Which of the following statements is NOT true for Pelagibacter?

• A. It has a very small genome compared to most bacteria.
• B. It is a Gram-positive bacterium.
• C. It is one of the most abundant microorganisms in the ocean.
• D. It plays a significant role in the global carbon cycle.

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the characteristics of Pelagibacter. Pelagibacter is known as one of the most abundant marine bacteria and has a very small genome compared to most bacteria.
2. Step 2: Recall the Gram stain classification. Pelagibacter is classified as a Gram-negative bacterium, meaning it does not retain the crystal violet stain used in Gram staining and instead appears pink/red after counterstaining.
3. Step 3: Analyze each statement in the problem: (a) It has a very small genome compared to most bacteria — this is true. (b) It is a Gram-positive bacterium — this is likely false because Pelagibacter is Gram-negative. (c) It is one of the most abundant microorganisms in the ocean — this is true. (d) It plays a significant role in the global carbon cycle — this is true.
4. Step 4: Identify the statement that is NOT true. Since Pelagibacter is Gram-negative, the statement claiming it is Gram-positive is incorrect.
5. Step 5: Conclude that the correct answer to the problem is the statement 'It is a Gram-positive bacterium' because it contradicts the known microbiological classification of Pelagibacter.