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Vajrala N, Sayavedra-Soto LA, Bottomley PJ, Arp DJ. Role of a Fur homolog in iron metabolism in Nitrosomonas europaea. BMC Microbiol 2011; 11:37. [PMID: 21338516 PMCID: PMC3050691 DOI: 10.1186/1471-2180-11-37] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2010] [Accepted: 02/21/2011] [Indexed: 11/24/2022] Open
Abstract
Background In response to environmental iron concentrations, many bacteria coordinately regulate transcription of genes involved in iron acquisition via the ferric uptake regulation (Fur) system. The genome of Nitrosomonas europaea, an ammonia-oxidizing bacterium, carries three genes (NE0616, NE0730 and NE1722) encoding proteins belonging to Fur family. Results Of the three N. europaea fur homologs, only the Fur homolog encoded by gene NE0616 complemented the Escherichia coli H1780 fur mutant. A N. europaea fur:kanP mutant strain was created by insertion of kanamycin-resistance cassette in the promoter region of NE0616 fur homolog. The total cellular iron contents of the fur:kanP mutant strain increased by 1.5-fold compared to wild type when grown in Fe-replete media. Relative to the wild type, the fur:kanP mutant exhibited increased sensitivity to iron at or above 500 μM concentrations. Unlike the wild type, the fur:kanP mutant was capable of utilizing iron-bound ferrioxamine without any lag phase and showed over expression of several outer membrane TonB-dependent receptor proteins irrespective of Fe availability. Conclusions Our studies have clearly indicated a role in Fe regulation by the Fur protein encoded by N. europaea NE0616 gene. Additional studies are required to fully delineate role of this fur homolog.
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Affiliation(s)
- Neeraja Vajrala
- Department of Botany and Plant Pathology, 2082 Cordley, Oregon State University, Corvallis, OR 97331, USA
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Abstract
Both the essentiality and toxicity of transition metals are exploited as part of mammalian immune defenses against bacterial infection. Salmonella serovars continue to cause serious medical and veterinary problems worldwide and detecting deficiency and excess of different metal ions (such as copper, iron, zinc, manganese, nickel, and cobalt) is fundamental to their virulence. This involves multiple DNA-binding metal-responsive transcription factors that discriminate between elements and trigger expression of genes that mediate appropriate responses to metal fluxes. This review focuses on the metal stresses encountered by Salmonella during infection and the roles of the different metal-sensing regulatory proteins and their target genes in adapting to these changing metal levels. Current knowledge regarding the mechanisms of metal-regulated gene expression and the structural features of sensory metal binding sites are described. In addition, the principles governing the ability of the different sensors to detect specific metals within a cell to control cytosolic metal levels are also discussed. These proteins represent potential targets for the development of new therapeutic approaches.
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Ferraz LFC, Verde LCL, Vicentini R, Felício AP, Ribeiro ML, Alexandrino F, Novo MTM, Garcia O, Rigden DJ, Ottoboni LMM. Ferric iron uptake genes are differentially expressed in the presence of copper sulfides in Acidithiobacillus ferrooxidans strain LR. Antonie van Leeuwenhoek 2010; 99:609-17. [PMID: 21132364 DOI: 10.1007/s10482-010-9533-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/20/2010] [Accepted: 11/19/2010] [Indexed: 10/18/2022]
Abstract
Acidithiobacillus ferrooxidans is one of the most widely used microorganisms in bioleaching operations to recover copper from low-grade copper sulfide ores. This work aimed to investigate the relative expression of genes related to the iron uptake system when A. ferrooxidans LR was maintained in contact with chalcopyrite or bornite as the sole energy source. Real-time quantitative PCR analysis revealed that the presence of bornite had no effect on the expression of seven genes related to the siderophore-mediated Fe(III) uptake system, while in the presence of chalcopyrite the expression of the genes was up-regulated. Bioinformatic analysis of the genomic region where these genes were found revealed the existence of three new putative DNA-binding sequences for the ferric iron uptake transcriptional regulator (Fur). Electrophoretic mobility shift assays demonstrated that a purified A. ferrooxidans His-tagged Fur protein was able to bind in vitro to each of these putative Fur boxes, suggesting that Fur regulated the expression of these genes. The expression of fur and two known Fur-regulated genes, mntH and dsrK, was also investigated in the presence of chalcopyrite. While the expression of fur and mntH was up-regulated, the expression of dsrK was down-regulated. The low amount of ferrous iron in the medium was probably responsible for the up-regulation of fur and the genes related to the siderophore-mediated Fe(III) uptake system when A. ferrooxidans LR was kept in the presence of chalcopyrite. A homology model of the A. ferrooxidans Fur was constructed and revealed that the putative DNA-binding surface presents conserved positively charged residues, supporting a previously suggested mode of interaction with DNA. The up-regulation of fur and the siderophore-mediated Fe(III) uptake genes, and the down-regulation of dsrK suggest that in the presence of chalcopyrite Fur acts as a transcription inducer and repressor.
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Affiliation(s)
- Lúcio F C Ferraz
- Centro de Biologia Molecular e Engenharia Genética, Universidade Estadual de Campinas, Campinas, SP 13083-875, Brazil
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Bruno-Bárcena JM, Azcárate-Peril MA, Hassan HM. Role of antioxidant enzymes in bacterial resistance to organic acids. Appl Environ Microbiol 2010; 76:2747-53. [PMID: 20305033 PMCID: PMC2863438 DOI: 10.1128/aem.02718-09] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2009] [Accepted: 03/08/2010] [Indexed: 11/20/2022] Open
Abstract
Growth in aerobic environments has been shown to generate reactive oxygen species (ROS) and to cause oxidative stress in most organisms. Antioxidant enzymes (i.e., superoxide dismutases and hydroperoxidases) and DNA repair mechanisms provide protection against ROS. Acid stress has been shown to be associated with the induction of Mn superoxide dismutase (MnSOD) in Lactococcus lactis and Staphylococcus aureus. However, the relationship between acid stress and oxidative stress is not well understood. In the present study, we showed that mutations in the gene coding for MnSOD (sodA) increased the toxicity of lactic acid at pH 3.5 in Streptococcus thermophilus. The inclusion of the iron chelators 2,2'-dipyridyl (DIP), diethienetriamine-pentaacetic acid (DTPA), and O-phenanthroline (O-Phe) provided partial protection against 330 mM lactic acid at pH 3.5. The results suggested that acid stress triggers an iron-mediated oxidative stress that can be ameliorated by MnSOD and iron chelators. These findings were further validated in Escherichia coli strains lacking both MnSOD and iron SOD (FeSOD) but expressing a heterologous MnSOD from S. thermophilus. We also found that, in E. coli, FeSOD did not provide the same protection afforded by MnSOD and that hydroperoxidases are equally important in protecting the cells against acid stress. These findings may explain the ability of some microorganisms to survive better in acidified environments, as in acid foods, during fermentation and accumulation of lactic acid or during passage through the low pH of the stomach.
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Affiliation(s)
- Jose M. Bruno-Bárcena
- Department of Microbiology, Golden Leaf Bio-Manufacturing Training and Education Center, North Carolina State University, Raleigh, North Carolina 27695-7615, Department of Cell and Molecular Physiology, School of Medicine, University of North Carolina, Chapel Hill, North Carolina 27599-7545
| | - M. Andrea Azcárate-Peril
- Department of Microbiology, Golden Leaf Bio-Manufacturing Training and Education Center, North Carolina State University, Raleigh, North Carolina 27695-7615, Department of Cell and Molecular Physiology, School of Medicine, University of North Carolina, Chapel Hill, North Carolina 27599-7545
| | - Hosni M. Hassan
- Department of Microbiology, Golden Leaf Bio-Manufacturing Training and Education Center, North Carolina State University, Raleigh, North Carolina 27695-7615, Department of Cell and Molecular Physiology, School of Medicine, University of North Carolina, Chapel Hill, North Carolina 27599-7545
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Construction of recombinant attenuated Salmonella enterica serovar typhimurium vaccine vector strains for safety in newborn and infant mice. CLINICAL AND VACCINE IMMUNOLOGY : CVI 2010; 17:354-62. [PMID: 20053874 DOI: 10.1128/cvi.00412-09] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Recombinant bacterial vaccines must be safe, efficacious, and well tolerated, especially when administered to newborns and infants to prevent diseases of early childhood. Many means of attenuation have been shown to render vaccine strains susceptible to host defenses or unable to colonize lymphoid tissue effectively, thus decreasing their immunogenicity. We have constructed recombinant attenuated Salmonella vaccine strains that display high levels of attenuation while retaining the ability to induce high levels of immunogenicity and are well tolerated in high doses when administered to infant mice as young as 24 h old. The strains contain three means of regulated delayed attenuation, as well as a constellation of additional mutations that aid in enhancing safety, regulate antigen expression, and reduce disease symptoms commonly associated with Salmonella infection. The vaccine strains are well tolerated when orally administered to infant mice 24 h old at doses as high as 3.5 x 10(8) CFU.
