https://phys.org/news/2018-07-antibiotic-weeds.html

This microcosm, known as the phyllosphere, is poor in nutrients. "That gives rise to intense competitive pressure," says Julia Vorholt. "As a result, bacteria produce a diversity of substances that allow them to defend their habitat." That's because despite the scarce food supply, the phyllosphere is populated by a large number of organisms. Vorholt and Piel investigated more than 200 bacterial strains that occur in the widespread thale cresses.

Diverse antibiotic effects among bacteria