Contributions of Environmental Signals and Conserved Residues to the Functions of Carbon Storage Regulator A of Borrelia burgdorferi

Abstract

Carbon storage regulator A of Borrelia burgdorferi (CsrA Bb ) contributes to vertebrate host-specific adaptation by modulating activation of the Rrp2-RpoN-RpoS pathway and is critical for infectivity. We hypothesized that the functions of CsrA Bb are dependent on environmental signals and on select residues. We analyzed the phenotype of csrA Bb deletion and site-specific mutants to determine the conserved and pathogen-specific attributes of CsrA Bb

FliW antagonizes CsrA RNA binding by a noncompetitive allosteric mechanism

“…Recent work in the distantly related C. jejuni is consistent with the B. subtilis model, in which FliW antagonizes CsrA and CsrA inhibits flagellin translation (39). Thus, the noncompetitive mechanism of inhibition that governs the CsrA-FliW-flagellin module is likely to be directly applicable to all FliW-encoding organisms, including members of the firmicutes, the spirochetes, and the deep branches of the proteobacteria (34,39,(45)(46)(47)(48). In contrast, competitive inhibition of CsrA by sRNA has been extensively studied, but only in bacteria belonging to the family of γ-proteobacteria (29).…”

“…The phylogenetic distribution of sRNA competitors is poorly understood because of difficulties in predicting sRNA presence, expression, and function, but the conservation of the BarA-UvrY two component system that regulates csrB and csrC expression is largely restricted to the γ-proteobacteria, suggesting the sRNA mechanism of CsrA antagonism is narrowly distributed (34,38,49). Finally we note that, whether an organism uses sRNAs or FliW for regulation, CsrA regulates virulence factors in each pathogen in which it has been studied (1,(45)(46)(47)(48). We suggest that CsrA is a candidate therapeutic target and that the precedent for noncompetitive inhibition can be exploited to isolate noncompetitive inhibitors, which are typically effective at lower doses than competitive counterparts.…”

CsrA (BB0184) Is Not Involved in Activation of the RpoN-RpoS Regulatory Pathway in Borrelia burgdorferi

“…Because all previous csrA mutants ( [42][43][44][45] were created in B. burgdorferi strain B31, we also created two mutants (OY153/B7 and OY153/ B12) deficient in csrA in this strain. By introducing the suicide plasmid pOY236 into the low-passage virulent strain B31, we obtained two kanamycin-resistant csrA mutants (Fig.…”

“…Consequently, our original csrA mutant (AH227) lacked the virulence-associated plasmids lp25 and lp28-1, which precluded us at that time from assessing a role for CsrA in B. burgdorferi mouse infectivity and pathogenesis. However, recent reports implicating CsrA in a potential layer of control over the RpoN-RpoS regulatory pathway (42)(43)(44)(45) prompted us to reassess the role(s) of CsrA in B. burgdorferi gene expression and pathogenesis, with emphasis on attempting to reconcile a number of paradoxes and contradictions. In contrast to recent findings (42)(43)(44)(45), our data from this study clearly demonstrate that CsrA does not impact the expression of rpoS or RpoS-dependent ospC and dbpA in B. burgdorferi.…”

“…Although many molecular details behind the activation of rpoS by BosR remain unknown, our recent studies revealed that BosR directly activates rpoS transcription through binding to a novel DNA sequence (38). In addition, expression of rpoS has also been reported to be influenced by a small noncoding RNA, B. burgdorferi DsrA (DsrA Bb ); its chaperone, Hfq (40,41); and a putative RNA-binding protein, BB0184 (42)(43)(44)(45)(46)(47).…”