An ecological corridor reveals new Liberibacter taxa along a latitudinal transect of Salix and Urtica

Abstract Liberibacter species range from facultative insect symbionts to devastating plant pathogens, yet their diversity, transmission routes, and ecological roles remain poorly understood. We screened willow-associated psyllids along a latitudinal transect spanning Europe with complementary sampling in North America to examine Liberibacter diversity and potential mechanisms of horizontal transmission within an eco-evolutionary framework. Through 16S rRNA amplicon profiling, targeted metagenomics, and whole genome phylogenomics, we identified and sequenced a new ‘ Candidatus Liberibacter psyllidaureus’ haplotype ( W ) and describe a new species, ‘ Candidatus Liberibacter saliceti’. Single-gene markers suggest the potential for horizontal transmission of Liberibacter genotypes among co-occurring psyllid species within shared riparian habitats. Comparative genomic analyses reveal that virtually all Liberibacter species encode arginine and B-vitamin biosynthesis pathways absent or incomplete in psyllid obligate nutritional symbionts, suggesting a putative facultative nutritional role. Together, our results highlight riparian ecosystems as hotspots of Liberibacter diversity, transmission, and functional integration within complex psyllid symbiotic consortia.