Variable Tick Protein in Two Genomic Groups of the Relapsing Fever Spirochete Borrelia hermsii in Western North America

Abstract

Borrelia hermsii is the primary cause of tick-borne relapsing fever in North America. When its tick vector, Ornithodoros hermsi, acquires these spirochetes from the blood of an infected mammal, the bacteria switch their outer surface from one of many bloodstream variable major proteins (Vmps) to a unique protein, Vtp (Vsp33). Vtp may be critical for successful tick transmission of B. hermsii; however, the gene encoding this protein has been described previously in only one isolate. Here we identified and sequenced the vtp gene in 31 isolates of B. hermsii collected over 40 years from localities throughout much of its known geographic distribution. Seven major Vtp types were found. Little or no sequence variation existed within types, but between them significant variation was observed, similar to the pattern of diversity described for the outer surface protein C (OspC) gene in Lyme disease spirochetes. The pattern of sequence relatedness among the Vtp types was incongruent in two branches compared to two genomic groups identified among the isolates by multilocus sequence typing of the 16S rRNA, flaB, gyrB, and glpQ genes. Therefore, both horizontal transfer and recombination within and between the two genomic groups were responsible for some of the variation observed in the vtp gene. O. hermsi ticks were capable of transmitting spirochetes in the newly identified genomic group. Therefore, given the longevity of the tick vector and persistent infection of spirochetes in ticks, these arthropods rather than mammals may be the likely host where the exchange of spirochetal DNA occurs.

Dual Binding Specificity of a Borrelia hermsii-Associated Complement Regulator-Acquiring Surface Protein for Factor H and Plasminogen Discloses a Putative Virulence Factor of Relapsing Fever Spirochetes

“…However, Hovis and colleagues proposed that although determinants of the C-terminal domain of FhbA are important in FH/FHL-1 binding, the 10-aa Cterminal tail is dispensable (19). In this context the recent identification of two genetically distinct groups of B. hermsii is of interest (56). Together with the proposition of two clusters of FH binding proteins found in the B. hermsii genome, the combined studies thus suggest a differential association of FhbA and BhCRASP-1 with the two subgroups (57).…”

Large Linear Plasmids of Borrelia Species That Cause Relapsing Fever

“…B. hermsii strain HS1 serotypes 7 and 33 (31) and strain DAH (32) from eastern Washington, B. turicatae strain 91E135 (also known as "Oz1") from western Texas (33,34), and B. parkeri strain HR1 from northern California were used. Isolates HS1 and DAH are the same strain on the basis of restriction fragment length polymorphism analysis and multilocus sequence typing (35,36). Their ϳ950-kb-long chromosomes are Ͼ99.99% identical in sequence (A. G. Barbour, unpublished data).…”

Borrelia burgdorferi OspC Protein Required Exclusively in a Crucial Early Stage of Mammalian Infection

“…The related spirochete Borrelia hermsii has a gene homologous to ospC, called vtp, whose product is also present on the bacterial surface during transmission from tick to mammal (7,42). Surprisingly, although the predicted OspC and Vtp products are only about 50% identical, the signal sequences are invariant (28,36), raising the intriguing possibility that the cleaved signal sequences may have additional roles, perhaps as peptide pheromones.…”