiotics, and environmental resilience.

Given Data / Assumptions:

• Classify cyanobacterial cell-wall type in the Gram sense.
• Recognize ultrastructure rather than staining alone as the key criterion.

Concept / Approach:
Gram-negative architecture features a thin peptidoglycan layer and an outer membrane containing lipopolysaccharide-like molecules. Cyanobacteria possess this overall architecture, including a periplasmic space, making option “a gram-negative cell wall” correct, even if Gram stain outcomes may be atypical in practice.

Step-by-Step Solution:

Verification / Alternative check:
Electron microscopy and biochemical analyses demonstrate outer membranes and thin peptidoglycan in cyanobacteria, aligning with Gram-negative architecture.

Why Other Options Are Wrong:

• Gram-positive wall: would require a very thick peptidoglycan without an outer membrane.
• Neither/No wall: cyanobacteria clearly have peptidoglycan and an outer membrane.

Common Pitfalls:
Equating Gram staining color strictly with envelope type; some organisms stain irregularly yet have definable architecture.

Final Answer:
a gram-negative cell wall