Comparative analysis of Borrelia’s Defence mechanisms and their impact on genetic manipulation of low-passage isolates of Borrelia afzelii and Borrelia garinii – Research

Borrelia, a highly prevalent tick-borne pathogen, has a genome with a linear chromosome and numerous linear and circular plasmids. There are three groups of Borrelia: Lyme borreliosis, relapsing fever, and Echidna-reptile. In Europe, Borrelia afzelii and Borrelia garinii are the main causative agents of Lyme borreliosis. The primary defence mechanism of bacteria against bacteriophages and other invading DNA elements is the restriction-modification system (RMS), which discriminates between native and foreign DNA based on their distinct methylation patterns. This present study compares the RMS of all the Borrelia species available in the REBASE database. Additionally, it investigates the effect of the RMS on the transformation efficiency of low-passage B. afzelii and B. garinii isolates. Upon comparing the RMS of 18 Borrelia species, differences in the number, location and characteristics of genes were observed between groups. Given that Lyme borreliosis species exhibit higher genomic plasticity, we hypothesise that they possess a greater number of RMS genes to ensure functionality of the RMS even if some plasmids are lost. In this study, we demonstrate a large increase in transformation efficiency of low-passage strains by using an in vitro methylated shuttle vector, confirming our hypothesis that the RMS of Borrelia recognises pre-methylated vectors as native DNA. The knowledge gained in this study contributes to the understanding of Borrelia defence mechanisms and provides possible explanations for the relatively low transformation efficiency observed in previous studies. Consequently, in vitro methylation can serve as a valuable tool for facilitating studies involving genetic manipulation of Borrelia.