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56
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Lee JS, Choe YH, Lee JH, Lee HJ, Lee JH, Choi YO. Helicobacter pylori urease activity is influenced by ferric uptake regulator. Yonsei Med J 2010; 51:39-44. [PMID: 20046512 PMCID: PMC2799959 DOI: 10.3349/ymj.2010.51.1.39] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/19/2009] [Revised: 05/06/2009] [Accepted: 05/06/2009] [Indexed: 01/22/2023] Open
Abstract
PURPOSE The role of the Ferric Uptake Regulator (FUR) in the acid resistance of Helicobacter pylori (H. pylori) has been thought to be independent of urease. However, we demonstrated in this study that Fur influences urease activity. MATERIALS AND METHODS A fur knockout mutant of H. pylori was constructed by replacing the Fur gene with a kanamycin resistant marker gene. The wild-type H. pylori and fur mutant were compared for survival. The integrity of the inner membrane of the bacteria was evaluated by confocal microscopy using membrane-permeant and -impermeant fluorescent DNA probes. Urease activity of intact H. pylori was measured between pH 3 and 8. Real time PCR of both strains was performed for urease genes including ureI, ureE, ureF, ureG, and ureH. RESULTS The fur deletion affected the survival of H. pylori at pH 4. The urease activity curve of the intact fur mutant showed the same shape as the wild-type but was 3-fold lower than the wild-type at a pH of less than 5. Real time PCR revealed that the expression of all genes was consistently down-regulated in the fur mutant. CONCLUSION The results of this study showed that fur appears to be involved in acid resistant H. pylori urease activity.
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Affiliation(s)
- Jong Seung Lee
- Department of Pediatrics, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea
| | - Yon Ho Choe
- Department of Pediatrics, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea
| | - Ji Hyuk Lee
- Department of Pediatrics, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea
| | - Hye Jin Lee
- Department of Pediatrics, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea
| | - Jee Hyun Lee
- Department of Pediatrics, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea
| | - Young Ok Choi
- Department of Pediatrics, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea
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Sheikh MA, Taylor GL. Crystal structure of the Vibrio cholerae ferric uptake regulator (Fur) reveals insights into metal co-ordination. Mol Microbiol 2009; 72:1208-20. [PMID: 19400801 DOI: 10.1111/j.1365-2958.2009.06718.x] [Citation(s) in RCA: 107] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The ferric uptake regulator (Fur) is a metal-dependent DNA-binding protein that acts as both a repressor and an activator of numerous genes involved in maintaining iron homeostasis in bacteria. It has also been demonstrated in Vibrio cholerae that Fur plays an additional role in pathogenesis, opening up the potential of Fur as a drug target for cholera. Here we present the crystal structure of V. cholerae Fur that reveals a very different orientation of the DNA-binding domains compared with that observed in Pseudomonas aeruginosa Fur. Each monomer of the dimeric Fur protein contains two metal binding sites occupied by zinc in the crystal structure. In the P. aeruginosa study these were designated as the regulatory site (Zn1) and structural site (Zn2). This V. cholerae Fur study, together with studies on Fur homologues and paralogues, suggests that in fact the Zn2 site is the regulatory iron binding site and the Zn1 site plays an auxiliary role. There is no evidence of metal binding to the cysteines that are conserved in many Fur homologues, including Escherichia coli Fur. An analysis of the metal binding properties shows that V. cholerae Fur can be activated by a range of divalent metals.
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Affiliation(s)
- Md Arif Sheikh
- Centre for Biomolecular Sciences, University of St Andrews, St Andrews, Fife KY16 9ST, UK
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58
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This is not your mother's repressor: the complex role of fur in pathogenesis. Infect Immun 2009; 77:2590-601. [PMID: 19364842 DOI: 10.1128/iai.00116-09] [Citation(s) in RCA: 166] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
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Salmonella enterica serovar typhimurium strains with regulated delayed attenuation in vivo. Infect Immun 2008; 77:1071-82. [PMID: 19103774 DOI: 10.1128/iai.00693-08] [Citation(s) in RCA: 126] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Recombinant bacterial vaccines must be fully attenuated for animal or human hosts to avoid inducing disease symptoms while exhibiting a high degree of immunogenicity. Unfortunately, many well-studied means for attenuating Salmonella render strains more susceptible to host defense stresses encountered following oral vaccination than wild-type virulent strains and/or impair their ability to effectively colonize the gut-associated and internal lymphoid tissues. This thus impairs the ability of recombinant vaccines to serve as factories to produce recombinant antigens to induce the desired protective immunity. To address these problems, we designed strains that display features of wild-type virulent strains of Salmonella at the time of immunization to enable strains first to effectively colonize lymphoid tissues and then to exhibit a regulated delayed attenuation in vivo to preclude inducing disease symptoms. We recently described one means to achieve this based on a reversible smooth-rough synthesis of lipopolysaccharide O antigen. We report here a second means to achieve regulated delayed attenuation in vivo that is based on the substitution of a tightly regulated araC P(BAD) cassette for the promoters of the fur, crp, phoPQ, and rpoS genes such that expression of these genes is dependent on arabinose provided during growth. Thus, following colonization of lymphoid tissues, the Fur, Crp, PhoPQ, and/or RpoS proteins cease to be synthesized due to the absence of arabinose such that attenuation is gradually manifest in vivo to preclude induction of diseases symptoms. Means for achieving regulated delayed attenuation can be combined with other mutations, which together may yield safe efficacious recombinant attenuated Salmonella vaccines.
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60
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Raza W, Wu H, Shah MAA, Shen Q. Retracted: A catechol type siderophore, bacillibactin: biosynthesis, regulation and transport in Bacillus subtilis. J Basic Microbiol 2008; 48. [PMID: 18785660 DOI: 10.1002/jobm.200800097] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Retraction: The following article from the Journal of Basic Microbiology, "A catechol type siderophore, bacillibactin: biosynthesis, regulation and transport in Bacillus subtilis" by Waseem Raza, Hongsheng Wu, Muhammad Ali Abdullah Shah and Qirong Shen, published online on 11 September 2008 in Wiley InterScience (www.interscience.wiley.com), has been retracted by agreement between the authors, the journal Editor-in-Chief, Erika Kothe, and the publisher Wiley-VCH. The retraction has been agreed due to substantial overlap of the content of this article with previously published articles in other journals.The Journal of Basic Microbiology apologises to our readership.
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Affiliation(s)
- Waseem Raza
- College of Resource and Environmental Sciences, Nanjing Agriculture University, Nanjing, China
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61
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Yuhara S, Komatsu H, Goto H, Ohtsubo Y, Nagata Y, Tsuda M. Pleiotropic roles of iron-responsive transcriptional regulator Fur in Burkholderia multivorans. MICROBIOLOGY-SGM 2008; 154:1763-1774. [PMID: 18524931 DOI: 10.1099/mic.0.2007/015537-0] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The fur (ferric uptake regulator) gene of Burkholderia multivorans ATCC 17616 was identified by transposon mutagenesis analysis. The fur deletion mutant of strain ATCC 17616 (i) constitutively produced siderophores, (ii) was more sensitive to reactive oxygen species (ROS) than the wild-type strain, (iii) showed lower superoxide dismutase and catalase activities than the wild-type strain, (iv) was unable to grow on M9 minimal agar plates containing several substrates that can be used as sole carbon sources by the wild-type strain, and (v) was hypersensitive to nitrite and nitric oxide under microaerobic and aerobic conditions, respectively. These results clearly indicate that the Fur protein in strain ATCC 17616 plays pleiotropic roles in iron homeostasis, removal and/or resistance to ROS and nitrosative stress, and energy metabolism. Furthermore, employment of an in vivo Fur titration assay system led to the isolation from the ATCC 17616 genome of 13 Fur-binding DNA regions, and a subsequent electrophoretic mobility-shift assay confirmed the direct binding of Fur protein to all of these DNA regions. Transcriptional analysis of the genes located just downstream of the Fur-binding sites demonstrated that Fur acts as a repressor for these genes. Nine of the 13 regions were presumed to be involved in the acquisition and utilization of iron.
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Affiliation(s)
- Satoshi Yuhara
- Department of Environmental Life Sciences, Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Sendai 980-8577, Japan
| | - Harunobu Komatsu
- Department of Environmental Life Sciences, Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Sendai 980-8577, Japan
| | - Hiroyuki Goto
- Department of Environmental Life Sciences, Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Sendai 980-8577, Japan
| | - Yoshiyuki Ohtsubo
- Department of Environmental Life Sciences, Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Sendai 980-8577, Japan
| | - Yuji Nagata
- Department of Environmental Life Sciences, Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Sendai 980-8577, Japan
| | - Masataka Tsuda
- Department of Environmental Life Sciences, Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Sendai 980-8577, Japan
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Sevilla E, Martin-Luna B, Vela L, Bes MT, Fillat MF, Peleato ML. Iron availability affects mcyD expression and microcystin-LR synthesis in Microcystis aeruginosa PCC7806. Environ Microbiol 2008; 10:2476-83. [DOI: 10.1111/j.1462-2920.2008.01663.x] [Citation(s) in RCA: 135] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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63
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Wang F, Cheng S, Sun K, Sun L. Molecular analysis of the fur (ferric uptake regulator) gene of a pathogenic Edwardsiella tarda strain. J Microbiol 2008; 46:350-5. [PMID: 18604507 DOI: 10.1007/s12275-008-0038-x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2008] [Accepted: 03/18/2008] [Indexed: 12/29/2022]
Abstract
The gene encoding the Edwardsiella tarda ferric uptake regulator (Fur(Et)) was cloned from a pathogenic E. tarda strain isolated from diseased fish. Fur(Et) shares 90% overall sequence identity with the Escherichia coli Fur (Fur(Ec)) and was able to complement the mutant phenotype of a fur (Ec)-defective E. coli strain. Mutational analysis indicated that C92S and C95S mutations inactivated Fur(Et) whereas E112K mutation resulted in a superactive Fur(Et) variant. Fur(Et) negatively regulated its own expression; interruption of this regulation impaired bacterial growth, altered the production of certain outer membrane proteins, and attenuated bacterial virulence.
