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Regulatory protein BBD18 of the lyme disease spirochete: essential role during tick acquisition?

ABSTRACT: The Lyme disease spirochete Borrelia burgdorferi senses and responds to environmental cues as it transits between the tick vector and vertebrate host. Failure to properly adapt can block transmission of the spirochete and persistence in either vector or host. We previously identified BBD18, a novel plasmid-encoded protein of B. burgdorferi, as a putative repressor of the host-essential factor OspC. In this study, we investigate the in vivo role of BBD18 as a regulatory protein, using an experimental mouse-tick model system that closely resembles the natural infectious cycle of B. burgdorferi. We show that spirochetes that have been engineered to constitutively produce BBD18 can colonize and persist in ticks but do not infect mice when introduced by either tick bite or needle inoculation. Conversely, spirochetes lacking BBD18 can persistently infect mice but are not acquired by feeding ticks. Through site-directed mutagenesis, we have demonstrated that abrogation of spirochete infection in mice by overexpression of BBD18 occurs only with bbd18 alleles that can suppress OspC synthesis. Finally, we demonstrate that BBD18-mediated regulation does not utilize a previously described ospC operator sequence required by B. burgdorferi for persistence in immunocompetent mice. These data lead us to conclude that BBD18 does not represent the putative repressor utilized by B. burgdorferi for the specific downregulation of OspC in the mammalian host. Rather, we suggest that BBD18 exhibits features more consistent with those of a global regulatory protein whose critical role occurs during spirochete acquisition by feeding ticks. IMPORTANCE Lyme disease, caused by Borrelia burgdorferi, is the most common arthropod-borne disease in North America. B. burgdorferi is transmitted to humans and other vertebrate hosts by ticks as they take a blood meal. Transmission between vectors and hosts requires the bacterium to sense changes in the environment and adapt. However, the mechanisms involved in this process are not well understood. By determining how B. burgdorferi cycles between two very different environments, we can potentially establish novel ways to interfere with transmission and limit infection of this vector-borne pathogen. We are studying a regulatory protein called BBD18 that we recently described. We found that too much BBD18 interferes with the spirochete's ability to establish infection in mice, whereas too little BBD18 appears to prevent colonization in ticks. Our study provides new insight into key elements of the infectious cycle of the Lyme disease spirochete.

SUBMITTER: Hayes BM

PROVIDER: S-EPMC3977360 | biostudies-literature | 2014 Apr

REPOSITORIES: biostudies-literature

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Regulatory protein BBD18 of the lyme disease spirochete: essential role during tick acquisition?

Hayes Beth M BM Dulebohn Daniel P DP Sarkar Amit A Tilly Kit K Bestor Aaron A Ambroggio Xavier X Rosa Patricia A PA

mBio 20140401 2

The Lyme disease spirochete Borrelia burgdorferi senses and responds to environmental cues as it transits between the tick vector and vertebrate host. Failure to properly adapt can block transmission of the spirochete and persistence in either vector or host. We previously identified BBD18, a novel plasmid-encoded protein of B. burgdorferi, as a putative repressor of the host-essential factor OspC. In this study, we investigate the in vivo role of BBD18 as a regulatory protein, using an experime ...[more]

PMID: 24692636

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Project description:UnlabelledThe Lyme disease spirochete Borrelia burgdorferi has five putative methyl-accepting chemotaxis proteins (MCPs). In this report, we provide evidence that a hypothetical protein, BB0569, is essential for the chemotaxis of B. burgdorferi. While BB0569 lacks significant homology to the canonical MCPs, it contains a conserved domain (spanning residues 110 to 170) that is often evident in membrane-bound MCPs such as Tar and Tsr of Escherichia coli. Unlike Tar and Tsr, BB0569 lacks transmembrane regions and recognizable HAMP and methylation domains and is similar to TlpC, a cytoplasmic chemoreceptor of Rhodobacter sphaeroides. An isogenic mutant of BB0569 constantly runs in one direction and fails to respond to attractants, indicating that BB0569 is essential for chemotaxis. Immunofluorescence, green fluorescent protein (GFP) fusion, and cryo-electron tomography analyses demonstrate that BB0569 localizes at the cell poles and is required for chemoreceptor clustering at the cell poles. Protein cross-linking studies reveal that BB0569 forms large protein complexes with MCP3, indicative of its interactions with other MCPs. Interestingly, analysis of B. burgdorferi mcp mutants shows that inactivation of either mcp2 or mcp3 reduces the level of BB0569 substantially and that such a reduction is caused by protein turnover. Collectively, these results demonstrate that the domain composition and function of BB0569 are similar in some respects to those of TlpC but that these proteins are different in their cellular locations, further highlighting that the chemotaxis of B. burgdorferi is unique and different from the Escherichia coli and Salmonella enterica paradigm.ImportanceSpirochete chemotaxis differs substantially from the Escherichia coli and Salmonella enterica paradigm, and the basis for controlling the rotation of the bundles of periplasmic flagella at each end of the cell is unknown. In recent years, Borrelia burgdorferi, the causative agent of Lyme disease, has been used as a model organism to understand spirochete chemotaxis and its role in infectious processes of the disease. In this report, BB0569, a hypothetical protein of B. burgdorferi, has been investigated by using an approach of genetic, biochemistry, and cryo-electron tomography analyses. The results indicate that BB0569 has a distinct role in chemotaxis that may be unique to spirochetes and represents a novel paradigm.

Project description:The alternative sigma factor RpoS plays a central role in the critical host-adaptive response of the Lyme disease spirochete, Borrelia burgdorferi. We previously identified bbd18 as a negative regulator of RpoS but could not inactivate bbd18 in wild-type spirochetes. In the current study we employed an inducible bbd18 gene to demonstrate the essential nature of BBD18 for viability of wild-type spirochete viability in vitro and at a unique point in vivo. Transcriptomic analyses of BBD18 depleted cells demonstrated global induction of RpoS-dependent genes prior to lysis, with the absolute requirement for BBD18, both in vitro and in vivo, circumvented by deletion of rpoS. The increased expression of plasmid prophage genes and the presence of phage particles in the supernatants of lysing cultures indicate that RpoS regulates phage lysis-lysogeny decisions. Through this work we identify a mechanistic link between endogenous transducing prophages and the RpoS-dependent adaptive response of the Lyme disease spirochete. The alternative sigma factor RpoS plays a central role in the critical host-adaptive response of the Lyme disease spirochete, Borrelia burgdorferi. We previously identified bbd18 as a negative regulator of RpoS but could not inactivate bbd18 in wild-type spirochetes. In the current study we employed an inducible bbd18 gene to demonstrate the essential nature of BBD18 for viability of wild-type spirochete viability in vitro and at a unique point in vivo. Transcriptomic analyses of BBD18 depleted cells demonstrated global induction of RpoS-dependent genes prior to lysis, with the absolute requirement for BBD18, both in vitro and in vivo, circumvented by deletion of rpoS. The increased expression of plasmid prophage genes and the presence of phage particles in the supernatants of lysing cultures indicate that RpoS regulates phage lysis-lysogeny decisions. Through this work we identify a mechanistic link between endogenous transducing prophages and the RpoS-dependent adaptive response of the Lyme disease spirochete.

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Regulatory protein BBD18 of the lyme disease spirochete: essential role during tick acquisition?

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Regulatory protein BBD18 of the lyme disease spirochete: essential role during tick acquisition?

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