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Function of the Borrelia burgdorferi FtsH Homolog Is Essential for Viability both In Vitro and In Vivo and Independent of HflK/C.

ABSTRACT:

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In many bacteria, the FtsH protease and its modulators, HflK and HflC, form a large protein complex that contributes to both membrane protein quality control and regulation of the cellular response to environmental stress. Both activities are crucial to the Lyme disease pathogen Borrelia burgdorferi, which depends on membrane functions, such as motility, protein transport, and cell signaling, to respond to rapid changes in its environment. Using an inducible system, we demonstrate that FtsH production is essential for both mouse and tick infectivity and for in vitro growth of B. burgdorferi FtsH depletion in B. burgdorferi cells resulted in membrane deformation and cell death. Overproduction of the protease did not have any detectable adverse effects on B. burgdorferi growth in vitro, suggesting that excess FtsH does not proteolytically overwhelm its substrates. In contrast, we did not observe any phenotype for cells lacking the protease modulators HflK and HflC (?HflK/C), although we examined morphology, growth rate, growth under stress conditions, and the complete mouse-tick infectious cycle. Our results demonstrate that FtsH provides an essential function in the life cycle of the obligate pathogen B. burgdorferi but that HflK and HflC do not detectably affect FtsH function.

Importance

Lyme disease is caused by Borrelia burgdorferi, which is maintained in nature in an infectious cycle alternating between small mammals and Ixodes ticks. B. burgdorferi produces specific membrane proteins to successfully infect and persist in these diverse organisms. We hypothesized that B. burgdorferi has a specific mechanism to ensure that membrane proteins are properly folded and biologically active when needed and removed if improperly folded or dysfunctional. Our experiments demonstrate that FtsH, a protease that fulfills this role in other microorganisms, is essential to B. burgdorferi viability. Cells depleted of FtsH do not survive in laboratory culture medium and cannot colonize mice or ticks, revealing an absolute requirement for this protease. However, the loss of two potential modulators of FtsH activity, HflK and HflC, does not detectably affect B. burgdorferi physiology. Our results provide the groundwork for the identification of FtsH substrates that are critical for the bacterium's viability.

SUBMITTER: Chu CY

PROVIDER: S-EPMC4850261 | biostudies-literature | 2016 Apr

REPOSITORIES: biostudies-literature

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Publications

Function of the Borrelia burgdorferi FtsH Homolog Is Essential for Viability both In Vitro and In Vivo and Independent of HflK/C.

Chu Chen-Yi CY Stewart Philip E PE Bestor Aaron A Hansen Bryan B Lin Tao T Gao Lihui L Norris Steven J SJ Rosa Patricia A PA

mBio 20160419 2

<h4>Unlabelled</h4>In many bacteria, the FtsH protease and its modulators, HflK and HflC, form a large protein complex that contributes to both membrane protein quality control and regulation of the cellular response to environmental stress. Both activities are crucial to the Lyme disease pathogen Borrelia burgdorferi, which depends on membrane functions, such as motility, protein transport, and cell signaling, to respond to rapid changes in its environment. Using an inducible system, we demonst ...[more]

PMID: 27094329

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Project description:Borrelia burgdorferi is an extreme amino acid (AA) auxotroph whose genome encodes few free AA transporters and an elaborate oligopeptide transport system (B. burgdorferi Opp [BbOpp]). BbOpp consists of five oligopeptide-binding proteins (OBPs), two heterodimeric permeases, and a heterodimeric nucleotide-binding domain (NBD). Homology modeling based on the crystal structure of liganded BbOppA4 revealed that each OBP likely binds a distinct range of peptides. Transcriptional analyses demonstrated that the OBPs are differentially and independently regulated whereas the permeases and NBDs are constitutively expressed. A conditional NBD mutant failed to divide in the absence of inducer and replicated in an IPTG (isopropyl-?-d-thiogalactopyranoside) concentration-dependent manner. NBD mutants grown without IPTG exhibited an elongated morphotype lacking division septa, often with flattening at the cell center due to the absence of flagellar filaments. Following cultivation in dialysis membrane chambers, NBD mutants recovered from rats not receiving IPTG also displayed an elongated morphotype. The NBD mutant was avirulent by needle inoculation, but infectivity was partially restored by oral administration of IPTG to infected mice. We conclude that peptides are a major source of AAs for B. burgdorferi both in vitro and in vivo and that peptide uptake is essential for regulation of morphogenesis, cell division, and virulence.IMPORTANCEBorrelia burgdorferi, the causative agent of Lyme disease, is an extreme amino acid (AA) auxotroph with a limited repertoire of annotated single-AA transporters. A major issue is how the spirochete meets its AA requirements as it transits between its arthropod vector and mammalian reservoir. While previous studies have confirmed that the B. burgdorferi oligopeptide transport (opp) system is capable of importing peptides, the importance of the system for viability and pathogenesis has not been established. Here, we evaluated the opp system structurally and transcriptionally to elucidate its ability to import a wide range of peptides during the spirochete's enzootic cycle. Additionally, using a novel mutagenesis strategy to abrogate opp transporter function, we demonstrated that peptide uptake is essential for bacterial viability, morphogenesis, and infectivity. Our studies revealed a novel link between borrelial physiology and virulence and suggest that peptide uptake serves an intracellular signaling function regulating morphogenesis and division.

Dataset Information

Function of the Borrelia burgdorferi FtsH Homolog Is Essential for Viability both In Vitro and In Vivo and Independent of HflK/C.

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Publications

Function of the Borrelia burgdorferi FtsH Homolog Is Essential for Viability both In Vitro and In Vivo and Independent of HflK/C.

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