Candidatus Liberibacter sp. is detected in Russelliana solanicola Tuthill (Hemiptera: Psyllidae) in Brazil: phylogenetic and functional insights

Emerging diseases associated with Candidatus Liberibacter have become increasingly significant in recent decades. Devastating diseases such as Zebra Chip and Huanglongbing, caused by Ca. L. solanacearum (CLsol) and Ca. L. asiaticus (CLas), respectively, are leading to substantial economic losses in agriculture worldwide. Ca. Liberibacter is a phloem-restricted bacterial genus that, as far as currently known, is naturally transmitted exclusively by psyllids (Hemiptera: Psylloidea). The South American potato psyllid Russelliana solanicola Tuthill (Psyllidae), recognized as a potential vector of Ca. Liberibacter, feeds on a diverse range of plants from families such as Solanaceae, Apiaceae, and Asteraceae, including both cultivated and non-cultivated species. The hybrid approach, integrating metagenomic and metataxonomic methods, enabled the discovery of a novel association between Ca. Liberibacter sp. and R. solanicola. This was achieved through shotgun sequencing utilizing Illumina technology and amplicon sequencing with Oxford Nanopore Technology. Subsequent phylogenetic, genomic, and functional analyses enabled a comprehensive initial characterization of the bacterium. Phylogenetic analysis of 16S rRNA gene sequences revealed that Ca. Liberibacter sp. associated with R. solanicola forms a distinct clade closely related to Ca. L. americanus and Ca. L. europaeus, sharing 98% sequence identity. This clade diverges from other species, including CLsol, CLas, and C. L. africanus. Metagenomic analysis recovered 81 contigs with high assembly consistency (90.1% coarse, 89.6% fine) and an N50 value of 168,363 bp. Functional annotation identified 205 protein-encoding genes with assigned functions and 176 protein-encoding genes without functional assignments, highlighting both known and unexplored aspects of its genomic repertoire. The phylogenetic relationships, combined with the identified genomic and functional characteristics, open the door to understanding the potential ecological role of this association and future implications, especially considering the polyphagy of R. solanicola. This research is ongoing and remains crucial for understanding its role in uncovering novel bacterial species and ecological associations.