BosR and PlzA reciprocally regulate RpoS function to sustain Borrelia burgdorferi in ticks and mammals
André A. Grassmann, … , Justin D. Radolf, Melissa J. Caimano
André A. Grassmann, … , Justin D. Radolf, Melissa J. Caimano
Published January 17, 2023
Citation Information: J Clin Invest. 2023;133(5):e166710. https://doi.org/10.1172/JCI166710.
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Research Article Infectious disease Microbiology

BosR and PlzA reciprocally regulate RpoS function to sustain Borrelia burgdorferi in ticks and mammals

Abstract

The RNA polymerase alternative σ factor RpoS in Borrelia burgdorferi (Bb), the Lyme disease pathogen, is responsible for programmatic-positive and -negative gene regulation essential for the spirochete’s dual-host enzootic cycle. RpoS is expressed during tick-to-mammal transmission and throughout mammalian infection. Although the mammalian-phase RpoS regulon is well described, its counterpart during the transmission blood meal is unknown. Here, we used Bb-specific transcript enrichment by tick-borne disease capture sequencing (TBDCapSeq) to compare the transcriptomes of WT and ΔrpoS Bb in engorged nymphs and following mammalian host-adaptation within dialysis membrane chambers. TBDCapSeq revealed dramatic changes in the contours of the RpoS regulon within ticks and mammals and further confirmed that RpoS-mediated repression is specific to the mammalian-phase of Bb’s enzootic cycle. We also provide evidence that RpoS-dependent gene regulation, including repression of tick-phase genes, is required for persistence in mice. Comparative transcriptomics of engineered Bb strains revealed that the Borrelia oxidative stress response regulator (BosR), a noncanonical Fur family member, and the cyclic diguanosine monophosphate (c-di-GMP) effector PlzA reciprocally regulate the function of RNA polymerase complexed with RpoS. BosR is required for RpoS-mediated transcription activation and repression in addition to its well-defined role promoting transcription of rpoS by the RNA polymerase alternative σ factor RpoN. During transmission, ligand-bound PlzA antagonizes RpoS-mediated repression, presumably acting through BosR.

Authors

André A. Grassmann, Rafal Tokarz, Caroline Golino, Melissa A. McLain, Ashley M. Groshong, Justin D. Radolf, Melissa J. Caimano

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Figure 6

Proposed model for the reciprocal regulation of the RpoS gatekeeper by BosR and ligand-bound PlzA.

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Proposed model for the reciprocal regulation of the RpoS gatekeeper by B...
Top: Transcription of rpoS by RNAP complexed with BosR/Rrp2/RpoN in feeding nymphs and mammals is unaffected by either c-di-GMP (yellow circle) or PlzA. Left: In mammals, BosR enhances transcription of RpoS-upregulated core and DMC-only genes and is required for RpoS-mediated repression of tick-phase genes. RNAP-RpoS/BosR complex binds upstream of RpoS-repressed tick-phase genes, including ospA and the glp operon, preventing transcription by RNAP-RpoD. Due to the absence of c-di-GMP within mammals, apo PlzA is unable to interact with RNAP and/or prevent BosR’s σ activator function. Right: In feeding nymphs, ligand-bound PlzA interferes with BosR function, reducing expression of some RpoS-upregulated genes, including ospC, dbpA, and vlsE, and antagonizing RpoS-mediated repression either by blocking BosR binding to RNAP-RpoS or allosteric interactions with RNAP-RpoS/BosR. Based on this model, BosR’s σ activator function is specific to RNAP-RpoS, while ligand-bound PlzA interacts with both RNAP-RpoS and RNAP-RpoD in feeding nymphs. Ligand-bound PlzA also is required for RpoD-dependent transcription of glp genes, while tick-phase genes with strong promoters, such as ospA, are transcribed by RNAP-RpoD alone.