The Experts below are selected from a list of 108 Experts worldwide ranked by ideXlab platform
Felipe C. Cabello - One of the best experts on this subject based on the ideXlab platform.
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Restricted growth of ent- and tonB mutants of Salmonella enterica serovar Typhi in human Mono Mac 6 monocytic cells
FEMS microbiology letters, 2001Co-Authors: Victoria Y. Gorbacheva, Gustavo Faundez, Henry P. Godfrey, Felipe C. CabelloAbstract:Monocytes and macrophages are an important host defense in humans infected with Salmonella enterica serovar Typhi. Bacterial ability to survive in these cells is therefore a crucial virulence characteristic of this pathogen. In this study, we demonstrate that growth of a Salmonella enterica serovar Typhi Enterochelin synthesis mutant and a tonB mutant in the human monocyte cell line Mono Mac 6 is restricted compared to that of the parental wild-type Ty2 strain. These results suggest that Enterochelin- and TonB-mediated iron uptake plays a role in S. enterica serovar Typhi pathogenesis, and also suggest that mutations in iron uptake may attenuate S. enterica serovar Typhi strains for human beings.
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Salmonella typhi iron uptake mutants are attenuated in mice.
Infection and immunity, 1994Co-Authors: M Furman, A Fica, Manoj Saxena, J L Di Fabio, Felipe C. CabelloAbstract:Iron starvation interferes drastically with the multiplication and virulence of Salmonella typhi mutants defective in Enterochelin synthesis or Enterochelin transport. Growth of these mutants is inhibited in the presence of human sera and unsaturated transferrin and is restored by fully saturated transferrin. The mutants exhibit decreased ability to grow in HeLa cell monolayers and are attenuated in mice. These findings are consistent with the S. typhi Enterochelin system playing a role in the pathogenesis of typhoid fever.
Victoria Y. Gorbacheva - One of the best experts on this subject based on the ideXlab platform.
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Restricted growth of ent- and tonB mutants of Salmonella enterica serovar Typhi in human Mono Mac 6 monocytic cells
FEMS microbiology letters, 2001Co-Authors: Victoria Y. Gorbacheva, Gustavo Faundez, Henry P. Godfrey, Felipe C. CabelloAbstract:Monocytes and macrophages are an important host defense in humans infected with Salmonella enterica serovar Typhi. Bacterial ability to survive in these cells is therefore a crucial virulence characteristic of this pathogen. In this study, we demonstrate that growth of a Salmonella enterica serovar Typhi Enterochelin synthesis mutant and a tonB mutant in the human monocyte cell line Mono Mac 6 is restricted compared to that of the parental wild-type Ty2 strain. These results suggest that Enterochelin- and TonB-mediated iron uptake plays a role in S. enterica serovar Typhi pathogenesis, and also suggest that mutations in iron uptake may attenuate S. enterica serovar Typhi strains for human beings.
Rosalba Lagos - One of the best experts on this subject based on the ideXlab platform.
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the ferric uptake regulator fur and iron availability control the production and maturation of the antibacterial peptide microcin e492
PLOS ONE, 2018Co-Authors: Andres E Marcoleta, Gino Corsini, Octavio Monasterio, Sergio Gutierrezcortez, Felipe Hurtado, Yerko Argandona, Rosalba LagosAbstract:Microcin E492 is a pore-forming bacteriocin with toxic activity against Enterobacteriaceae, which undergoes amyloid aggregation as a mechanism to regulate its toxicity. To be active, it requires the posttranslational attachment to the C-terminus of a glycosylated Enterochelin derivative (salmochelin), a process carried out by the proteins MceC, MceI and MceJ encoded in the MccE492 gene cluster. Both microcin E492 and salmochelin have a proposed role in the virulence of the bacterial pathogen Klebsiella pneumoniae. Besides, Enterochelin is produced as a response to low iron availability and its synthesis is controlled by the global iron regulator Fur. Since the production of active microcin E492 depends on Enterochelin biosynthesis, both processes could be coordinately regulated. In this work, we investigated the role of Fur in the expression of the microcin E492 maturation genes mceCJI. mceC was not regulated by Fur as it occurs with its homolog iroB in Salmonella enterica. We demonstrated that mceJI along with the previously uncharacterized gene mceX are transcribed as a single mRNA, and that Fur binds in vivo to a Fur box located upstream of the mceX-mceJI unit. Also, we established that the expression of these genes decreased in a condition of high iron availability, while this effect is abrogated in a Δfur background. Furthermore, our results indicated that MceX acts as a negative regulator of microcin E492 structural gene expression, coupling its synthesis to the iron-dependent regulatory circuit. Consequently, fur or mceX overexpression led to a significant decrease in the antibacterial activity of cells producing microcin E492. Altogether these results show that both the expression of microcin E492 maturation genes mceJI, and MceX the negative regulator of microcin E492 synthesis, are coordinated with the Enterochelin production by Fur, depending on the iron levels in the medium.
