Affiliation:
1. Center for Microbial Pathogenesis1 and Departments of
2. Department of Microbiology, University of Texas Southwestern Medical Center, Dallas, Texas 75235;2 and
3. Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 731903
4. Medicine4 and
5. Microbiology,5 University of Connecticut Health Center, Farmington, Connecticut 06030;
Abstract
ABSTRACT
In this study, we characterized seven members of the cp32/18 family of supercoiled plasmids in
Borrelia burgdorferi
297. Complete sequence analysis of a 21-kb plasmid (cp18-2) confirmed that the strain 297 plasmids are similar in overall content and organization to their B31 counterparts. Of the 31 open reading frames (ORFs) in cp18-2, only three showed sequence relatedness to proteins with known functions, and only one, a ParA/SopA ortholog, was related to nonborrelial polypeptides. Besides the lipoproteins, none of the ORFs appeared likely to encode a surface-exposed protein. Comparison with the B31 genomic sequence indicated that paralogs for most of the ORFs in cp18-2 can be identified on other genetic elements. cp18-2 was found to lack a 9- to 10-kb fragment present in the 32-kb homologs which, by extrapolation from the B31 cp32 sequences, contains at least 15 genes presumed to be unnecessary for plasmid maintenance. Sequence analysis of the lipoprotein-encoding variable loci provided evidence that recombinatorial processes within these regions may result in the acquisition of exogenous DNA. Pairwise analysis with random shuffling revealed that the multiple lipoproteins (Mlp; formerly designated 2.9 LPs) fall into two distinct homology groups which appear to have arisen by gene fusion events similar to those recently proposed to have generated the three OspE, OspF, and Elp lipoprotein families (D. R. Akins, M. J. Caimano, X. Yang, F. Cerna, M. V. Norgard, and J. D. Radolf, Infect. Immun. 67:1526–1532, 1999). Comparative analysis of the variable regions also indicated that recombination within the loci of each plasmid may occur independently. Last, comparison of variable loci revealed that the cp32/18 plasmid complements of the B31 and 297 isolates differ substantially, indicating that the two strains have been subject to divergent adaptive pressures. In addition to providing evidence for two different types of recombinatorial events involving cp32/18 plasmids, these findings underscore the need for genetic analysis of diverse borrelial isolates in order to elucidate the Lyme disease spirochete's complex parasitic strategies.
Publisher
American Society for Microbiology
Subject
Infectious Diseases,Immunology,Microbiology,Parasitology
Cited by
47 articles.
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