Researchers discovered that fungal endophytes living inside perennial ryegrass plants host communities of bacteria, primarily from the Paenibacillus genus. Two specific bacterial strains were isolated and found to interact antagonistically, with one strain acting as a ‘keystone’ species that controls the composition of the entire bacterial community. Despite these complex bacterial interactions, the bacteria did not negatively affect the fungal endophyte’s growth, suggesting a balanced symbiotic relationship beneficial to the grass plant.