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Model of the iron regulatory circuit controlling microcin E492 production, maturation and antibacterial activity.
2018Co-Authors: Andres E Marcoleta, Gino Corsini, Octavio Monasterio, Felipe Hurtado, Yerko Argandona, Sergio Gutiérrez-cortez, Rosalba LagosAbstract:(A) At low iron availability, no Fur-Fe2+ repressor complexes are available to bind the Fur box located in the promoters of genes participating in the synthesis of Enterochelin (1) and mceX/mceJI genes (2). Thus, high amounts of Enterochelin and salmochelin are produced, and MceJI proteins catalyze the attachment of salmochelin to MccE492 peptide (maturation). Additionally, the MceX regulator partially represses the mceBA genes (3), restricting the production of immature MccE492. In this situation, a high proportion of modified MccE492 is exported, which can enter the target cells through the catechol siderophore receptors, resulting in a high antibacterial activity. The production of a high amount of modified MccE492, likely disfavors its amyloid aggregation, preventing toxin inactivation. (B) At high iron availability, the Fur-Fe2+ complexes repress the ent and mceX/mceJI genes, causing a low production of Enterochelin and salmochelin, a poor MccE492 maturation process, and the release of the negative regulation exerted by MceX over the mceBA genes, allowing a higher expression of the MccE492 precursor. Hence, unmodified MccE492 is predominantly exported, which is not recognized by the siderophore receptors and thus fails to cause a toxic effect. The high proportion of unmodified MccE492 likely favor its aggregation into amyloid fibers, and thus the loss of antibacterial activity. The scheme includes a simplified representation of the actual ent genes organization.
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The Production In Vivo of Microcin E492 with Antibacterial Activity Depends on Salmochelin and EntF
Journal of bacteriology, 2008Co-Authors: Gabriela Mercado, Mario Tello, Octavio Monasterio, Macarena Marín, Rosalba LagosAbstract:Microcin E492 is a channel-forming bacteriocin that is found in two forms, namely, a posttranslationally modified form obtained by the covalent linkage of salmochelin-like molecules to serine 84 and an unmodified form. The production of modified microcin E492 requires the synthesis of Enterochelin, which is subsequently glycosylated by MceC and converted into salmochelin. mceC mutants produced inactive microcin E492, and this phenotype was reversed either by complementation with iroB from Salmonella enterica or by the addition of exogenous salmochelin. Cyclic salmochelin uptake by Escherichia coli occurred mainly through the outer membrane catecholate siderophore receptor Fiu. The production of inactive microcin E492 by mutants in entB and entC was reverted by the addition of the end product of the respective mutated pathway (2,3-dihydroxybenzoic acid and Enterochelin/salmochelin, respectively), while mutants in entF did not produce active microcin E492 in the presence of Enterochelin or salmochelin. The EntF adenylation domain was the only domain required for this microcin E492 maturation step. Inactivation of the enzymatic activity of this domain by site-directed mutagenesis did not prevent the synthesis of active microcin E492 in the presence of salmochelin, indicating that the adenylation activity is not essential for the function of EntF at this stage of microcin E492 maturation.
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The activity of microcin E492 from Klebsiella pneumoniae is regulated by a microcin antagonist
FEMS microbiology letters, 1996Co-Authors: Claudia Orellana, Rosalba LagosAbstract:Microcin E492 is a polypeptide antibiotic that is produced and excreted by Klebsiella pneumoniae. Different growth conditions of the producer strain affect microcin activity. The production of a microcin antagonist is responsible for the changes in microcin activity. The microcin antagonist is induced when cells are iron-deprived, resulting in a low microcin activity. The microcin antagonist was purified using a procedure developed for the isolation of a catechol-type siderophore, and its activity was titrated using purified microcin. The inhibitory effect of the microcin antagonist is not observed when this compound is forming a complex with iron. The same inhibitory effect on microcin activity was obtained using purified Enterochelin from Escherichia coli. The microcin antagonist was identified as Enterochelin through thin-layer chromatography.
