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Chapter 6 : Comparative Pathogenomics of Spirochetes
Category: Genomics and Bioinformatics; Bacterial Pathogenesis
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This chapter reports on three pathogenic spirochetes: Treponema pallidum, causative agent of syphilis, and other treponemes; Borrelia burgdorferi, causative agent of Lyme disease, and related species; and Leptospira species, responsible for leptospirosis. The spirochetes are quite different from many of the other well-studied pathogens that are principally found in the proteobacteria and gram-positive groups. Treponema paraluiscuniculi is not pathogenic for humans and causes veneral spirochetosis in rabbits. Differences in the chromosome sequence can be used for molecular diagnostic testing of treponemal subspecies and strains and for epidemiological studies. The genome sequence information enables new approaches to be developed to determine the function of genes and their possible role in pathogenesis. To identify antigens important in the human immune response to syphilis, the serum antibody reactivity of patients with syphilis was examined with 908 T. pallidum proteins by using the same techniques as those for the rabbit sera. The genus Borrelia comprises spirochetes with loose wavelike coils that survive exclusively by transmission back and forth between vertebrate and arthropod hosts. The chromosome of B. burgdorferi encodes most of the housekeeping genes required for in vitro survival and growth, as demonstrated by strain B. burgdorferi B313, which has lost most of the plasmids. Leptospira is found in many animal species, and this broad reservoir provides a continuous source for infection, making this one of the most widespread zoonotic infections.
Comparison of genome differences found in T. pallidum subsp. pertenue Samoa D and in T. paraluiscuniculi Cuniculi A genomes when compared with the T. pallidum subsp. pallidum Nichols and SS14 genomes. Numbers in boxes represent the number of additional or missing restriction target sites in Samoa D and Cuniculi A genomes compared with the Nichols genome. Four chromosomal regions with indels present in SS14, Samoa D, and Cuniculi A genomes are not shown.
Mapping stage of CGS strategy. Results obtained for T. pallidum subsp. pallidum SS14, T. pallidum subsp. pertenue Samoa D, and T. paraluiscuniculi Cuniculi A are shown. Oligonucleotides showing significantly lower hybridization in the tested genome are shown as vertical bars and indicate sequence heterogeneity in these regions when compared with the Nichols reference genome. Note the increasing amount of sequence diversity in the order SS14, Samoa D, and Cuniculi A strains. ORFs of Nichols (both strands) are shown at the top.
Univector plasmid fusion system. Cre-loxP–mediated site-specific recombination fuses the pUNI and pHOST plasmids at the loxP site. As a result, the gene of interest is placed under the control of the pHOST promoter and fused to any Tag sequences present in the pHOST plasmid. Figure adapted from references 45 and 49 .
Identification of antigenic proteins in the T. pallidum proteome. The proteins arrayed for the immunoassay are presented numerically along the x axis according to their ORF number, TP0001 to TP1041. Chemiluminescence from a secondary anti-rabbit antibody conjugated to horseradish peroxidase was used to monitor rabbit antibody binding to GST fusion proteins and is measured in relative light units, shown along the y axis. T. pallidum fusion proteins that exhibited the highest levels of antibody binding are labeled. Figure adapted from reference 48 .
Transmission cycle and protein expression changes of the Lyme disease spirochete, Borrelia burgdorferi. The expression of many proteins is upregulated or downregulated in the transition between arthropod and mammalian hosts, as exemplified by OspA, OspC, DbpA, and DbpB. From reference 54 , used with permission.
Complex genome structure of Borrelia species, as exemplified by B. burgdorferi B31 ( 14 , 23 ). Extrachromosomal elements include both linear plasmids (lp) and circular plasmids; the approximate sizes in kilobase pairs are specified in the plasmid names. Closely related sequences are indicated by dark shading and patterns. The cp32 plasmids resemble prophages, and an additional copy of a cp32-related sequence is embedded in lp54. Similarly, lp21 contains a complete copy of lp5 bifurcated by an intervening sequence.
Pathogenic spirochetes and diseases they cause
Potential virulence determinants of Borrelia burgdorferi (partial listing)
Leptospira genomes Genome size (Mb) No. of CDS