How would you recognize an antibiotic-producing soil bacterium on a plate crowded with other bacteria? the bacterial colony producing the antibiotic would be

Alone, with a ring surround it with any bacterial growth.

Explanation:

Since the colony produce an antibiotic, but at the same time is a waste of this colony. Is not going to kill them but is able to kill the bacteria that surrounds this colony. It will look a little bit strange because after the antibiotic ring it will be a millions of cells.

your answer is going to be physical weathering