# RpoS Regulation of Borrelia burgdorferi Genes in vivo

> **NIH NIH R01** · UNIVERSITY OF CONNECTICUT SCH OF MED/DNT · 2022 · $593,760

## Abstract

Borrelia burgdorferi (Bb), the agent of Lyme disease (LD), is maintained in nature within a complex enzootic
cycle involving a mammalian reservoir host and a tick vector. To sustain this cycle, Bb must adjust its
transcriptome, proteome, and metabolome to arthropod- and mammalian host-derived signals as it shuttles
between the two. The Rrp2/RpoN/RpoS pathway has gained widespread recognition as a central player in
borrelial gene regulation. Our laboratory has long been at the forefront of efforts to characterize the cohort of
genes controlled by RpoS in both the tick and mammal. Unfortunately, we still do not know the entire output of
RpoS-RNA polymerase (RNAP) holoenzyme in nature. The present proposal addresses this shortfall by
combining state-of-the-art transcriptomic and mutagenesis methodologies to determine where/when individual
genes contribute to RpoS's dual-host `mission'. In prior publications, we were instrumental in delineating the
temporal boundaries of the RpoS-ON and –OFF states in vivo. In recent years, however, our thinking about this
dichotomy has become much more nuanced. We now believe that the contours of the RpoS regulon change
profoundly and in host-specific fashion during the RpoS-ON state These results, in concert with studies of the
Hk1/Rrp1 pathway, give rise to our central hypothesis--the dynamic nature of the RpoS regulon reflects the
confluence of non-RpoS regulatory pathways with mechanisms that govern the ON/OFF states of RpoS and the
output of RpoS-RNAP. Along these lines, we now propose that the tick-phase signaling molecule c-di-GMP is
crucial to this regulatory cross-talk. Moreover, we and others have found that the c-di-GMP-binding protein PlzA
promotes expression of RpoS and, hence, Bb virulence in the mouse, the stage of the enzootic cycle in which the
Hk1/Rrp1 pathway is OFF. Our efforts to clarify this bifunctional role of PlzA as a mediator of c-di-GMP signaling
in ticks and a c-di-GMP-independent regulator of RpoS in mice takes our field into uncharted territory. Lastly,
in years past, our analysis of mammalian host-adapted spirochetes cultivated in dialysis membrane chambers
revealed that RpoS not only upregulates genes required for tick transmission and mammalian infection but also
represses genes required for colonization and adaptation to the tick. Our recent work suggests that RpoS-RNAP
directly represses transcription of tick-phase genes by occluding their σ70 promoters. We will test this `RpoS as
repressor' model and explore new data that c-di-GMP antagonizes RpoS-mediated repression in mammalian
host-adapted Bb. Our long-term objective is to achieve an integrative understanding of how the
Rrp2/RpoN/RpoS pathway fulfills its essential mission--guiding LD spirochetes from tick to mouse and back
again. We will accomplish this by defining the contours of the RpoS regulon in ticks and mice (Aim 1); clarifying
the convergence of c-di-GMP- and PlzA-dependent signaling with the RpoS pathway (Aim 2); and...

## Key facts

- **NIH application ID:** 10459323
- **Project number:** 5R01AI029735-31
- **Recipient organization:** UNIVERSITY OF CONNECTICUT SCH OF MED/DNT
- **Principal Investigator:** MELISSA J CAIMANO
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $593,760
- **Award type:** 5
- **Project period:** 1990-04-01 → 2024-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10459323

## Citation

> US National Institutes of Health, RePORTER application 10459323, RpoS Regulation of Borrelia burgdorferi Genes in vivo (5R01AI029735-31). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10459323. Licensed CC0.

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