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Affiliation(s)
- Fang Wang
- Institute of Oceanology, Chinese Academy of Sciences, Qingdao, PR China
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Subinhibitory concentrations of tetracycline affect virulence gene expression in a multi-resistant Salmonella enterica subsp. enterica serovar Typhimurium DT104. Microbes Infect 2008; 10:901-7. [DOI: 10.1016/j.micinf.2008.05.005] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2008] [Revised: 05/20/2008] [Accepted: 05/26/2008] [Indexed: 11/22/2022]
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Fur-dependent detoxification of organic acids by rpoS mutants during prolonged incubation under aerobic, phosphate starvation conditions. J Bacteriol 2008; 190:5567-75. [PMID: 18556786 DOI: 10.1128/jb.00577-08] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The activity of amino acid-dependent acid resistance systems allows Escherichia coli to survive during prolonged incubation under phosphate (P(i)) starvation conditions. We show in this work that rpoS-null mutants incubated in the absence of any amino acid survived during prolonged incubation under aerobic, P(i) starvation conditions. Whereas rpoS(+) cells incubated with glutamate excreted high levels of acetate, rpoS mutants grew on acetic acid. The characteristic metabolism of rpoS mutants required the activity of Fur (ferric uptake regulator) in order to decrease the synthesis of the small RNA RyhB that might otherwise inhibit the synthesis of iron-rich proteins. We propose that RpoS (sigma(S)) and the small RNA RyhB contribute to decrease the synthesis of iron-rich proteins required for the activity of the tricarboxylic acid (TCA) cycle, which redirects the metabolic flux toward the production of acetic acid at the onset of stationary phase in rpoS(+) cells. In contrast, Fur activity, which represses ryhB, and the lack of RpoS activity allow a substantial activity of the TCA cycle to continue in stationary phase in rpoS mutants, which decreases the production of acetic acid and, eventually, allows growth on acetic acid and P(i) excreted into the medium. These data may help explain the fact that a high frequency of E. coli rpoS mutants is found in nature.
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Acid pre-adaptation enhances virulence of Salmonella enterica serovar Typhimurium dam mutant. ACTA ACUST UNITED AC 2008; 57:358-62. [PMID: 18456425 DOI: 10.1016/j.patbio.2008.02.020] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2008] [Accepted: 02/28/2008] [Indexed: 11/21/2022]
Abstract
It is well established that success or failure of bacterial pathogens during infection relies upon its ability to overcome many lethal environments in the host such as acidity, osmolarity and bile salts. In the present study, we have studied the effects of acid adaptation on the virulence of Salmonella enterica serovar Typhimurium dam mutant. Our results indicated that LD(50) of adapted strains were lower than those of control strains. Also, the in vivo assays have shown that the development of a systemic infection is slower for control strains than for adapted strains. In addition, the number of acid-adapted mutants colonizing spleen and liver is higher than control strains. Adhesion and invasion experiments were performed in order to compare the pathogenicity of Salmonella. No significant differences were shown between pre-treated and non-adapted strains. According to these results, we report that acid adaptation of Salmonella enterica serovar Typhimurium dam mutants can increase their in vivo virulence in mice.
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JIANG HONG, GAO XUE, LI YUAN, XU ZHIKAI, WANG LIMEI, BAI XUEFAN, XUE YING. Prokaryotic expression and monoclonal antibody preparation ofMycobacterium tuberculosisferric uptake regulator B. APMIS 2008; 116:372-81. [DOI: 10.1111/j.1600-0463.2008.00975.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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Sala C, Forti F, Magnoni F, Ghisotti D. The katG mRNA of Mycobacterium tuberculosis and Mycobacterium smegmatis is processed at its 5' end and is stabilized by both a polypurine sequence and translation initiation. BMC Mol Biol 2008; 9:33. [PMID: 18394163 PMCID: PMC2358910 DOI: 10.1186/1471-2199-9-33] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2007] [Accepted: 04/04/2008] [Indexed: 11/30/2022] Open
Abstract
Background In Mycobacterium tuberculosis and in Mycobacterium smegmatis the furA-katG loci, encoding the FurA regulatory protein and the KatG catalase-peroxidase, are highly conserved. In M. tuberculosis furA-katG constitute a single operon, whereas in M. smegmatis a single mRNA covering both genes could not be found. In both species, specific 5' ends have been identified: the first one, located upstream of the furA gene, corresponds to transcription initiation from the furA promoter; the second one is the katG mRNA 5' end, located in the terminal part of furA. Results In this work we demonstrate by in vitro transcription and by RNA polymerase Chromatin immunoprecipitation that no promoter is present in the M. smegmatis region covering the latter 5' end, suggesting that it is produced by specific processing of longer transcripts. Several DNA fragments of M. tuberculosis and M. smegmatis were inserted in a plasmid between the sigA promoter and the lacZ reporter gene, and expression of the reporter gene was measured. A polypurine sequence, located four bp upstream of the katG translation start codon, increased beta-galactosidase activity and stabilized the lacZ transcript. Mutagenesis of this sequence led to destabilization of the mRNA. Analysis of constructs, in which the polypurine sequence of M. smegmatis was followed by an increasing number of katG codons, demonstrated that mRNA stability requires translation of at least 20 amino acids. In order to define the requirements for the 5' processing of the katG transcript, we created several mutations in this region and analyzed the 5' ends of the transcripts: the distance from the polypurine sequence does not seem to influence the processing, neither the sequence around the cutting point. Only mutations which create a double stranded region around the processing site prevented RNA processing. Conclusion This is the first reported case in mycobacteria, in which both a polypurine sequence and translation initiation are shown to contribute to mRNA stability. The furA-katG mRNA is transcribed from the furA promoter and immediately processed; this processing is prevented by a double stranded RNA at the cutting site, suggesting that the endoribonuclease responsible for the cleavage cuts single stranded RNA.
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Affiliation(s)
- Claudia Sala
- Dipartimento di Scienze Biomolecolari e Biotecnologie, Università degli Studi di Milano, Via Celoria 26, 20133, Milano, Italy.
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Nitric oxide antagonizes the acid tolerance response that protects Salmonella against innate gastric defenses. PLoS One 2008; 3:e1833. [PMID: 18350168 PMCID: PMC2266805 DOI: 10.1371/journal.pone.0001833] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2008] [Accepted: 02/15/2008] [Indexed: 12/28/2022] Open
Abstract
Background Reactive nitrogen species (RNS) derived from dietary and salivary inorganic nitrogen oxides foment innate host defenses associated with the acidity of the stomach. The mechanisms by which these reactive species exert antimicrobial activity in the gastric lumen are, however, poorly understood. Methodology/Principal Findings The genetically tractable acid tolerance response (ATR) that enables enteropathogens to survive harsh acidity was screened for signaling pathways responsive to RNS. The nitric oxide (NO) donor spermine NONOate derepressed the Fur regulon that controls secondary lines of resistance against organic acids. Despite inducing a Fur-mediated adaptive response, acidified RNS largely repressed oral virulence as demonstrated by the fact that Salmonella bacteria exposed to NO donors during mildly acidic conditions were shed in low amounts in feces and exhibited ameliorated oral virulence. NO prevented Salmonella from mounting a de novo ATR, but was unable to suppress an already functional protective response, suggesting that RNS target regulatory cascades but not their effectors. Transcriptional and translational analyses revealed that the PhoPQ signaling cascade is a critical ATR target of NO in rapidly growing Salmonella. Inhibition of PhoPQ signaling appears to contribute to most of the NO-mediated abrogation of the ATR in log phase bacteria, because the augmented acid sensitivity of phoQ-deficient Salmonella was not further enhanced after RNS treatment. Conclusions/Significance Since PhoPQ-regulated acid resistance is widespread in enteric pathogens, the RNS-mediated inhibition of the Salmonella ATR described herein may represent a common component of innate host defenses.
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70
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Reid AN, Pandey R, Palyada K, Whitworth L, Doukhanine E, Stintzi A. Identification of Campylobacter jejuni genes contributing to acid adaptation by transcriptional profiling and genome-wide mutagenesis. Appl Environ Microbiol 2008; 74:1598-612. [PMID: 18192408 PMCID: PMC2258640 DOI: 10.1128/aem.01508-07] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2007] [Accepted: 12/30/2007] [Indexed: 12/17/2022] Open
Abstract
In order to cause disease, the food- and waterborne pathogen Campylobacter jejuni must face the extreme acidity of the host stomach as well as cope with pH fluctuations in the intestine. In the present study, C. jejuni NCTC 11168 was grown under mildly acidic conditions mimicking those encountered in the intestine. The resulting transcriptional profiles revealed how this bacterium fine-tunes gene expression in response to acid stress. This adaptation involves the differential expression of respiratory pathways, the induction of genes for phosphate transport, and the repression of energy generation and intermediary metabolism genes. We also generated and screened a transposon-based mutant library to identify genes required for wild-type levels of growth under mildly acidic conditions. This screen highlighted the important role played by cell surface components (flagella, the outer membrane, capsular polysaccharides, and lipooligosaccharides) in the acid stress response of C. jejuni. Our data also revealed that a limited correlation exists between genes required for growth under acidic conditions and genes differentially expressed in response to acid. To gain a comprehensive picture of the acid stress response of C. jejuni, we merged transcriptional profiles obtained from acid-adapted cells and cells subjected to acid shock. Genes encoding the transcriptional regulator PerR and putative oxidoreductase subunits Cj0414 and Cj0415 were among the few up-regulated under both acid stress conditions. As a Cj0415 mutant was acid sensitive, it is likely that these genes are crucial to the acid stress response of C. jejuni and consequently are important for host colonization.
