**Core Concept:**
The question is asking about the identification of an organism based on its ability to grow on agar plates and produce green colonies. Agar plates are a culture medium used for growing microorganisms, and the presence of green colonies indicates the growth of a specific type of organism.

**Why the Correct Answer is Right:**
The correct answer is **D. Bacillus subtilis**. This bacterium is known to grow on agar plates and produce green colonies due to the presence of a pigment called bacilligenous pigment or green mannitol salt agar pigment. This pigment is produced by the bacterium during its growth and is responsible for the green color of the colonies.

**Why Each Wrong Option is Incorrect:**
A. **Bacillus anthracis**: This bacterium is also known to grow on agar plates, but it produces black colonies due to the presence of a different pigment called anthracin. It is not responsible for green colonies.
B. **Staphylococcus aureus**: Staphylococcus aureus can grow on agar plates, but it does not produce green colonies. It typically forms yellow, creamy, or white colonies.
C. **Pseudomonas aeruginosa**: Pseudomonas aeruginosa can grow on agar plates, but it does not produce green colonies. It typically forms green, blue-green, yellow, or white colonies, depending on the specific growth conditions.

**Clinical Pearl / High-Yield Fact:**
Bacillus subtilis is a common commensal bacterium found in soil, dust, and food. It is not pathogenic but can cause infections in immunocompromised individuals or in specific clinical scenarios like cystic fibrosis. B. subtilis has also been used in the biotechnology industry for various applications, including the production of antibiotics, enzymes, and other bioactive compounds.

**Correct Answer:** D. Bacillus subtilis.