The 44‐kb Linear Plasmid Molecule in the Relapsing Fever Agent Borrelia duttonii Strain Ly Serve as a Preservation of vmp Genes

Abstract

Relapsing fever is a disease caused by a spirochete that belongs to the genus Borrelia. The borreliae are transmitted from one vertebrate host to another by the bite of Ornithodoros ticks (Argasidae) or louse, Pediculus humanus (5). These organisms are divided into two groups old-world and new-world relapsing fever borreliae based on their distribution areas. Borrelia hermsii (one of the new-world group) causes an illness characterized by periods of fever and spirochetemia, separated by febrile intervals without evidence of the organism in the blood (3,6). This phenomenon has been described to confer the ability to avoid host immune response, and is a multiphasic antigenic variation of surfaceexposed outer membrane lipoprotein. In contrast, Borrelia crocidurae (one of the old-world relapsing fever Borrelia) shows different behavior from that of B. hermsii. During infection in mice, prolonged spirochetemia results in an erythrocyte rosette formation (7). However, both Borrelia species display antigenic variation that allows it to escape host immune response. This mechanism has been extensively studied, and several vmp genes have been identified and have been divided into two families: vlp (variable large protein of average molecular weight, 33 36 kDa) and vsp (variable small protein, approximate molecular weight of 22 kDa) genes, on the basis of their molecular sizes (8,20).The genome of both relapsing fever and Lyme disease borreliae is composed of one linear chromosome of about one megabase and several linear and circular plasmid molecules (2,4,21,26). Some of these plasmids carry genes for variable major protein (Vmp) in relapsing fever borreliae and the outer surface membrane protein (Osp) in Lyme disease spirochetes (3, 9). Several studies have recently shown that the absence of certain plasmid molecules in the borrelial cell correlates with loss of infectivity in mice (24, 29). In our previous work, the size conversion of the 44-kb plasmid in B. duttonii strain Ly caused a loss of infectivity in mice, and it was possible that gene(s) on the 44-kb plasmid molecule are important in the spirochete's escape from the host defense mechanism. It is of interest to identify the gene(s) essential for spirochete infection in mice. We therefore attempted to identify the whole nucleotide sequence

New World Relapsing Fever Borrelia Found in Ornithodoros porcinus Ticks in Central Tanzania

“…A different set of conditions (40 s at 94 C, 30 s at 67 C, 90 s at 72 C, 35 cycles) was used for borrelial rrs amplification. Sequences of both flaB and rrs PCR products were determined directly in both directions by using custom-synthesized sequencing primers and a BigDye terminator cycle sequencing FS ready reaction kit (Applied Biosystems) as described previously (10,19).…”

Immunodominant Epitope in the C‐Terminus of a Variable Major Protein in Borrelia duttonii, an Agent of Tick‐Borne Relapsing Fever

“…B. duttonii strain Ly was isolated from a 2-year-old girl with TBRF in Tanzania (9) and used for all experimental work in this study. It has been passed in broth medium continuously at least 5 times, and stored at Ϫ80 C. B. duttonii strain Ly was grown in Barbour-Stoenner-Kelly's (BSK) II medium supplemented with 6% rabbit serum at 32 C as described previously (40).…”

“…A: The primary amino acid sequence of VmpP is cited from DDBJ/EMBL/GenBank database (accession no. AB073701) (40). Amino acid number is indicated below the sequence, and putative signal sequence and VmpP-S34 regions are also shown.…”

“…Results are 296 N. TABUCHI ET AL Nucleotide sequence accession numbers. The VmpP, VmpG, VmpL, and VmpK sequences of the B. duttonii strain Ly have been assigned DDBJ/EMBL/GenBank accession number AB073701 (40). The accession numbers of B. hermsii Vmp sequences published previously (6, 34) are as follows: Vmp7, X53926; Vmp18, U52149; Vmp21, M57256; Vmp25, L04787.…”

“…The size change of linear plasmid from 44 to 69-kb during in vitro cultivation of this strain caused loss of infectivity in experimental mice, leading us to believe that genes on this plasmid may be involved with infectivity in mammals. Therefore, we determined the entire nucleotide sequence of the plasmid, which had 21 vmp gene sequences (designated as vmpA to U) (40). To date, the complete genomic sequence of the Lyme disease spirochete B. burgdorferi strain B31 has revealed over 150…”