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Affiliation(s)
- Anne N Reid
- Ottawa Institute of Systems Biology, Department of Biochemistry, Microbiology and Immunology, University of Ottawa, 451 Smyth Road, Ottawa, Ontario K1H 8M5, Canada
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71
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Reid AN, Pandey R, Palyada K, Naikare H, Stintzi A. Identification of Campylobacter jejuni genes involved in the response to acidic pH and stomach transit. Appl Environ Microbiol 2008; 74:1583-97. [PMID: 18192414 PMCID: PMC2258634 DOI: 10.1128/aem.01507-07] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2007] [Accepted: 12/30/2007] [Indexed: 12/11/2022] Open
Abstract
Campylobacter jejuni causes food- and waterborne gastroenteritis, and as such it must survive passage through the stomach in order to reach the gastrointestinal tract. While little is known about how C. jejuni survives transit through the stomach, its low infectious dose suggests it is well equipped to sense and respond to acid shock. In this study, the transcriptional profile of C. jejuni NCTC 11168 was obtained after the organism was exposed to in vitro and in vivo (piglet stomach) acid shock. The observed down-regulation of genes encoding ribosomal proteins likely reflects the need to reshuffle energy toward the expression of components required for survival. Acid shock also caused C. jejuni to up-regulate genes involved in stress responses. These included heat shock genes as well as genes involved in the response to oxidative and nitrosative stress. A role for the chaperone clpB in acid resistance was confirmed in vitro. Some genes showed expression patterns that were markedly different in vivo and in vitro, which likely reflects the complexity of the in vivo environment. For instance, transit through the stomach was characterized by up-regulation of genes that encode products that are involved in the use of nitrite as a terminal electron acceptor and down-regulation of genes that are involved in capsular polysaccharide expression. In conclusion, this study has enabled us to understand how C. jejuni modulates gene expression in response to acid shock in vitro and to correlate this with gene expression profiles of C. jejuni as it transits through the host stomach.
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Affiliation(s)
- Anne N Reid
- Ottawa Institute of Systems Biology, Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada
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72
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Expression of the gonococcal global regulatory protein Fur and genes encompassing the Fur and iron regulon during in vitro and in vivo infection in women. J Bacteriol 2008; 190:3129-39. [PMID: 18310343 DOI: 10.1128/jb.01830-07] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
The ferric uptake regulatory protein, Fur, functions as a global regulatory protein of gene transcription in the mucosal pathogen Neisseria gonorrhoeae. We have shown previously that several N. gonorrhoeae Fur-repressed genes are expressed in vivo during mucosal gonococcal infection in men, which suggests that this organism infects in an iron-limited environment and that Fur is expressed under these conditions. In this study we have demonstrated expression of the gonococcal fur gene in vitro, in human cervical epithelial cells, and in specimens from female subjects with uncomplicated gonococcal infection. In vitro studies confirmed that the expression of the gonococcal fur gene was repressed during growth under iron-replete growth conditions but that a basal level of the protein was maintained. Using GFP transcriptional fusions constructed from specific Fur binding sequences within the fur promoter/operator region, we determined that this operator region was functional during N. gonorrhoeae infection of cervical epithelial cells. Furthermore, reverse transcription-PCR analysis, as well as microarray analysis, using a custom Neisseria Fur and iron regulon microarray revealed that several Fur- and iron-regulated genes were expressed during N. gonorrhoeae infection of cervical epithelial cells. Microarray analysis of specimens obtained from female subjects with uncomplicated gonococcal infection corroborated our in vitro findings and point toward a key role of gonococcal Fur- and iron-regulated genes in gonococcal disease.
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73
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Kitphati W, Ngok-Ngam P, Suwanmaneerat S, Sukchawalit R, Mongkolsuk S. Agrobacterium tumefaciens fur has important physiological roles in iron and manganese homeostasis, the oxidative stress response, and full virulence. Appl Environ Microbiol 2007; 73:4760-8. [PMID: 17545320 PMCID: PMC1951035 DOI: 10.1128/aem.00531-07] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2007] [Accepted: 05/20/2007] [Indexed: 01/14/2023] Open
Abstract
In Agrobacterium tumefaciens, the balance between acquiring enough iron and avoiding iron-induced toxicity is regulated in part by Fur (ferric uptake regulator). A fur mutant was constructed to address the physiological role of the regulator. Atypically, the mutant did not show alterations in the levels of siderophore biosynthesis and the expression of iron transport genes. However, the fur mutant was more sensitive than the wild type to an iron chelator, 2,2'-dipyridyl, and was also more resistant to an iron-activated antibiotic, streptonigrin, suggesting that Fur has a role in regulating iron concentrations. A. tumefaciens sitA, the periplasmic binding protein of a putative ABC-type iron and manganese transport system (sitABCD), was strongly repressed by Mn(2+) and, to a lesser extent, by Fe(2+), and this regulation was Fur dependent. Moreover, the fur mutant was more sensitive to manganese than the wild type. This was consistent with the fact that the fur mutant showed constitutive up-expression of the manganese uptake sit operon. Fur(At) showed a regulatory role under iron-limiting conditions. Furthermore, Fur has a role in determining oxidative resistance levels. The fur mutant was hypersensitive to hydrogen peroxide and had reduced catalase activity. The virulence assay showed that the fur mutant had a reduced ability to cause tumors on tobacco leaves compared to wild-type NTL4.
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Affiliation(s)
- Worawan Kitphati
- Laboratory of Biotechnology, Chulabhorn Research Institute, Lak Si, Bangkok, Thailand
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74
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Prévost K, Salvail H, Desnoyers G, Jacques JF, Phaneuf E, Massé E. The small RNA RyhB activates the translation of shiA mRNA encoding a permease of shikimate, a compound involved in siderophore synthesis. Mol Microbiol 2007; 64:1260-73. [PMID: 17542919 DOI: 10.1111/j.1365-2958.2007.05733.x] [Citation(s) in RCA: 168] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
RyhB is a small RNA (sRNA) that downregulates about 20 genes involved in iron metabolism. It is expressed under low iron conditions and pairs with specific mRNAs to trigger their rapid degradation by the RNA degradosome. In contrast to this, another study has suggested that RyhB also activates several genes by increasing their mRNA level. Among these activated genes is shiA, which encodes a permease of shikimate, an aromatic compound participating in the biosynthesis of siderophores. Here, we demonstrate in vivo and in vitro that RyhB directly pairs at the 5'-untranslated region (5'-UTR) of the shiA mRNA to disrupt an intrinsic inhibitory structure that sequesters the ribosome-binding site (Shine-Dalgarno) and the first translation codon. This is the first demonstration of direct gene activation by RyhB, which has been exclusively described in degradation of mRNAs. Our physiological results indicate that the transported compound of the ShiA permease, shikimate, is important under conditions of RyhB expression, that is, iron starvation. This is demonstrated by growth assays in which shikimate or the siderophore enterochelin correct the growth defect observed for a ryhB mutant in iron-limited media.
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Affiliation(s)
- Karine Prévost
- Département de Biochimie, Groupe ARN, Université de Sherbrooke, Sherbrooke, Québec, Canada
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75
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Abstract
Acid pH often triggers changes in gene expression. However, little is known about the identity of the gene products that sense fluctuations in extracytoplasmic pH. The Gram-negative pathogen Salmonella enterica serovar Typhimurium experiences a number of acidic environments both inside and outside animal hosts. Growth in mild acid (pH 5.8) promotes transcription of genes activated by the response regulator PmrA, but the signalling pathway(s) that mediates this response has thus far remained unexplored. Here we report that this activation requires both PmrA's cognate sensor kinase PmrB, which had been previously shown to respond to Fe3+ and Al3+, and PmrA's post-translational activator PmrD. Substitution of a conserved histidine or of either one of four conserved glutamic acid residues in the periplasmic domain of PmrB severely decreased or abolished the mild acid-promoted transcription of PmrA-activated genes. The PmrA/PmrB system controls lipopolysaccharide modifications mediating resistance to the antibiotic polymyxin B. Wild-type Salmonella grown at pH 5.8 were > 100 000-fold more resistant to polymyxin B than organisms grown at pH 7.7. Our results suggest that protonation of the PmrB periplasmic histidine and/or of the glutamic acid residues activate the PmrA protein, and that mild acid promotes cellular changes resulting in polymyxin B resistance.
