Genetic Characterisation of the Bacterial Microbiota Associating With a Strain of Epichloë Fungal Endophyte of Perennial Ryegrass and the Interaction With Its Paenibacillus Members

Summary

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.

Background

Plant-associated fungi can host unique bacterial microbiota that provide multiple benefits to their fungal hosts. Epichloë fungal endophytes form intimate associations with bacteria and co-evolve with cool-season grasses, particularly perennial ryegrass. Few studies have identified keystone taxa within bacterial microbiota of plant-associated fungi.

Objective

To genetically characterise the bacterial microbiota associated with Epichloë fungal endophyte strain AR135 isolated from perennial ryegrass via 16S rRNA gene sequencing and direct microbial isolation, and to investigate microbe-microbe interactions between isolated bacteria and the fungal endophyte.

Results

The bacterial microbiota of AR135 was dominated by Paenibacillus genus (99% abundance), with Delftia and Bradyrhizobium also present. Two Paenibacillus strains (E100 and E300) were isolated and showed antagonistic interaction with E300 reducing E100 abundance by 63-100%. Paenibacillus cells were located on hyphal surfaces both in vitro and in planta, with E300 appearing to be a keystone taxon regulating community structure.

Conclusion

Epichloë fungal endophytes host bacterial communities whose structure is regulated by keystone taxa within the Paenibacillus genus. The antagonistic relationship between E100 and E300 demonstrates that bacterial community composition is dynamically regulated. Bacterial microbiota did not affect fungal biomass under tested conditions, suggesting a neutral to beneficial relationship with the endophyte.
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