Whole Genome Characterization of <i>Borrelia bavariensis</i> Strain KW3 Isolated from <i>Ixodes Granulatus</i> in South Korea

<b><i>Introduction:</i></b> <i>Borrelia bavariensis</i>, a causative agent of Lyme disease, was first reported in South Korea in 2018, yet no complete genome sequence has been described. Here, we present the first whole-genome characterization of <i>B. bavariensis</i> strain KW3, isolated from <i>Ixodes granulatus</i> in the Kangwon region of South Korea. <b><i>Methods:</i></b> Genome assembly was achieved using a hybrid approach combining PacBio and Illumina sequencing. <b><i>Results:</i></b> The KW3 genome consists of a linear chromosome and 12 plasmids, totaling 1.33 Mbp comprising 1,310 annotated genes. Comparative analyses revealed that strain KW3 is most closely related to Japanese strains NT24 and JAASAAF1029. In multiple phylogenetic trees, strain KW3 consistently clustered within the Japanese clade but formed a distinct subbranch, suggesting regional diversification. Several plasmids showed evidence of fusion or divergence, including lp32-10_lp28-4, lp32-10_lp36, and cp32-6_cp32-12, which displayed partial similarity to plasmids of European <i>Borrelia garinii</i> strains PBes (Germany) and 20047 (France). Key plasmid-borne virulence genes (<i>ospA, ospB, ospC, dbpA, dbpB</i>) were fully conserved in strain KW3 and closely matched those of Japanese strains. In contrast, the <i>vlsE</i> locus, typically located on lp28-8 in <i>B. bavariensis</i>, was absent, possibly due to plasmid loss during <i>in vitro</i> culture. <b><i>Conclusions:</i></b> This study provides the first complete genome sequence of <i>B. bavariensis</i> isolate from South Korea and highlights its close relationship to Japanese isolates while revealing unique plasmid features and virulence gene profiles. These findings underscore the importance of continued genomic surveillance to monitor the circulation, evolution, and pathogenic potential of this tick-borne pathogen across East Asia.