Giant sulfur bacterium — Thiomargarita namibiensis: Which statements are true about this organism often called the “sulfur pearl of Namibia”?

Introduction / Context:
Thiomargarita namibiensis exemplifies extreme prokaryotic cell size and unusual physiology. Knowing its traits illustrates how bacteria can adapt to fluctuating redox conditions in sediments.

Given Data / Assumptions:

• Size claim (largest known bacterium) must be recognized.
• Presence of a massive nitrate-storing vacuole (~98% volume).
• Evaluate which statements are true.

Concept / Approach:
This sulfur-oxidizing Gammaproteobacterium forms large spherical cells visible to the naked eye. The enormous central vacuole accumulates nitrate, used as an electron acceptor when environmental oxygen is scarce, enabling chemosynthesis with reduced sulfur compounds.

Step-by-Step Solution:
Confirm extraordinary size: hundreds of micrometers in diameter. Confirm vacuole function and approximate 98% volume occupancy. Reject “smallest” claim; accept both (a) and (b).

Verification / Alternative check:
Field and microscopy studies from Namibian shelf sediments document giant cells and nitrate-storing vacuoles supporting anaerobic metabolism.

Why Other Options Are Wrong:

• Only one of the statements: incomplete.
• Smallest bacterium: the opposite of its defining trait.

Common Pitfalls:
Assuming all bacteria are microscopic; exceptions like Thiomargarita and Epulopiscium challenge that notion.

Final Answer:
Both (a) and (b)