Functional redundancy and stability support the resilience of the Evernia prunastri holobiont under urbanization

Background
Lichens are now recognized as holobionts comprising a mycobiont, photobiont, and diverse microbiomes, yet the functional roles of these additional microbial partners remain poorly characterized, especially under urbanization. Here, we used the epiphytic lichen Evernia prunastri from urban and natural areas to test the hypothesis that its resilience to urbanization is underpinned by functional stability and redundancy within its multi-kingdom consortium.

Results
Using an integrated approach of amplicon and shotgun metagenomic sequencing, we found that the bacterial community structure and the functional potential of the mycobiont, bacteria, and fungi remained stable despite urbanization, highlighting stability and resistance to urban environmental stress. Furthermore, by focusing on symbiosis-related functions, we found that each partner shows tendencies toward certain roles, yet we discovered broad functional overlap, suggesting microbial contributions that buffer the symbiosis. Finally, we found that E. prunastri and its microbiome harbors diverse biosynthetic gene clusters with predicted ecological functions relevant for the symbiosis, spanning photoprotection, oxidative stress mitigation, nutrient acquisition, defense, and chemical communication.

Conclusions
Our study provides unprecedented genomic evidence that lichen resilience is an emergent property of the integrated holobiont, where functional complementarity and redundancy among diverse symbiotic partners maintain stability under urban environmental conditions.