Population structure of the relapsing fever spirochete Borrelia hermsii as indicated by polymorphism of two multigene families that encode immunogenic outer surface lipoproteins - PubMed (original) (raw)

Population structure of the relapsing fever spirochete Borrelia hermsii as indicated by polymorphism of two multigene families that encode immunogenic outer surface lipoproteins

B J Hinnebusch et al. Infect Immun. 1998 Feb.

Abstract

The tick-borne relapsing fever spirochete Borrelia hermsii evades the mammalian immune system by periodically switching expression among members of two multigene families that encode immunogenic, antigenically distinct outer surface proteins. The type strain, B. hermsii HS1, has at least 40 complete genes and pseudogenes that participate in this multiphasic antigenic variation. Originally termed vmp (for variable major protein) genes, they have been reclassified as vsp (for variable small protein) and vlp (for variable large protein) genes, based on size and amino acid sequence similarities. To date, antigenic variation in B. hermsii has been studied only in the type strain, HS1. Nucleotide sequence comparisons of 23 B. hermsii HS1 genes revealed five distinct groups, the vsp gene family and four subfamilies of vlp genes. We used PCR with family- and subfamily-specific primers, followed by restriction fragment length polymorphism analysis, to compare the vsp and vlp repertoires of HS1 and seven other B. hermsii isolates from Washington, Idaho, and California. This analysis, together with pulsed-field gel electrophoresis genome profiles, revealed that the eight isolates formed three distinct groups, which likely represent clonal lineages. Members of the three groups coexisted in the same geographic area, but they could also be isolated across large geographical distances. This population structure may result from immune selection by the host, as has been proposed for other pathogens with polymorphic antigens.

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Figures

FIG. 1

Map of western United States showing the geographic origins of the eight B. hermsii isolates used in this study. A Roman numeral subscript indicates the group to which an isolate belongs, based on the similarity of the vsp and vlp gene repertoire. C, CON; D, DAH; F, FRO; H, HS1; HN, HAN; M, MAN; R, REN; Y, YOR.

FIG. 2

Dendrograms comparing the genetic relatedness of 9 vsp (A) and 14 vlp (B) gene sequences of B. hermsii HS1. The vlp genes are subdivided into four subfamilies, labelled α to δ. The percentage of nucleotide sequence similarity between genes or gene clusters is indicated at each branchpoint.

FIG. 3

Nucleotide sequence features of vsp and vlp genes of B. hermsii HS1. The central, most variable segment of these genes is flanked by conserved regions (shaded areas for vsp and hatched areas for vlp) that contain the vsp family- or vlp subfamily-specific PCR primer binding sites (arrows). The short 5′ leader sequence shared by genes of both families is indicated by a black box, and asterisks denote stop codons.

FIG. 4

PCR profiles of vsp and vlp genes of relapsing fever Borrelia species. PCRs with primer sets specific for B. hermsii HS1 vlp subfamilies α through δ (A through D, respectively) and vsp family (E) were performed with DNAs isolated from the indicated Borrelia species. PCRs were analyzed on 4% polyacrylamide gels. Lanes 1 through 8, the indicated isolates of B. hermsii; lanes 9 through 11, relapsing fever agents B. turicatae (B. tur.), B. parkeri (B. park.), and B. crocidurae (B. croc.), respectively; lanes 12, B. anserina (B. ans.); lanes 13, B. coriaceae (B. cor.); lanes 14, from B. burgdorferi (B. burg.) B31. Horizontal bars designate the three groups of related B. hermsii isolates. The sizes (in base pairs) of selected _Hae_III-digested φX170 DNA molecular weight standards (mws) are shown on the left.

FIG. 5

vsp gene family RFLP profiles of eight B. hermsii isolates. Gene fragments amplified by PCR with vsp family-specific primers were digested with _Dde_I (A) or _Rsa_I (B) and analyzed on ethidium bromide-stained 3% agarose gels. Lanes 1 through 8, the indicated B. hermsii isolates (horizontal bars designate the three groups of related isolate); lanes mws, _Hae_III-digested φX170 DNA molecular weight standards.

FIG. 6

(A) PFGE gel showing linear-chromosome (lc) and linear-plasmid (lp) profiles of eight B. hermsii isolates (lanes 1 through 8) and high-passage B. burgdorferi (B. burg.) B31 (lane 9). Arrowheads indicate the HS1 expression plasmid. During in vitro passage after isolation, the size of this plasmid increased by about 10 kb. (B) Southern blot (SB) probed with the total collection of PCR-amplified B. hermsii HS1 vsp and vlp gene fragments (vsp + vlp genes). The sizes (in kilobases) of selected lambda DNA concatemers and the 16-kb linear plasmid of B. burgdorferi B31, used as molecular weight standards (mws), are shown on the left. Horizontal bars designate the three groups of related B. hermsii isolates.

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Population structure of the relapsing fever spirochete Borrelia hermsii as indicated by polymorphism of two multigene families that encode immunogenic outer surface lipoproteins - PubMed (original) (raw)