Altered Murine Tissue Colonization by Borrelia burgdorferi following Targeted Deletion of Linear Plasmid 17-Carried Genes

Abstract

<jats:title>ABSTRACT</jats:title><jats:p>The causative agent of Lyme disease,<jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">Borrelia burgdorferi</jats:named-content>, possesses a segmented genome comprised of a single linear chromosome and upwards of 23 linear and circular plasmids. Much of what is known about plasmid-borne genes comes from studying laboratory clones that have spontaneously lost one or more plasmids during<jats:italic>in vitro</jats:italic>passage. Some plasmids, including the linear plasmid lp17, are never or rarely reported to be lost during routine culture; therefore, little is known about the requirement of these conserved plasmids for infectivity. In this study, the effects of deleting regions of lp17 were examined both<jats:italic>in vitro</jats:italic>and<jats:italic>in vivo</jats:italic>. A mutant strain lacking the genes<jats:italic>bbd16</jats:italic>to<jats:italic>bbd25</jats:italic>showed no deficiency in the ability to establish infection or disseminate to the bloodstream of mice; however, colonization of peripheral tissues was delayed. Despite the ability to colonize ear, heart, and joint tissues, this mutant exhibited a defect in bladder tissue colonization for up to 56 days postinfection. This phenotype was not observed in immunodeficient mice, suggesting that bladder colonization by the mutant strain was inhibited by an adaptive immune-based mechanism. Moreover, the mutant displayed increased expression of outer surface protein C<jats:italic>in vitro</jats:italic>, which was correlated with the absence of the gene<jats:italic>bbd18</jats:italic>. To our knowledge, this is the first report involving genetic manipulation of lp17 in an infectious clone of<jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">B. burgdorferi</jats:named-content>and reveals for the first time the effects of lp17 gene deletion during murine infection by the Lyme disease spirochete.</jats:p>

Regulatory Protein BBD18 of the Lyme Disease Spirochete: Essential Role During Tick Acquisition?

“…This represents the approach we used initially to identify BBD18 as an OspC repressor (30), as well as that subsequently used by Casselli et al to investigate the role of lp17 genes during mouse infection by B. burgdorferi (38). To this end, we displaced the full-length plasmid from WT B. burgdorferi with two different truncated forms of lp17.…”

Borrelia chilensis, a new member of theBorrelia burgdorferisensu lato complex that extends the range of this genospecies in theSouthernHemisphere

“…4). The absence of lp17 in B. by both PFGE and PCR analyses could indicate a modified pathogenicity for rodents, since targeted deletion of genes on this plasmid altered tissue invasion in mice (Casselli et al, 2012). Another plasmid associated with borrelial pathogenicity for rodents, lp36 (Purser and Norris, 2000; Jewett et al, 2007), could not be amplified from B. chilensis by PCR, but its presence in PFGE analysis could not be definitively determined because of the multiplicity of mid-range sized plasmids visible on the gel.…”

Bacterial Heterogeneity Is a Requirement for Host Superinfection by the Lyme Disease Spirochete

“…Urinary bladder tissue has been shown to be a consistent source of culture-detectable spirochetes from B. burgdorferiinfected rodents (43)(44)(45)(46)(47)(48). However, a recent study reported that an infectious B. burgdorferi mutant (B31 5A4⌬D16-D25) lacking lp17-resident genes bbd16 to bbd25 exhibited an impaired ability to colonize bladder tissue in C3H mice (23). To test the hypothesis that an uncolonized murine bladder could serve as an available niche for a superinfecting homologous clone of B. burgdorferi, the bladder-colonizing-defective mutant was utilized for the superinfection assay (Fig.…”