Vitronectin binding protein, BOM1093, confers serum resistance on Borrelia miyamotoi

Kozue Sato,Gaowa Gaowa,Makoto Kuroda,Hiroki Kawabata,Tetsuya Hayashi,Makoto Ohnishi,Ai Takano,Kyle R Taylor,Tsuyoshi Sekizuka,Yumi Kumagai

doi:10.1038/s41598-021-85069-w

Abstract

Borrelia miyamotoi, a member of the tick-borne relapsing fever spirochetes, shows a serum-resistant phenotype in vitro. This ability of B. miyamotoi may contribute to bacterial evasion of the host innate immune system. To investigate the molecular mechanism of serum-resistance, we constructed a membrane protein-encoding gene library of B. miyamotoi using Borrelia garinii strain HT59G, which shows a transformable and serum-susceptible phenotype. By screening the library, we found that bom1093 and bom1515 of B. miyamotoi provided a serum-resistant phenotype to the recipient B. garinii. These B. miyamotoi genes are predicted to encode P35-like antigen genes and are conserved among relapsing fever borreliae. Functional analysis revealed that BOM1093 bound to serum vitronectin and that the C-terminal region of BOM1093 was involved in the vitronectin-binding property. Importantly, the B. garinii transformant was not serum-resistant when the C terminus-truncated BOM1093 was expressed. We also observed that the depletion of vitronectin from human serum enhances the bactericidal activity of BOM1093 expressing B. garinii, and the survival rate of BOM1093 expressing B. garinii in vitronectin-depleted serum is enhanced by the addition of purified vitronectin. Our data suggests that B. miyamotoi utilize BOM1093-mediated binding to vitronectin as a mechanism of serum resistance.

Highlights

Borrelia miyamotoi was first discovered in Hokkaido, Japan in 1 9951
17 Borrelia strains of B. garinii and B. bavariensis were examined for serum-sensitivity by determining the survival rate following treatment with 40% Normal human serum (NHS) or Heat-inactivated human serum (HIS) for 16 h (Figure 1)
To investigate the transformability of these B. garinii strains, the shuttle vector pBSV2 was electroporated into each serum-susceptible B. garinii strain

Summary

Introduction

Borrelia miyamotoi was first discovered in Hokkaido, Japan in 1 9951. B. miyamotoi is classified to relapsing fever (RF) borreliae, it was discovered in the hard-bodied tick, Ixodes persulcatus[1]. The first cases of B. miyamotoi infection in humans were reported in Russia and were referred to as “Emerging RF”7. The mechanisms utilized by the BMD pathogen, B. miyamotoi, are not fully understood Genetic approaches such as mutagenesis and complementation have been employed to study genes of genus Borrelia over the last few decades, these processes have not been established for B. miyamotoi. We employed a similar surrogate system by first establishing a transformable/serum susceptible Borrelia strain to use in our investigation. Using this strain, we attempted to comprehensively screen genes involved in serum resistance of B. miyamotoi and found that a vitronectin (Vn)-binding protein contributed to serum resistance of B. miyamotoi in vitro. Our data suggests B. miyamotoi may utilize Vn-binding to evade the complement system in human serum

Methods

Results

Conclusion