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The two-component system ChrSA is crucial for heme tolerance and interferes with HrrSA in heme-dependent gene regulation in Corynebacterium glutamicum

ABSTRACT: We recently showed that the two-component system (TCS) HrrSA plays a central role in the control of heme homeostasis in the Gram-positive soil bacterium Corynebacterium glutamicum. Here, we characterized the function of another TCS of this organism, ChrSA, which exhibits significant sequence similarity to HrrSA, and provide evidence for cross-regulation of the two systems. In this study ChrSA was shown to be crucial for heme resistance of C. glutamicum by activation of the putative heme-detoxifying ABC-transporter HrtBA in the presence of heme. Deletion of either hrtBA or chrSA resulted in a strongly increased sensitivity towards heme. DNA microarray analysis and gel retardation assays with the purified response regulator ChrA provided evidence for ChrA being a repressor of the heme biosynthesis operon hemAC and hemH and an activator of the ctaE-qcrCAB operon, encoding subunits of the cytochrome bc1-aa3 supercomplex of the respiratory chain. The heme oxygenase gene, hmuO, showed a strongly decreased mRNA level in the ΔchrSA mutant, but no significant binding of ChrA was observed in vitro. Promoter fusion studies of PchrSA with eyfp indicated positive autoregulation of the chrSA operon in the presence of heme. Interestingly, ChrA was also shown to bind to the hrrA promoter and to repress transcription of the paralog response regulator, suggesting a close link between HrrSA and ChrSA. Mutational analysis and in silico prediction resulted in the deduction of a 16-bp weakly conserved inverted repeat as consensus DNA-binding motif of ChrA. Altogether, the present study emphasizes ChrSA as a second TCS, besides HrrSA, involved in heme-dependent gene regulation in C. glutamicum.

ORGANISM(S): Corynebacterium glutamicum ATCC 13032

PROVIDER: GSE37327 | GEO | 2012/10/31

SECONDARY ACCESSION(S): PRJNA159583

REPOSITORIES: GEO

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Project description:We recently showed that the two-component system (TCS) HrrSA plays a central role in the control of heme homeostasis in the Gram-positive soil bacterium Corynebacterium glutamicum. Here, we characterized the function of another TCS of this organism, ChrSA, which exhibits significant sequence similarity to HrrSA, and provide evidence for cross-regulation of the two systems. In this study ChrSA was shown to be crucial for heme resistance of C. glutamicum by activation of the putative heme-detoxifying ABC-transporter HrtBA in the presence of heme. Deletion of either hrtBA or chrSA resulted in a strongly increased sensitivity towards heme. DNA microarray analysis and gel retardation assays with the purified response regulator ChrA provided evidence for ChrA being a repressor of the heme biosynthesis operon hemAC and hemH and an activator of the ctaE-qcrCAB operon, encoding subunits of the cytochrome bc1-aa3 supercomplex of the respiratory chain. The heme oxygenase gene, hmuO, showed a strongly decreased mRNA level in the M-NM-^TchrSA mutant, but no significant binding of ChrA was observed in vitro. Promoter fusion studies of PchrSA with eyfp indicated positive autoregulation of the chrSA operon in the presence of heme. Interestingly, ChrA was also shown to bind to the hrrA promoter and to repress transcription of the paralog response regulator, suggesting a close link between HrrSA and ChrSA. Mutational analysis and in silico prediction resulted in the deduction of a 16-bp weakly conserved inverted repeat as consensus DNA-binding motif of ChrA. Altogether, the present study emphasizes ChrSA as a second TCS, besides HrrSA, involved in heme-dependent gene regulation in C. glutamicum. To identify the influence of ChrSA on global gene expression , DNA microarray analyses were performed with the M-NM-^TchrSA mutant compared to C. glutamicum wild type. For this purpose RNA was isolated from exponentially growing cells cultivated in CgXII minimal medium with 4% glucose and either 2.5 M-BM-5M FeSO4 or 2.5 M-BM-5M hemin as iron source. Three biological replicates were performed.

Project description:The response regulator HrrA belonging to the HrrSA two-component system (previously named CgtSR11) is known to be repressed by the global iron-dependent regulator DtxR in Corynebacterium glutamicum. Sequence analysis indicated an involvement of the HrrSA system in heme-dependent gene expression. Growth experiments revealed that the non-pathogenic soil bacterium C. glutamicum is able to use hemin or hemoglobin as sole iron source. In DNA microarray analyses a putative operon encoding the hemin-binding protein HtaA and the putative hemin ABC transporter HmuTUV showed a strong upregulation in heme-grown cells. Deletion of the hmu operon clearly affects heme utilization, but does not completely abolish growth on heme or hemoglobin. As a central part of this study, we investigated the regulon of the response regulator HrrA via comparative transcriptome analysis of a hrrA deletion mutant and C. glutamicum wild type in combination with DNA-protein interaction studies with purified HrrA protein. Our data provide evidence for a heme-dependent transcriptional activation of heme oxygenase (hmuO), an enzyme involved in the utilization of heme as iron source. Besides hmuO, HrrA was shown to activate the expression of heme-containing components of the respiratory chain, namely ctaD and the ctaE-qcrCAB operon encoding subunits I and III of cytochrome aa3 oxidase and three subunits of the cytochrome bc1 complex. Furthermore, HrrA represses almost all genes involved in heme biosynthesis, including glutamyl-tRNA reductase (hemA), uroporphyrinogen decarboxylase (hemE), and ferrochelatase (hemH). Thus, our data clearly emphasize a central role of the HrrSA system in the control of heme homeostasis in C. glutamicum. Three biological replicates of each experiment were performed. Experiment 1: Transcriptome comparison of wild type grown und FeSO4 or heme as iron source; Exp. 2: WT vs. hrrA deletion mutant grown on FeSO4; Exp. 3: WT vs. hrrA mutant grown on heme. For analysis via DNA microarraysose RNA was isolated from exponentially growing cells cultivated in CgXII medium containing glucose as carbon source and either 2.5 uM FeSO4 or 2.5 uM heme as iron source.

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The two-component system ChrSA is crucial for heme tolerance and interferes with HrrSA in heme-dependent gene regulation in Corynebacterium glutamicum

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