Pan-genome classification of the virulence spectrum of Bartonella and the variation of heme-binding protein virulence factor in isolates from the Tibetan Plateau.

This study classifies Bartonella species based on virulence factors and explores the genomic characteristics of Bartonella isolates from the Qinghai-Tibet Plateau to understand their ecological adaptations. PCR detection and isolation culture of Bartonella were performed on 50 captured pikas in their habitats on the Qinghai-Tibet Plateau. The Qinghai-Tibet isolates were identified through gltA and rpoB phylogenetic analysis, ANI analysis, and single-copy homologous gene phylogeny. Reference genomes of Bartonella species were analyzed for virulence classification via pan-genome and virulence factor comparisons. Bartonella species were categorized into five virulence groups, including a high-virulence group containing Bartonella henselae, B. quintana, B. kosoyi, B. koehlerae, and B. tribocorum. B. bacilliformis lacked Trw and VirB/VirD4, while the copy number of flagella was significantly higher. Bartonella grahamii infected up to 12% of plateau pikas from the Qinghai-Tibet Plateau. B. grahamii plateau isolate had the most unique genes (5.6%), with 65.06% of them unknown in function, followed by replication, recombination, and repair (11.64%), and amino acid transport and metabolism (5.48%). The heme-binding protein virulence factor in B. grahamii plateau isolate exhibited 14 amino acid mutations, leading to changes in the protein-binding sites. Bartonella can be classified into five virulence groups. In the high-virulence group, the less common B. tribocorum and B. kosoyi are included. Trw and VirB/VirD4 gradually replaced ancestral flagella genes in Bartonella evolution. The isolated strains have more unique genes due to plateau pikas' unique physiological traits, which may be connected to adaptation to the high-altitude host environment. IMPORTANCE Bartonella species are emerging zoonotic pathogens capable of infecting a wide range of mammals, including humans. Understanding their virulence and evolution is critical for assessing potential public health risks. This study classifies Bartonella species based on virulence factors, revealing species with potential human pathogenicity. The Qinghai-Tibet Plateau, with its extreme environment, may drive bacterial adaptation. By analyzing Bartonella isolates from plateau pikas, we identified unique genes and virulence factor variations, providing insights into bacterial evolution in high-altitude hosts. Our findings highlight the significance of pan-genome analysis in identifying pathogenic traits and evaluating zoonotic risks. This study enhances our understanding of Bartonella adaptation, aiding in the clinical identification and characterization of highly pathogenic strains.