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Feria-Arroyo et al. had reported previously that, based on PCR analysis, 45% of Ixodes scapularis ticks collected in Texas and Mexico were infected with the Lyme disease spirochete Borrelia burgdorferi (Parasit. Vectors 2014, 7:199). However, our analyses of their initial data (Parasit. Vectors 2014, 7:467) and a recent response by Esteve-Gassent et al. (Parasit. Vectors 2015, 8:129) provide evidence that the positive PCR results obtained from both ribosomal RNA intergenic sequences and the flagellin gene flaB are highly likely due to contamination by the B. burgdorferi B31 positive control strain.

The bacterial flagellar motor is a remarkable nanomachine that provides motility through flagellar rotation. Prior structural studies have revealed the stunning complexity of the purified rotor and C-ring assemblies from flagellar motors. In this study, we used high-throughput cryo-electron tomography and image analysis of intact Borrelia burgdorferi to produce a three-dimensional (3-D) model of the in situ flageilar motor without imposing rotational symmetry. Structural details of B. burgdorferi, including a layer of outer surface proteins, were clearly visible in the resulting 3-D reconstructions. By averaging the 3-D images of ~1,280 flagellar motors, a ~3.5-nm-resolution model of the stator and rotor structures was obtained.flgI transposon mutants lacked a torus-shaped structure attached to the flagellar rod, establishing the structural location of the spirochetal P ring. Treatment of intact organisms with the nonionic detergent NP-40 resulted in dissolution of the outermost portion of the motor structure and the C ring, providing insight into the in situ arrangement of the stator and rotor structures. Structural elements associated with the stator followed the curvature of the cytoplasmic membrane. The rotor and the C ring also exhibited angular flexion, resulting in a slight narrowing of both structures in the direction perpendicular to the cell axis. These results indicate an inherent flexibility in the rotor-stator interaction. The FliG switching and energizing component likely provides much of the flexibility needed to maintain the interaction between the curved stator and the relatively symmetrical rotor/C-ring assembly during flagellar rotation.

The Lyme disease agent Borrelia burgdorferi can persistently infect humans and other animals despite host active immune responses. This is facilitated, in part, by the vls locus, a complex system consisting of the vlsE expression site and an adjacent set of 11 to 15 silent vls cassettes. Segments of nonexpressed cassettes recombine with the vlsE region during infection of mammalian hosts, resulting in combinatorial antigenic variation of the VisE outer surface protein. We now demonstrate that synthesis of VisE is regulated during the natural mammal-tick infectious cycle, being activated in mammals but repressed during tick colonization. Examination of cultured B. burgdorferi cells indicated that the spirochete controls vise transcription levels in response to environmental cues. Analysis of PvlsE::gfp fusions in B. burgdorferi indicated that VisE production is controlled at the level of transcriptional initiation, and regions of 5' DNA involved in the regulation were identified. Electrophoretic mobility shift assays detected qualitative and quantitative changes in patterns of protein-DNA complexes formed between the vise promoter and cytoplasmic proteins, suggesting the involvement of DNA-binding proteins in the regulation of vlsE, with at least one protein acting as a transcriptional activator.

RNA transcript levels in the syphilis spirochete Treponema pallidum subsp. pallidum (Nichols) isolated from experimentally infected rabbits were determined by the use of DNA microarray technology. This characterization of the T. pallidum transcriptome during experimental infection provides further insight into the importance of gene expression levels for the survival and pathogenesis of this bacterium.

Researchers have identified and characterized an elaborate genetic system in the Lyme disease spirochete Borrelia burgdorferi that promotes antigenic variation of a surface-exposed lipoprotein. A variable major protein (vmp)-like sequence locus that is similar to the vmp system for antigenic variation of relapsing fever organisms was found in the linear plasmid of B. burgdorferi B31. The antigenic variation of the expressed lipoprotein may produce millions of antigenic variants in the mammalian host.

The morphology of Treponema denticola cells was analyzed by dark-field microscopy to determine the influence of the periplasmic flagella (PF) on cell structure. The wild-type Treponema denticola cells in broth and methylcellulose culture media exhibited irregular twisted morphology with planar and helical regions. On the other hand, PF-deficient mutants exhibited distinctive helical morphology and impaired motility. The effects of PF-deficiency indicated the role of the PFs in mediating cell motility and irregular cell morphology.

Treponema pallidum is different from other spirochetes because it contains cytoplasmic filaments underneath the cytoplasmic membrane. Cloning and expression of the cytoplasmic filament protein gene cfpA of Treponema pallidum subsp. pallidum Nichols identified three components of the gene: a 2,034-nucleotide coding region; a putative promoter region; and a putative ribosome-binding site. Sequence analysis indicated a protein of 678 residues with a molecular mass of 78.5 kilodaltons and an isoelectric potential of 6.15. It was suggested that T. pallidum cytoplasmic filaments may be a unique form of prokaryotic intracytoplasmic inclusions.

Characterization of the genomic organization of spirochetes of the genus Borrelia by pulsed-field gel electrophoresis revealed a linear chromosome about 1 Mb in size and multiple linear plasmids in the 16- to 200-kb size range. Two forms of plasmids were observed, linear and circular. The shape of the plasmids had no effect on the behavior of the species bearing either form of the plasmids. However, conversion from the linear form to the circular form of the plasmid was observed in the relapsing fever agent B. hermsii.

Restriction fragments produced by NotI, SfiI and SrfI formulated a physical map of the chromosome of Treponema pallidum subsp. pallidum (Nichols) of the length of approximately 1,030 to 1,080 kbp is size, which is the causative agent of syphilis. This restriction cleaved the T. pallidum genome in to 16,8 and 15 fragments. The process of construction of this physical map is discussed.

Abstract Background Syphilis spirochete Treponema pallidum ssp. pallidum remains the enigmatic pathogen, since no virulence factors have been identified and the pathogenesis of the disease is poorly understood. Increasing rates of new syphilis cases per year have been observed recently. Results The genome of the SS14 strain was sequenced to high accuracy by an oligonucleotide array strategy requiring hybridization to only three arrays (Comparative Genome Sequencing, CGS). Gaps in the resulting sequence were filled with targeted dideoxy-terminators (DDT) sequencing and the sequence was confirmed by whole genome fingerprinting (WGF). When compared to the Nichols strain, 327 single nucleotide substitutions (224 transitions, 103 transversions), 14 deletions, and 18 insertions were found. On the proteome level, the highest frequency of amino acid-altering substitution polymorphisms was in novel genes, while the lowest was in housekeeping genes, as expected by their evolutionary conservation. Evidence was also found for hypervariable regions and multiple regions showing intrastrain heterogeneity in the T. pallidum chromosome. Conclusion The observed genetic changes do not have influence on the ability of Treponema pallidum to cause syphilitic infection, since both SS14 and Nichols are virulent in rabbit. However, this is the first assessment of the degree of variation between the two syphilis pathogens and paves the way for phylogenetic studies of this fascinating organism.