The figure below illustrates one type of bacterial secretion system. Which system is illustrated?

• A. Type VI secretion system
• B. Type III secretion system
• C. Type IV secretion system
• D. Type I secretion system

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the context of bacterial secretion systems, which are specialized protein complexes used by bacteria to transport molecules, such as proteins or DNA, across their cell membranes into the environment or directly into host cells.
2. Step 2: Review the key characteristics of each secretion system type: Type I is a simple one-step system, Type III resembles a syringe-like structure used to inject proteins into host cells, Type IV can transfer DNA and proteins, and Type VI is a contractile system similar to a phage tail.
3. Step 3: Analyze the figure carefully, focusing on structural features such as the presence of a needle-like apparatus, which is characteristic of the Type III secretion system, often described as a molecular syringe.
4. Step 4: Compare the observed features in the figure with the known descriptions of each secretion system to identify which system matches the illustrated structure.
5. Step 5: Conclude that the system illustrated is the Type III secretion system based on the presence of the needle-like injection apparatus and its role in directly injecting effector proteins into host cells.