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Affiliation(s)
- J Christian Perez
- Program in Molecular Genetics, Howard Hughes Medical Institute, Washington University School of MedicineCampus Box 8230, 660 S. Euclid Ave., St Louis, MO 63110, USA
| | - Eduardo A Groisman
- Department of Molecular Microbiology, Howard Hughes Medical Institute, Washington University School of MedicineCampus Box 8230, 660 S. Euclid Ave., St Louis, MO 63110, USA
- *for correspondence. E-mail ; Tel. (+1) 314 362 3692; Fax (+1) 314 747 8228
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76
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Jung WH, Sham A, White R, Kronstad JW. Iron regulation of the major virulence factors in the AIDS-associated pathogen Cryptococcus neoformans. PLoS Biol 2007; 4:e410. [PMID: 17121456 PMCID: PMC1637126 DOI: 10.1371/journal.pbio.0040410] [Citation(s) in RCA: 176] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2006] [Accepted: 09/22/2006] [Indexed: 11/18/2022] Open
Abstract
Iron overload is known to exacerbate many infectious diseases, and conversely, iron withholding is an important defense strategy for mammalian hosts. Iron is a critical cue for Cryptococcus neoformans because the fungus senses iron to regulate elaboration of the polysaccharide capsule that is the major virulence factor during infection. Excess iron exacerbates experimental cryptococcosis and the prevalence of this disease in Sub-Saharan Africa has been associated with nutritional and genetic aspects of iron loading in the background of the HIV/AIDS epidemic. We demonstrate that the iron-responsive transcription factor Cir1 in Cr. neoformans controls the regulon of genes for iron acquisition such that cir1 mutants are "blind" to changes in external iron levels. Cir1 also controls the known major virulence factors of the pathogen including the capsule, the formation of the anti-oxidant melanin in the cell wall, and the ability to grow at host body temperature. Thus, the fungus is remarkably tuned to perceive iron as part of the disease process, as confirmed by the avirulence of the cir1 mutant; this characteristic of the pathogen may provide opportunities for antifungal treatment.
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Affiliation(s)
- Won Hee Jung
- The Michael Smith Laboratories, Department of Microbiology and Immunology, University of British Columbia, Vancouver, British Columbia, Canada
- Faculty of Land and Food Systems, University of British Columbia, Vancouver, British Columbia, Canada
| | - Anita Sham
- The Michael Smith Laboratories, Department of Microbiology and Immunology, University of British Columbia, Vancouver, British Columbia, Canada
- Faculty of Land and Food Systems, University of British Columbia, Vancouver, British Columbia, Canada
| | - Rick White
- Department of Statistics, University of British Columbia, Vancouver, British Columbia, Canada
| | - James W Kronstad
- The Michael Smith Laboratories, Department of Microbiology and Immunology, University of British Columbia, Vancouver, British Columbia, Canada
- Faculty of Land and Food Systems, University of British Columbia, Vancouver, British Columbia, Canada
- * To whom correspondence should be addressed. E-mail:
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77
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Quatrini R, Lefimil C, Veloso FA, Pedroso I, Holmes DS, Jedlicki E. Bioinformatic prediction and experimental verification of Fur-regulated genes in the extreme acidophile Acidithiobacillus ferrooxidans. Nucleic Acids Res 2007; 35:2153-66. [PMID: 17355989 PMCID: PMC1874648 DOI: 10.1093/nar/gkm068] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2006] [Revised: 01/16/2007] [Accepted: 01/22/2007] [Indexed: 01/12/2023] Open
Abstract
The gamma-proteobacterium Acidithiobacillus ferrooxidans lives in extremely acidic conditions (pH 2) and, unlike most organisms, is confronted with an abundant supply of soluble iron. It is also unusual in that it oxidizes iron as an energy source. Consequently, it faces the challenging dual problems of (i) maintaining intracellular iron homeostasis when confronted with extremely high environmental loads of iron and (ii) of regulating the use of iron both as an energy source and as a metabolic micronutrient. A combined bioinformatic and experimental approach was undertaken to identify Fur regulatory sites in the genome of A. ferrooxidans and to gain insight into the constitution of its Fur regulon. Fur regulatory targets associated with a variety of cellular functions including metal trafficking (e.g. feoPABC, tdr, tonBexbBD, copB, cdf), utilization (e.g. fdx, nif), transcriptional regulation (e.g. phoB, irr, iscR) and redox balance (grx, trx, gst) were identified. Selected predicted Fur regulatory sites were confirmed by FURTA, EMSA and in vitro transcription analyses. This study provides the first model for a Fur-binding site consensus sequence in an acidophilic iron-oxidizing microorganism and lays the foundation for future studies aimed at deepening our understanding of the regulatory networks that control iron uptake, homeostasis and oxidation in extreme acidophiles.
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Affiliation(s)
- Raquel Quatrini
- Center for Bioinformatics and Genome Biology, MIFAB, Life Science Foundation and Andrés Bello University, Santiago, Chile.
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78
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Lee JW, Helmann JD. Functional specialization within the Fur family of metalloregulators. Biometals 2007; 20:485-99. [PMID: 17216355 DOI: 10.1007/s10534-006-9070-7] [Citation(s) in RCA: 318] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2006] [Accepted: 11/28/2006] [Indexed: 01/01/2023]
Abstract
The ferric uptake regulator (Fur) protein, as originally described in Escherichia coli, is an iron-sensing repressor that controls the expression of genes for siderophore biosynthesis and iron transport. Although Fur is commonly thought of as a metal-dependent repressor, Fur also activates the expression of many genes by either indirect or direct mechanisms. In the best studied model systems, Fur functions as a global regulator of iron homeostasis controlling both the induction of iron uptake functions (under iron limitation) and the expression of iron storage proteins and iron-utilizing enzymes (under iron sufficiency). We now appreciate that there is a tremendous diversity in metal selectivity and biological function within the Fur family which includes sensors of iron (Fur), zinc (Zur), manganese (Mur), and nickel (Nur). Despite numerous studies, the mechanism of metal ion sensing by Fur family proteins is still controversial. Other family members use metal catalyzed oxidation reactions to sense peroxide-stress (PerR) or the availability of heme (Irr).
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Affiliation(s)
- Jin-Won Lee
- Department of Microbiology, Cornell University, Wing Hall, Ithaca, NY 14853-8101, USA
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79
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Bai E, Rosell F, Lige B, Mauk M, Lelj-Garolla B, Moore G, Mauk A. Functional characterization of the dimerization domain of the ferric uptake regulator (Fur) of Pseudomonas aeruginosa. Biochem J 2006; 400:385-92. [PMID: 16928194 PMCID: PMC1698609 DOI: 10.1042/bj20061168] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The functional properties of the recombinant C-terminal dimerization domain of the Pseudomonas aeruginosa Fur (ferric uptake regulator) protein expressed in and purified from Escherichia coli have been evaluated. Sedimentation velocity measurements demonstrate that this domain is dimeric, and the UV CD spectrum is consistent with a secondary structure similar to that observed for the corresponding region of the crystallographically characterized wild-type protein. The thermal stability of the domain as determined by CD spectroscopy decreases significantly as pH is increased and increases significantly as metal ions are added. Potentiometric titrations (pH 6.5) establish that the domain possesses a high-affinity and a low-affinity binding site for metal ions. The high-affinity (sensory) binding site demonstrates association constants (K(A)) of 10(+/-7)x10(6), 5.7(+/-3)x10(6), 2.0(+/-2)x10(6) and 2.0(+/-3)x10(4) M(-1) for Ni2+, Zn2+, Co2+ and Mn2+ respectively, while the low-affinity (structural) site exhibits association constants of 1.3(+/-2)x10(6), 3.2(+/-2)x10(4), 1.76(+/-1)x10(5) and 1.5(+/-2)x10(3) M(-1) respectively for the same metal ions (pH 6.5, 300 mM NaCl, 25 degrees C). The stability of metal ion binding to the sensory site follows the Irving-Williams order, while metal ion binding to the partial sensory site present in the domain does not. Fluorescence experiments indicate that the quenching resulting from binding of Co2+ is reversed by subsequent titration with Zn2+. We conclude that the domain is a reasonable model for many properties of the full-length protein and is amenable to some analyses that the limited solubility of the full-length protein prevents.
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Affiliation(s)
- Erdeni Bai
- *Immunological Detection Centre of Huhhot 253 Hospital, Inner Mongolia, 010051, People's Republic of China
| | - Federico I. Rosell
- †Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC, Canada V6T 1Z3
| | - Bao Lige
- †Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC, Canada V6T 1Z3
| | - Marcia R. Mauk
- †Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC, Canada V6T 1Z3
| | - Barbara Lelj-Garolla
- ‡School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich NR4 7TJ, U.K
| | - Geoffrey R. Moore
- ‡School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich NR4 7TJ, U.K
- Correspondence may be addressed to either of these authors (email or )
| | - A. Grant Mauk
- †Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC, Canada V6T 1Z3
- Correspondence may be addressed to either of these authors (email or )
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80
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Belzer C, van Schendel BAM, Kuipers EJ, Kusters JG, van Vliet AHM. Iron-responsive repression of urease expression in Helicobacter hepaticus is mediated by the transcriptional regulator Fur. Infect Immun 2006; 75:745-52. [PMID: 17101656 PMCID: PMC1828516 DOI: 10.1128/iai.01163-06] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Persistent colonization of mucosal surfaces by bacteria in the mammalian host requires concerted expression of colonization factors, depending on the environmental conditions. Helicobacter hepaticus is a urease-positive pathogen that colonizes the intestinal and hepatobiliary tracts of rodents. Here it is reported that urease expression of H. hepaticus is iron repressed by the transcriptional regulator Fur. Iron restriction of growth medium resulted in a doubling of urease activity in wild-type H. hepaticus strain ATCC 51449 and was accompanied by increased levels of urease subunit proteins and ureA mRNA. Insertional inactivation of the fur gene abolished iron-responsive repression of urease activity, whereas inactivation of the perR gene did not affect iron-responsive regulation of urease activity. The iron-responsive promoter element was identified directly upstream of the H. hepaticus ureA gene. Recombinant H. hepaticus Fur protein bound to this ureA promoter region in a metal-dependent matter, and binding resulted in the protection of a 41-bp, Fur box-containing operator sequence located at positions -35 to -75 upstream of the transcription start site. In conclusion, H. hepaticus Fur controls urease expression at the transcriptional level in response to iron availability. This represents a novel type of urease regulation in ureolytic bacteria and extends the already diverse regulatory repertoire of the Fur protein.
