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Coupled induction of prophage and virulence factors during tick transmission of the Lyme disease spirochete

ABSTRACT: Lyme disease spirochetes must induce RpoS-dependent genes during tick feeding to prepare for host infection. Previous work in our lab identified bbd18 as a negative regulator of RpoS, but inactivation of bbd18 in wild-type spirochetes was never achieved. In the current study we generated an inducible bbd18 gene at the endogenous plasmid locus and demonstrated the essential nature of BBD18 for viability of wild-type spirochetes in vitro and at a unique point in vivo. Transcriptomic analyses demonstrated global induction of RpoS and RpoS-dependent genes following BBD18 depletion, culminating in spirochete lysis. Plasmid prophage genes were also induced and phage particles were detected in lysed culture supernatants, suggesting that RpoS regulates phage lysis-lysogeny decisions. The absolute requirement for BBD18 persisted following displacement of the entire set of cp32 plasmid prophages but could be circumvented by deletion of rpoS. This is the first report of a mechanistic link between endogenous transducing prophages and the RpoS-dependent adaptive response of the Lyme disease spirochete.

ORGANISM(S): Borreliella burgdorferi B31

PROVIDER: GSE207123 | GEO | 2022/12/12

REPOSITORIES: GEO

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Project description:The alternative sigma factor RpoS plays a central role in the critical host-adaptive response of the Lyme disease spirochete, Borrelia burgdorferi. We previously identified bbd18 as a negative regulator of RpoS but could not inactivate bbd18 in wild-type spirochetes. In the current study we employed an inducible bbd18 gene to demonstrate the essential nature of BBD18 for viability of wild-type spirochete viability in vitro and at a unique point in vivo. Transcriptomic analyses of BBD18 depleted cells demonstrated global induction of RpoS-dependent genes prior to lysis, with the absolute requirement for BBD18, both in vitro and in vivo, circumvented by deletion of rpoS. The increased expression of plasmid prophage genes and the presence of phage particles in the supernatants of lysing cultures indicate that RpoS regulates phage lysis-lysogeny decisions. Through this work we identify a mechanistic link between endogenous transducing prophages and the RpoS-dependent adaptive response of the Lyme disease spirochete. The alternative sigma factor RpoS plays a central role in the critical host-adaptive response of the Lyme disease spirochete, Borrelia burgdorferi. We previously identified bbd18 as a negative regulator of RpoS but could not inactivate bbd18 in wild-type spirochetes. In the current study we employed an inducible bbd18 gene to demonstrate the essential nature of BBD18 for viability of wild-type spirochete viability in vitro and at a unique point in vivo. Transcriptomic analyses of BBD18 depleted cells demonstrated global induction of RpoS-dependent genes prior to lysis, with the absolute requirement for BBD18, both in vitro and in vivo, circumvented by deletion of rpoS. The increased expression of plasmid prophage genes and the presence of phage particles in the supernatants of lysing cultures indicate that RpoS regulates phage lysis-lysogeny decisions. Through this work we identify a mechanistic link between endogenous transducing prophages and the RpoS-dependent adaptive response of the Lyme disease spirochete.

Project description:Spirochetes are long, thin, motile, helical or flat wave bacteria that are unique among the prokaryotes by having flagella or axial filaments confined to an internal periplasmic space. These flagella are complex organelles that can play major roles in bacterial pathogenicity and are used as propellers allowing bacteria to move through liquids, viscous environments or along surfaces. While most bacteria species use transcriptional regulatory cascades to regulate the synthesis and assembly of their flagella, spirochetes employ an unusual post-transcriptional mechanism. Using next generation sequencing, we characterized a natural mutant of the relapsing fever spirochete Borrelia hermsii lacking the flagellar export apparatus protein FliH. The mutant was non-motile, uncoiled and straight compared to the wild-type spirochetes. The B. hermsii fliH mutant produced only a residual amount of the major flagellin protein FlaB, which was correlated with a reduced number of periplasmic flagella. The amounts of flaB transcript were comparable in the fliH mutant and the wild-type strain. The synthesis of FlaB, the motility and the infectivity of the fliH mutant were rescued by trans-complementation. This report reveals a new function for FliH, and we propose that this regulator of the flagellar export apparatus influences the post-transcriptional processing of the flagella, motility and virulence of the relapsing fever spirochete Borrelia hermsii. Spirochetes are bacteria characterized in part by rotating periplasmic flagella that impart their flat-wave morphology and motility. While other bacteria rely on a transcriptional cascade to regulate the expression of motility genes, spirochetes employ posttranscriptional mechanism(s) that are only partially known. In the present study, we characterize a non-motile mutant of the relapsing fever spirochete Borrelia hermsii that was straight, non-motile and deficient in flagella. We used next generation DNA sequencing of the mutant’s genome, which when compared to the wild-type genome identified a 142 bp deletion in the chromosomal gene encoding the flagellar export apparatus protein FliH. Immunoblot and transcriptome analyses showed that the mutant phenotype was linked to the posttranscriptional deficiency in the synthesis of the major flagellar filament core protein FlaB. The turnover of the residual pool of FlaB produced by the fliH mutant was comparable to the wild-type spirochete while the amount of FlaA was similar to the wild-type level. The non-motile mutant was not infectious in mice and its inoculation did not induce an antibody response. Trans-complementation of the mutant with an intact fliH gene restored the synthesis of FlaB, a normal morphology, motility and infectivity in mice. Therefore, we propose that the flagellar export apparatus protein regulates motility of B. hermsii at the posttranscriptional level by influencing the synthesis of FlaB. Borrelia hermsii wild type vs. motility mutant

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Coupled induction of prophage and virulence factors during tick transmission of the Lyme disease spirochete

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