P-298 - Pseudomonas in the A. thaliana phyllosphere: the genomic diversity of 5000 wild isolates

The Pseudomonas syringae species complex includes over 60 pathovars and some of the most economically devastating bacterial plant pathogens. Wild populations of Pseudomonas are acutely relevant for agriculture as they serve as potential sources for emerging crop-pandemic strains, but remain under-studied due to historical focus on the latter. We present a collection of 5000 Pseudomonas isolates sampled from the phyllosphere of wild-growing Arabidopsis thaliana plants across 291 sites spanning Europe and parts of Asia. Using whole-genome assemblies, we analyse the population structure and identify over 1200 distinct strains, including those with high similarity to agriculturally relevant strains such as Pss9644, PtoDC3000 and Psa NZ V-13. While geographically distant sites show evidence of genetic linkage, there is also considerable diversity both between sites and within the same host. Many of these endophytic isolates match those previously sampled from soil or diseased animal hosts, showing the overlap in ecological niches between divergent lineages. Finally, we delve into the pan-genomic content, characterise the core genome and the variation in effectors, pathogenicity islands, copper resistance genes and prophages, and assess the impact of geographic variables. This collection of live cultures with WGS data sheds light on Pseudomonas population dynamics and provides a vast resource with potential applications in genome mining and identification of new biocontrol agents.