Contribution of RpoS to persistence of Borrelia burgdorferi in mammals

Abstract
It is now universally accepted that the alternative sigma factor RpoS serves as a master regulator for differential
gene expression in Bb. Using a novel enrichment RNAseq technique, we established that the RpoS regulon
changes dramatically as spirochetes undergo mammalian host adaptation and that the mammalian phase RpoS
regulon includes virulence determinants required for early infection. The unexpected discovery that the
BosR/RpoS regulon includes vlsE was a clear indicator that RpoS is needed not only to establish infection but
also to maintain it. Using a rpoS mutant complemented with an IPTG-inducible rpoS allele, we established that
Bb do not survive in mice once RpoS is turned OFF and that persistence involves elements within the RpoS
regulatory network functionally unrelated to evasion of adaptive immunity. These findings set the stage for Aims
to achieve our overarching objective – elucidating how RpoS-dependent gene regulation perpetuates the
mammalian phase of the spirochete's enzootic cycle. In Aim 1, we use our IPTG-inducible system for controlling
borrelial gene expression in vivo interrogation individual RpoS-regulated genes in specific milieus and time
points throughout the course of murine infection. In Aim 2, we dissect the topological features and promoter
elements used by RpoS, BosR and YebC to collaboratively control expression of vlsE and determine the
relationship between expression of vlsE and switching in vivo. The proposed experiments will shed new light on
how LD spirochetes persist in nature, the ecological substrate for human disease, as well as how they persist in
human tissues, giving rise to the chronic, debilitating clinical manifestations that make them a major threat to
health and wellbeing.

Grant Number: 1R21AI187932-01
NIH Institute/Center: NIH
Principal Investigator: MELISSA CAIMANO