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Affiliation(s)
- Clara Belzer
- Department of Gastroenterology and Hepatology, Erasmus MC--University Medical Center, 3015 CE Rotterdam, The Netherlands
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81
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Maciag A, Dainese E, Rodriguez GM, Milano A, Provvedi R, Pasca MR, Smith I, Palù G, Riccardi G, Manganelli R. Global analysis of the Mycobacterium tuberculosis Zur (FurB) regulon. J Bacteriol 2006; 189:730-40. [PMID: 17098899 PMCID: PMC1797298 DOI: 10.1128/jb.01190-06] [Citation(s) in RCA: 200] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The proteins belonging to the Fur family are global regulators of gene expression involved in the response to several environmental stresses and to the maintenance of divalent cation homeostasis. The Mycobacterium tuberculosis genome encodes two Fur-like proteins, FurA and a protein formerly annotated FurB. Since in this paper we show that it represents a zinc uptake regulator, we refer to it as Zur. The gene encoding Zur is found in an operon together with the gene encoding a second transcriptional regulator (Rv2358). In a previous work we demonstrated that Rv2358 is responsible for the zinc-dependent repression of the Rv2358-zur operon, favoring the hypothesis that these genes represent key regulators of zinc homeostasis. In this study we generated a zur mutant in M. tuberculosis, examined its phenotype, and characterized the Zur regulon by DNA microarray analysis. Thirty-two genes, presumably organized in 16 operons, were found to be upregulated in the zur mutant. Twenty-four of them belonged to eight putative transcriptional units preceded by a conserved 26-bp palindrome. Electrophoretic mobility shift experiments demonstrated that Zur binds to this palindrome in a zinc-dependent manner, suggesting its direct regulation of these genes. The proteins encoded by Zur-regulated genes include a group of ribosomal proteins, three putative metal transporters, the proteins belonging to early secretory antigen target 6 (ESAT-6) cluster 3, and three additional proteins belonging to the ESAT-6/culture filtrate protein 10 (CFP-10) family known to contain immunodominant epitopes in the T-cell response to M. tuberculosis infection.
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Affiliation(s)
- Anna Maciag
- Department of Genetics and Microbiology, University of Pavia, Pavia, Italy
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82
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Bearson SMD, Bearson BL, Rasmussen MA. Identification of Salmonella enterica serovar Typhimurium genes important for survival in the swine gastric environment. Appl Environ Microbiol 2006; 72:2829-36. [PMID: 16597989 PMCID: PMC1449006 DOI: 10.1128/aem.72.4.2829-2836.2006] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Since the stomach is a first line of defense for the host against ingested microorganisms, an ex vivo swine stomach contents (SSC) assay was developed to search for genes important for Salmonella enterica serovar Typhimurium survival in the hostile gastric environment. Initial characterization of the SSC assay (pH 3.87) using previously identified, acid-sensitive serovar Typhimurium mutants revealed a 10-fold decrease in survival for a phoP mutant following 20 min of challenge and no survival for mutants of rpoS or fur. To identify additional genes, a signature-tagged mutagenesis bank was constructed and screened in the SSC assay. Nineteen mutants were identified and individually analyzed in the SSC and acid tolerance response assays; 13 mutants exhibited a 10-fold or greater sensitivity in the SSC assay compared to the wild-type strain, but only 3 mutants displayed a 10-fold or greater decrease in survival following pH 3.0 acidic challenge. Further examination determined that the lethal effects of the SSC are pH dependent but that low pH is not the sole killing mechanism(s). Gas chromatography analysis of the SSC revealed lactic acid levels of 126 mM. Upon investigating the effects of lactic acid on serovar Typhimurium survival in a synthetic gastric fluid, not only was a concentration- and time-dependent lethal effect observed, but the phoP, rpoS, fur, and pnp genes were identified as involved in protection against lactic acid exposure. These studies indicate a role in gastric survival for several serovar Typhimurium genes and imply that the stomach environment is defined by more than low pH.
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Affiliation(s)
- Shawn M D Bearson
- US Department of Agriculture, Agricultural Research Service/NADC, 2300 Dayton Ave., Ames, IA 50014, USA.
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83
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Martin-Luna B, Sevilla E, Hernandez JA, Bes MT, Fillat MF, Peleato ML. Fur from Microcystis aeruginosa binds in vitro promoter regions of the microcystin biosynthesis gene cluster. PHYTOCHEMISTRY 2006; 67:876-81. [PMID: 16600317 DOI: 10.1016/j.phytochem.2006.02.005] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/20/2005] [Revised: 01/31/2006] [Accepted: 02/01/2006] [Indexed: 05/08/2023]
Abstract
Promoter regions of the mcy operon from Microcystis aeruginosa PCC7806, which is responsible for microcystin synthesis in this organism, exhibit sequences that are similar to the sequences recognized by Fur (ferric uptake regulator). This DNA-binding protein is a sensor of iron availability and oxidative stress. In the presence of Fe(2+), a dimer of Fur binds the iron-boxes in their target genes, repressing their expression. When iron is absent the expression of those gene products is allowed. Here, we show that Fur from M. aeruginosa binds in vitro promoter regions of several mcy genes, which suggests that Fur might regulate, among other factors, microcystin synthesis. The binding affinity is increased by the presence of metal and DTT, suggesting a response to iron availability and redox status of the cell.
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Affiliation(s)
- Beatriz Martin-Luna
- Departamento de Bioquimica y Biologia Molecular y Celular, Facultad de Ciencias, and BIFI, Universidad de Zaragoza, Spain
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84
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Oglesby AG, Murphy ER, Iyer VR, Payne SM. Fur regulates acid resistance in Shigella flexneri via RyhB and ydeP. Mol Microbiol 2006; 58:1354-67. [PMID: 16313621 DOI: 10.1111/j.1365-2958.2005.04920.x] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Shigella flexneri requires iron for survival, and the genes for iron uptake and homeostasis are regulated by the Fur protein. Microarrays were used to identify genes regulated by Fur and to study the physiological effects of iron availability in S. flexneri. These assays showed that the expression of genes involved in iron acquisition and acid response was induced by low-iron availability and by inactivation of fur. A fur null mutant was acid sensitive in media at pH 2.5, and acid sensitivity was also observed in the wild-type strain grown under iron-limiting conditions. Acid resistance of the fur mutant in minimal medium was restored by addition of glutamate during acid challenge, indicating that the glutamate-dependent acid resistance system was not defective. Inactivation of ryhB, a small regulatory RNA whose expression is repressed by Fur, restored acid resistance in the fur mutant, while overexpressing ryhB increased acid sensitivity in the wild-type strain. RyhB-regulated genes were identified by microarray analysis. The expression of one of the RyhB-repressed genes, ydeP, which encodes a putative oxidoreductase, suppressed acid sensitivity in the fur mutant. Furthermore, an S. flexneri ydeP mutant was defective for both glutamate-independent and glutamate-dependent acid resistance. The repression of ydeP by RyhB may be indirect, as real time polymerase chain reaction (PCR) experiments indicated that RyhB negatively regulates evgA, which encodes an activator of ydeP. These results demonstrate that the acid sensitivity defect of the S. flexneri fur mutant is due to repression of ydeP by RyhB, most likely via repression of evgA.
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Affiliation(s)
- Amanda G Oglesby
- Section of Molecular Genetics and Microbiology, The University of Texas at Austin, Austin, TX 78712, USA
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85
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Kim JS, Sung MH, Kho DH, Lee JK. Induction of manganese-containing superoxide dismutase is required for acid tolerance in Vibrio vulnificus. J Bacteriol 2005; 187:5984-95. [PMID: 16109940 PMCID: PMC1196150 DOI: 10.1128/jb.187.17.5984-5995.2005] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The manganese-containing superoxide dismutase (MnSOD) of Vibrio vulnificus, normally detected after the onset of the stationary phase, is expressed during the lag that immediately follows the transfer of cells grown exponentially to a fresh medium acidified to pH 5.0, whereas Fe-containing SOD is constitutively expressed. The signal triggering the growth lag and MnSOD induction therein is not low pH but intracellular superoxide accumulated under these conditions, since addition of a superoxide scavenger not only shortened the lag but also abrogated the MnSOD induction. If the lysine decarboxylase reaction proceeds in the presence of sufficient lysine, the broth is rapidly neutralized to abolish the generation of oxidative stress. Accordingly, the acid tolerance response was examined without the addition of lysine. SoxR regulates MnSOD induction. Lack of MnSOD caused by mutations in soxR or sodA resulted in low tolerance to low pH. The fur mutant derepressing MnSOD showed better tolerance than the wild type. Thus, an increase in total cytosolic SOD activity through MnSOD induction is essential for the cell to withstand the acid challenge. The contribution of cuprozinc-containing SOD to acid tolerance is not significant compared with those of cytosolic SODs.
