You're describing an experiment where a microorganism produces a chemical that inhibits the growth of other bacteria. This is a classic example of antibiosis, and the microorganism producing the chemical is likely a bacterium.

Here's why:

* Antibiosis: This is a biological interaction where one organism produces a substance that harms or inhibits the growth of another organism.

* Bacteria: Many bacteria produce chemicals called antibiotics that are effective against other bacteria. This is the basis of many of the antibiotics we use in medicine.

To figure out exactly which microorganism is responsible, you would need more information:

* What type of plate was used? Agar plates are commonly used in microbiology experiments.

* What kind of bacteria was growing on the plate? Different bacteria are susceptible to different antibiotics.

* Where did the organism that produced the chemical come from? Was it a pure culture, or a sample from the environment?

Let me know if you have more details about the experiment, and I can help you identify the microorganism!