Study of the Response Regulator Rrp1 Reveals Its Regulatory Role in Chitobiose Utilization and Virulence of Borrelia burgdorferi

Abstract

cLife cycle alternation between arthropod and mammals forces the Lyme disease spirochete, Borrelia burgdorferi, to adapt to different host milieus by utilizing diverse carbohydrates. Glycerol and chitobiose are abundantly present in the Ixodes tick. B. burgdorferi can utilize glycerol as a carbohydrate source for glycolysis and chitobiose to produce N-acetylglucosamine (GlcNAc), a key component of the bacterial cell wall. A recent study reported that Rrp1, a response regulator that synthesizes cyclic diguanylate (c-di-GMP), governs glycerol utilization in B. burgdorferi. In this report, we found that the rrp1 mutant had growth defects and formed membrane blebs that led to cell lysis when GlcNAc was replaced by chitobiose in the growth medium. The gene chbC encodes a key chitobiose transporter of B. burgdorferi. We found that the expression level of chbC was significantly repressed in the mutant and that constitutive expression of chbC in the mutant successfully rescued the growth defect, indicating a regulatory role of Rrp1 in chitobiose uptake. Immunoblotting and transcriptional studies revealed that Rrp1 is required for the activation of bosR and rpoS and that its impact on chbC is most likely mediated by the BosR-RpoS regulatory pathway. Tick-mouse infection studies showed that although the rrp1 mutant failed to establish infection in mice via tick bite, exogenous supplementation of GlcNAc into unfed ticks partially rescued the infection. The finding reported here provides us with new insight into the regulatory role of Rrp1 in carbohydrate utilization and virulence of B. burgdorferi.

DhhP, a Cyclic di-AMP Phosphodiesterase of Borrelia burgdorferi, Is Essential for Cell Growth and Virulence

“…Since a method to assess the level of Rrp2 phosphorylation within the cell is lacking, a potential impact of DhhP on Rrp2 phosphorylation could not be examined. Therefore, we focused on regulation of BosR (43,57,66). Similar to what was seen with the levels of RpoS, the dhhP mutant failed to induce BosR production in the absence of IPTG, indicating that the loss of OspC and RpoS in the dhhP mutant was due to a defect in BosR production (Fig.…”

“…Amazingly, B. burgdorferi accomplishes these dramatic processes with its streamlined genome and limited regulatory repertoire (32). For example, in contrast to many bacteria that have numerous c-di-GMP signaling systems (33)(34)(35)(36), B. burgdorferi has only one c-di-GMP synthase (BB0419, diguanylate cyclase), and it plays an essential role in spirochetal survival in ticks as well as modulating B. burgdorferi motility and mammalian infection (37)(38)(39)(40)(41)(42)(43).…”

Cyclic Di-GMP Receptor PlzA Controls Virulence Gene Expression through RpoS in Borrelia burgdorferi

“…Glycerol is produced by some insects as well as arthropods as a cryoprotective molecule (28), whereas chitobiose (derived from chitin), a major component of the tick cuticle, is an important source of N-acetylglucosamine for cell wall synthesis of B. burgdorferi (29)(30)(31). It was found that expression of the glycerol uptake/metabolism operon glpFKD, a chitobiose transporter gene (chbC) (30,31), and several glucosamine metabolism genes is governed by Rrp1 (23,25,32). Furthermore, constitutive expression of glpFKD in the rrp1 mutant or supplementing N-acetylglucosamine in tick midguts partially rescued the rrp1 mutant's survival in ticks or its transmission to the mammalian host (23,32).…”

“…It was found that expression of the glycerol uptake/metabolism operon glpFKD, a chitobiose transporter gene (chbC) (30,31), and several glucosamine metabolism genes is governed by Rrp1 (23,25,32). Furthermore, constitutive expression of glpFKD in the rrp1 mutant or supplementing N-acetylglucosamine in tick midguts partially rescued the rrp1 mutant's survival in ticks or its transmission to the mammalian host (23,32).…”

Insight into the Dual Functions of Bacterial Enhancer-Binding Protein Rrp2 of Borrelia burgdorferi

“…RpoS, functioning as a global regulator, further controls the expression of numerous genes important for the enzootic cycle of B. burgdorferi (for a review, see references 2, 3, and 9). Since the first discovery of this pathway, additional factors, including BosR (10)(11)(12), BadR (13,14), DsrA (15), Rrp1 (16)(17)(18), and the posttranscriptional regulation of rpoS (19), have been identified.…”