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Affiliation(s)
- Ju-Sim Kim
- Department of Life Science and Interdisciplinary Program of Integrated Biotechnology, Sogang University, Seoul 121-742, Korea
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86
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Espinosa V, González AD, Vasconcelos AT, Huerta AM, Collado-Vides J. Comparative studies of transcriptional regulation mechanisms in a group of eight gamma-proteobacterial genomes. J Mol Biol 2005; 354:184-99. [PMID: 16236313 DOI: 10.1016/j.jmb.2005.09.037] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2005] [Revised: 09/12/2005] [Accepted: 09/13/2005] [Indexed: 11/18/2022]
Abstract
Experimental data on the Escherichia coli transcriptional regulation has enabled the construction of statistical models to predict new regulatory elements within its genome. Far less is known about the transcriptional regulatory elements in other gamma-proteobacteria with sequenced genomes, so it is of great interest to conduct comparative genomic studies oriented to extracting biologically relevant information about transcriptional regulation in these less studied organisms using the knowledge from E. coli. In this work, we use the information stored in the TRACTOR_DB database to conduct a comparative study on the mechanisms of transcriptional regulation in eight gamma-proteobacteria and 38 regulons. We assess the conservation of transcription factors binding specificity across all the eight genomes and show a correlation between the conservation of a regulatory site and the structure of the transcription unit it regulates. We also find a marked conservation of site-promoter distances across the eight organisms and a correspondence of the statistical significance of co-occurrence of pairs of transcription factor binding sites in the regulatory regions, which is probably related to a conserved architecture of higher-order regulatory complexes in the organisms studied. The results obtained in this study using the information on transcriptional regulation in E. coli enable us to conclude that not only transcription factor-binding sites are conserved across related species but also several of the transcriptional regulatory mechanisms previously identified in E. coli.
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Affiliation(s)
- Vladimir Espinosa
- National Bioinformatics Center, Industria y San José, Capitolio Nacional, CP. 10200, Habana Vieja, Ciudad de la Habana, Cuba
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87
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Hernández JA, Meier J, Barrera FN, de los Paños OR, Hurtado-Gómez E, Bes MT, Fillat MF, Peleato ML, Cavasotto CN, Neira JL. The conformational stability and thermodynamics of Fur A (ferric uptake regulator) from Anabaena sp. PCC 7119. Biophys J 2005; 89:4188-200. [PMID: 16169981 PMCID: PMC1366984 DOI: 10.1529/biophysj.105.065805] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Fur (ferric uptake regulator) is a key bacterial protein that regulates iron acquisition and its storage, and modulates the expression of genes involved in the response to different environmental stresses. Although the protein is involved in several regulation mechanisms, and members of the Fur family have been identified in pathogen organisms, the stability and thermodynamic characterization of a Fur protein have not been described. In this work, the stability, thermodynamics and structure of the functional dimeric Fur A from Anabaena sp. PCC 7119 were studied by using computational methods and different biophysical techniques, namely, circular dichroism, fluorescence, Fourier-transform infrared, and nuclear magnetic resonance spectroscopies. The structure, as monitored by circular dichroism and Fourier-transform infrared, was composed of a 40% of alpha-helix. Chemical-denaturation experiments indicated that Fur A folded via a two-state mechanism, but its conformational stability was small with a value of DeltaG = 5.3 +/- 0.3 kcal mol(-1) at 298 K. Conversely, Fur A was thermally a highly stable protein. The high melting temperature (Tm = 352 +/- 5 K), despite its moderate conformational stability, can be ascribed to its low heat capacity change upon unfolding, DeltaCp, which had a value of 0.8 +/- 0.1 kcal mol(-1) K(-1). This small value is probably due to burial of polar residues in the Fur A structure. This feature can be used for the design of mutants of Fur A with impaired DNA-binding properties.
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Affiliation(s)
- José A Hernández
- Departamento de Bioquímica y Biología Molecular y Celular, Universidad de Zaragoza, Zaragoza, Spain
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88
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89
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Rychlik I, Barrow PA. Salmonella stress management and its relevance to behaviour during intestinal colonisation and infection. FEMS Microbiol Rev 2005; 29:1021-40. [PMID: 16023758 DOI: 10.1016/j.femsre.2005.03.005] [Citation(s) in RCA: 145] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2004] [Revised: 03/04/2005] [Accepted: 03/30/2005] [Indexed: 01/13/2023] Open
Abstract
The enteric pathogen Salmonella enterica is exposed to a number of stressful environments during its life cycle within and outside its various hosts. During intestinal colonisation Salmonella is successively exposed to acid pH in the stomach, to the detergent-like activity of bile, to decreasing oxygen supply, to the presence of multiple metabolites produced by the normal gut microflora and finally it is exposed to cationic antimicrobial peptides present on the surface of epithelial cells. There are four major regulators controlling relevant stress responses in Salmonella, namely RpoS, PhoPQ, Fur and OmpR/EnvZ. Except for Fur, inactivation of genes encoding the other stress regulators results in attenuated virulence and such mutants can therefore be considered as vaccine candidates. In contrast, a decrease in oxygen supply monitored by Fnr and ArcAB, or oxidative stress controlled by OxyR and SoxRS is not regarded as a stress associated with host colonisation since inactivation of either of these systems does not result in reductions in colonisation. The role of quorum-sensing through luxS and sdiA is also considered as a regulator of virulence and colonisation.
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Affiliation(s)
- Ivan Rychlik
- Veterinary Research Institute, Hudcova 70, 621 32 Brno, Czech Republic.
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90
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Quatrini R, Lefimil C, Holmes DS, Jedlicki E. The ferric iron uptake regulator (Fur) from the extreme acidophile Acidithiobacillus ferrooxidans. Microbiology (Reading) 2005; 151:2005-2015. [PMID: 15942007 DOI: 10.1099/mic.0.27581-0] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Acidithiobacillus ferrooxidansis a Gram-negative bacterium that lives at pH 2 in high concentrations of soluble ferrous and ferric iron, making it an interesting model for understanding the biological mechanisms of bacterial iron uptake and homeostasis in extremely acid conditions. A candidatefurAF(FerricUptakeRegulator) gene was identified in theA. ferrooxidansATCC 23270 genome. FurAFhas significant sequence similarity, including conservation of functional motifs, to known Fur orthologues and exhibits cross-reactivity toEscherichia coliFur antiserum. ThefurAFgene is able to complementfurdeficiency inE. coliin an iron-responsive manner. FurAFis also able to bind specifically toE. coliFur regulatory regions (Fur boxes) and to a candidate Fur box fromA. ferrooxidans, as judged by electrophoretic mobility shift assays. FurAFrepresses gene expression fromE. coliFur-responsive promotersfiuandfhuFwhen expressed at high protein levels. However, it increases gene expression from these promoters at low concentrations and possibly from other Fur-regulated promoters involved in iron-responsive oxidative stress responses.
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Affiliation(s)
- R Quatrini
- Millennium Institute of Fundamental and Applied Biology, Santiago, Chile
- Laboratory of Bioinformatics and Genome Biology, University of Andrés Bello, Santiago, Chile
| | - C Lefimil
- Program of Cellular and Molecular Biology, ICBM, Faculty of Medicine, University of Chile, Santiago, Chile
- Laboratory of Bioinformatics and Genome Biology, University of Andrés Bello, Santiago, Chile
| | - D S Holmes
- Millennium Institute of Fundamental and Applied Biology, Santiago, Chile
- Laboratory of Bioinformatics and Genome Biology, University of Andrés Bello, Santiago, Chile
| | - E Jedlicki
- Program of Cellular and Molecular Biology, ICBM, Faculty of Medicine, University of Chile, Santiago, Chile
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91
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Harvie DR, Vílchez S, Steggles JR, Ellar DJ. Bacillus cereus Fur regulates iron metabolism and is required for full virulence. MICROBIOLOGY-SGM 2005; 151:569-577. [PMID: 15699205 DOI: 10.1099/mic.0.27744-0] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
A homologue of the Bacillus subtilis fur gene was identified in Bacillus cereus and characterized. The predicted amino acid sequence of the cloned gene was found to be highly similar to other members of the Fur family of transcriptional regulators. The B. cereus fur gene was shown to partially complement an Escherichia coli fur mutant. Purified B. cereus Fur bound specifically to a 19 bp DNA sequence homologous to the B. subtilis Fur box in a metal-dependent manner. Analysis of the available B. cereus genome data identified a number of genes which contain predicted Fur box sequences in the promoter region. Many of these genes are predicted to play a role in bacterial iron uptake and metabolism, but several have also been implicated as having a role in virulence. Fur and iron regulation of a siderophore biosynthesis operon was confirmed in a beta-galactosidase assay. A B. cereus fur null strain was constructed by allelic replacement of the chromosomal gene with a copy disrupted with a kanamycin resistance cassette. The Deltafur mutant was found to constitutively express siderophores, to accumulate iron intracellularly to a level approximately threefold greater than the wild-type, and to be hypersensitive to hydrogen peroxide. In an insect infection model, the virulence of the fur null strain was found to be significantly attenuated, highlighting the essential role played by Fur in the virulence of this pathogen.
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Affiliation(s)
- Duncan R Harvie
- Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA, UK
| | - Susana Vílchez
- Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA, UK
| | - James R Steggles
- Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA, UK
| | - David J Ellar
- Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA, UK
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92
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Abstract
The facultative intracellular pathogen Salmonella enterica serovar Typhimurium possesses an elaborate set of virulence genes that enables the bacterium successfully to move between and adapt to the environment, different host organisms and various micro-niches within a given host. Expression of virulence attributes is by no means constitutive. Rather, the regulation of virulence determinants is highly coordinated and integrated into normal bacterial physiological responses. By integrating discriminating virulence gene regulators with conserved housekeeping regulatory processes, the bacteria can sense alterations in the repertoire of environmental cues, and translate the sensing events into a pragmatic and coordinated expression of virulence genes. While the description of transmissible genetic elements that import global gene regulatory factors into a cell brings conceptual problems into the established regulatory network, the existence of mobile gene regulators may actually enable the bacteria to further modulate virulence expression.
