Rrp1, a cyclic‐di‐GMP‐producing response regulator, is an important regulator of Borrelia burgdorferi core cellular functions

Abstract

SummaryTwo-component systems (TCS) are universal among bacteria and play critical roles in gene regulation. Our understanding of the contributions of TCS in the biology of the Borrelia is just now beginning to develop. Borrelia burgdorferi, a causative agent of Lyme disease, harbours a TCS comprised of open reading frames (ORFs) BB0419 and BB0420. BB0419 encodes a response regulator designated Rrp1, and BB0420 encodes a hybrid histidine kinase-response regulator designated Hpk1. Rrp1, which contains a conserved GGDEF domain, undergoes phosphorylation and produces the secondary messenger, cyclic diguanylate (c-di-GMP), a critical signaling molecule in numerous organisms. However, the regulatory role of the Rrp1-Hpk1 TCS and c-di-GMP signaling in Borrelia biology are unexplored. In this study, the distribution, conservation, expression and potential global regulatory capability of Rrp1 were assessed. rrp1 was found to be universal and highly conserved among isolates, co-transcribed with hpk1, constitutively expressed during in vitro cultivation, and significantly upregulated upon tick feeding. Allelic exchange replacement and microarray analyses revealed that the Rrp1 regulon consists of a large number of genes encoded by the core Borrelia genome (linear chromosome, linear plasmid 54 and circular plasmid 26) that encode for proteins involved in central metabolic processes and virulence mechanisms including immune evasion.

The Hybrid Histidine Kinase Hk1 Is Part of a Two-Component System That Is Essential for Survival of Borrelia burgdorferi in Feeding Ixodes scapularis Ticks

“…Microarray analyses of a ⌬rrp1 mutant indentified 140 genes whose expression was influenced by this RR in vitro (58), several of which encode proteins whose annotated functions suggest a role in carbon metabolism, maintenance of the spirochete's cell envelope, and adaptation to the arthropod vector and/or mammalian host. However, because the background used to generate this ⌬rrp1 mutant was avirulent (58), the contribution of Rrp1 to virulence could not be determined. Therefore, to determine the role of the Hk1/Rrp1 TCS during the enzootic cycle, we sought to inactivate both genes within a virulent strain 297 background.…”

“…(C) Detection of Rrp1 by immunoblotting. Whole-cell lysates of CE162 (WT 297), Bb508 (hk1-KO), and a previously characterized B31 5A13 ⌬rrp1 isolate (58) were immunoblotted with rat polyclonal antisera directed against Rrp1 (58) with FlaB used as a loading control. ␣, anti.…”

Gene Regulation, Two Component Regulatory Systems, and Adaptive Responses in Treponema Denticola

“…Perhaps most notable is the potential global regulatory role of the secondary messenger, c-di-GMP, which most certainly plays an important role in the biology and pathogenesis of T. denticola (Bian et al 2013). C-di-GMP mediated regulation has been studied in depth in a long and diverse list of bacteria, including spirochete species associated with Lyme disease and relapsing fever (Caimano et al 2015;Kostick et al 2011;Mallory et al 2016;Pitzer et al 2011;Rogers et al 2009;Ryjenkov et al 2005;Sultan et al 2010). C-di-GMP is produced by diguanylate cyclases (DGC) which can be identified by the presence of the signature GGDEF domain (Hengge 2009).…”

Molecular Signaling Mechanisms of the Periopathogen, Treponema denticola

“…The importance of c-di-GMP in spirochetal biology is highlighted by recent studies of B. burgdorferi (Ryjenkov et al, 2005;Rogers et al, 2009;Freedman et al, 2009;Sultan et al, 2010). B. burgdorferi encodes a single diguanylate cyclase designated as response regulatory protein 1 (Rrp1).…”