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Affiliation(s)
- Mikael Rhen
- Microbiology and Tumor Biology Center, Karolinska Institute, S-171 77 Stockholm, Sweden.
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93
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Antigen Delivery Systems II: Development of Live Recombinant Attenuated Bacterial Antigen and DNA Vaccine Delivery Vector Vaccines. Mucosal Immunol 2005. [DOI: 10.1016/b978-012491543-5/50060-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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94
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van Vliet AHM, Ernst FD, Kusters JG. NikR-mediated regulation of Helicobacter pylori acid adaptation. Trends Microbiol 2004; 12:489-94. [PMID: 15488389 DOI: 10.1016/j.tim.2004.09.005] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Nickel is the cofactor of the Helicobacter pylori urease enzyme, a factor essential for the chronic colonization of the acidic hostile environment in the human stomach. The NikR regulatory protein directly controls urease expression and regulates the uptake of nickel, and is also able to regulate the expression of other regulatory proteins including the iron-responsive regulator Fur. Through regulatory crosstalk and overlapping regulons, the NikR protein controls the expression of many systems important for colonization and acid adaptation. Despite the paucity of regulatory proteins, this enables H. pylori to optimally adapt to conditions in the stomach, making it one of the most successful human pathogens.
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Affiliation(s)
- Arnoud H M van Vliet
- Department of Gastroenterology and Hepatology, Erasmus MC-University Medical Center, Dr. Molewaterplein 40, 3015 GD Rotterdam, The Netherlands.
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95
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Delany I, Rappuoli R, Scarlato V. Fur functions as an activator and as a repressor of putative virulence genes in Neisseria meningitidis. Mol Microbiol 2004; 52:1081-90. [PMID: 15130126 DOI: 10.1111/j.1365-2958.2004.04030.x] [Citation(s) in RCA: 138] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Fur is a well-known iron-responsive repressor of gene transcription, which is used by many bacteria to respond to the low-iron environment that pathogens encounter during infection. Four promoters of Neisseria meningitidis predicted to have Fur-binding boxes were selected to study the molecular interactions between Fur and the promoter regions of genes expected to play a central role in survival and pathogenesis. We demonstrate that Fur acts not only as a repressor, but also as an activator of gene expression both in vivo and in vitro. We report that Fur binds to operators located upstream of three promoters that are positively regulated in vivo by Fur and iron, whereas Fur binds to an operator overlapping the classically iron-repressed tbp promoter. Deletion of the upstream operator in the norB promoter abolished activation of transcription in vivo in response to iron and in vitro in response to Fur. The role of such a dual mechanism of Fur regulation during infection is discussed.
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Affiliation(s)
- Isabel Delany
- Biochemistry and Molecular Biology Unit, IRIS, Chiron S.r.l., Via Fiorentina 1, 53100 Siena, Italy
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96
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Abstract
Most current paradigms of microbial metabolism have been derived from studying cells grown under a variety of nutrient compositions in aqueous environments. With recent advances in genomics and experimental techniques, alternative forms of bacterial growth are increasingly being explored. When propagated on nutrient-rich semi-solid media, several species of bacteria undergo a morphological differentiation into swarmers that are capable of migrating on surfaces. Recent studies indicate that swarmer differentiation represents much more than a motility phenotype, as several clinically important attributes are also co-regulated. We demonstrate that migrating swarmer cells of Salmonella are metabolically differentiated compared to the vegetative swimmer cells grown in the same nutrient environment. Furthermore, once the cells have differentiated, the swarmers remain in this physiological state under conditions that do not promote the initial differentiation. The bacterium's capacity to override some of the classic paradigms of metabolic regulation established in aqueous environments represents a unique physiological response by the pathogen that may be advantageous in polymicrobial environments such as the host.
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Affiliation(s)
- Wook Kim
- Department of Microbiology and Infectious Diseases, University of Calgary, 3330 Hospital Dr. N.W., Calgary, Alberta T2N 4N1, Canada
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97
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Saridakis CE, Johnson RP, Benson A, Ziebell K, Gyles CL. Influence of animal origin and lineage on survival of Escherichia coli O157:H7 strains in strong and weak acid challenges. J Food Prot 2004; 67:1591-6. [PMID: 15330520 DOI: 10.4315/0362-028x-67.8.1591] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Twenty-five strains of Escherichia coli O157:H7 isolated from humans, cattle, and pigs were maintained in HCl (pH 2.5) and in a volatile fatty acid (VFA) mixture (pH 4.0) for up to 6 h at 37 degrees C to assess their ability to survive in acidic conditions that simulate those of the stomach and ileum, respectively. In HCl, the average group survival of bovine strains was significantly higher than that of porcine and human strains, whereas in VFAs, porcine strains were significantly more resistant than bovine and human strains. Bovine strains exhibited significantly higher average survival in HCl than in VFAs. The average survival of strains classified as octamer-based genome scanning (OBGS) lineage II was significantly superior to that of strains classified as OBGS lineage I in HCl. The group of lineage I strains was more resistant in VFAs compared with lineage II, but only after 6 h of challenge. The possible involvement of urease in acid resistance of E. coli O157:H7 was also examined. Although the strains possessed the ureC gene, as shown by PCR, this gene did not appear to contribute to acid resistance under the conditions tested. The data indicate that there is a relationship between acid resistance and source or lineage of O157:H7 strains.
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98
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Hernández JA, López-Gomollón S, Bes M, Fillat MF, Peleato M. Three fur homologues from Anabaena sp. PCC7120: exploring reciprocal protein-promoter recognition. FEMS Microbiol Lett 2004. [DOI: 10.1111/j.1574-6968.2004.tb09658.x] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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99
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Friedman YE, O'Brian MR. The ferric uptake regulator (Fur) protein from Bradyrhizobium japonicum is an iron-responsive transcriptional repressor in vitro. J Biol Chem 2004; 279:32100-5. [PMID: 15148310 DOI: 10.1074/jbc.m404924200] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Fur protein represses transcription of iron-responsive genes in bacteria. The discovery that Fur is a zinc metalloprotein and the use of surrogate metals for Fe(2+) for in vitro studies question whether Fur is a direct iron sensor. In the present study, we show that the affinity of Fur from Bradyrhizobium japonicum (BjFur) for its target DNA increases 30-fold in the presence of metal, with a K(d) value of about 2 nM. DNase I footprinting experiments showed that BjFur protected its binding site within the irr gene promoter in the presence of Fe(2+) but not in the absence of metal, showing that DNA binding is Fe(2+)-dependent. BjFur did not inhibit in vitro transcription from the irr promoter using purified components in the absence of metal, but BjFur repressed transcription in the presence of Fe(2+). Thus, BjFur is an iron-responsive transcriptional repressor in vitro. A regulatory Fe(2+)-binding site (site 1) and a structural Zn(2+)-binding site (site 2) inferred from the recent crystal structure of Fur from Pseudomonas aeruginosa are composed of amino acids highly conserved in many Fur proteins, including BjFur. BjFur mutants containing substitutions in site 1 (BjFurS1) or site 2 (BjFurS2) bound DNA with high affinity and repressed transcription in vitro in an Fe(2+)-dependent manner. Interestingly, only a single dimer of BjFurS2 occupied the irr promoter, whereas the wild type and BjFurS1 displayed one- or two-dimer occupancy. We suggest that the putative functions for metal-binding sites deduced from the structure of P. aeruginosa Fur cannot be extrapolated to bacterial Fur proteins as a whole.
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Affiliation(s)
- Yali E Friedman
- Department of Biochemistry and Witebsky Center for Microbial Pathogenesis and Immunology, State University of New York, Buffalo, 14214, USA
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100
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Vecerek B, Moll I, Afonyushkin T, Kaberdin V, Bläsi U. Interaction of the RNA chaperone Hfq with mRNAs: direct and indirect roles of Hfq in iron metabolism of Escherichia coli. Mol Microbiol 2004; 50:897-909. [PMID: 14617150 DOI: 10.1046/j.1365-2958.2003.03727.x] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The Escherichia coli Sm-like host factor I (Hfq) is thought to play direct and indirect roles in post-transcriptional regulation by targeting small regulatory RNAs and mRNAs. In this study, we have used proteomics to identify new mRNA targets of Hfq. We have identified 11 candidate proteins, synthesis of which was differentially affected in a hfq- background. The effect of Hfq on some of the corresponding mRNAs including fur, gapA, metF, ppiB and sodB mRNA was assessed, using different in vitro and in vivo methods. This allowed us to distinguish between direct and indirect effects of Hfq in modulating the translational activities of these mRNAs. From the collection of mRNAs tested, only fur and sodB mRNA, encoding the master regulator of iron metabolism and the iron superoxide dismutase, respectively, were found to be regulated by Hfq. Fur is known to be a negative regulator of transcription of the small RNA RyhB. Mutations in the sodB leader and compensating mutations in RyhB revealed that RyhB in turn represses translation of sodB mRNA, explaining the previously reported positive control of sodB by Fur. These data assign a role to Hfq in regulation of iron uptake and in switching off of iron scavenger genes.
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Affiliation(s)
- Branislav Vecerek
- Max F. Perutz Laboratories, Department of Microbiology and Genetics, University Department at the Vienna Biocenter, Dr Bohrgasse 9, 1030 Vienna, Austria
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