Volkmar Braun - One of the best experts on this subject based on the ideXlab platform.
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Iron transport systems of Serratia marcescens.
Journal of bacteriology, 1992Co-Authors: Annemarie Angerer, Barbara Klupp, Volkmar BraunAbstract:Serratia marcescens W225 expresses an unconventional iron(III) transport system. Uptake of Fe3+ occurs in the absence of an iron(III)-solubilizing siderophore, of an outer membrane receptor protein, and of the TonB and ExbBD proteins involved in outer membrane transport. The three SfuABC proteins found to catalyze iron(III) transport exhibit the typical features of periplasmic binding-protein-dependent systems for transport across the cytoplasmic membrane. In support of these conclusions, the periplasmic SfuA protein bound iron chloride and iron citrate but not ferrichrome, as shown by protection experiments against degradation by added V8 protease. The cloned sfuABC genes conferred upon an Escherichia coli aroB mutant unable to synthesize its own Enterochelin siderophore the ability to grow under iron-limiting conditions (in the presence of 0.2 mM 2.2'-dipyridyl). Under extreme iron deficiency (0.4 mM 2.2'-dipyridyl), however, the entry rate of iron across the outer membrane was no longer sufficient for growth. Citrate had to be added in order for iron(III) to be translocated as an iron citrate complex in a FecA- and TonB-dependent manner through the outer membrane and via SfuABC across the cytoplasmic membrane. FecA- and TonB-dependent iron transport across the outer membrane could be clearly correlated with a very low concentration of iron in the medium. Expression of the sfuABC genes in E. coli was controlled by the Fur iron repressor gene. S. marcescens W225 was able to synthesize Enterochelin and take up iron(III) Enterochelin. It contained an iron(III) aerobactin transport system but lacked aerobactin synthesis. This strain was able to utilize the hydroxamate siderophores ferrichrome, coprogen, ferrioxamine B, rhodotorulic acid, and schizokinen as sole iron sources and grew on iron citrate as well. In contrast to E. coli K-12, S. marcescens could utilize heme. DNA fragments of the E. coli fhuA, iut, exbB, and fur genes hybridized with chromosomal S. marcescens DNA fragments, whereas no hybridization was obtained between S. marcescens chromosomal DNA and E. coli fecA, fhuE, and tonB gene fragments. The presence of multiple iron transport systems was also indicated by the increased synthesis of at least five outer membrane proteins (in the molecular weight range of 72,000 to 87,000) after growth in low-iron media. Serratia liquefaciens and Serratia ficaria produced aerobactin, showing that this siderophore also occurs in the genus Serratia.
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4 Iron Transport Systems of Serratia marcescens
1991Co-Authors: Annemarie Angerer, Barbara Klupp, Volkmar BraunAbstract:Serratia marcescens W225 expresses an unconventional iron(III) transport system. Uptake of Fe3+ occurs in the absence of an iron(III)-solubilizing siderophore, of an outer membrane receptor protein, and of the TonB and ExbBD proteins involved in outer membrane transport. The three SfuABC proteins found to catalyze iron(III) transport exhibit the typical features of periplasmic binding-protein-dependent systems for transport across the cytoplasmic membrane. In support of these conclusions, the periplasmic SfuA protein bound iron chloride and iron citrate but not ferrichrome, as shown by protection experiments against degradation by added V8 protease. The cloned sfuABC genes conferred upon an Escherichia coli aroB mutant unable to synthesize its own Enterochelin siderophore the ability to grow under iron-limiting conditions (in the presence of 0.2 mM 2.2'-dipyridyl). Under extreme iron deficiency (0.4 mM 2.2'-dipyridyl), however, the entry rate of iron across the outer membrane was no longer sufficient for growth. Citrate had to be added in order for iron(III) to be translocated as an iron citrate complex in a FecA- and TonB-dependent manner through the outer membrane and via SfuABC across the cytoplasmic membrane. FecA- and TonB-dependent iron transport across the outer membrane could be clearly correlated with a very low concentration of iron in the medium. Expression of the sfuABC genes in E. coli was controlled by the Fur iron repressor gene. S. marcescens W225 was able to synthesize Enterochelin and take up iron(III) Enterochelin. It contained an iron(III
M Furman - One of the best experts on this subject based on the ideXlab platform.
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Salmonella typhi iron uptake mutants are attenuated in mice.
Infection and immunity, 1994Co-Authors: M Furman, A Fica, Manoj Saxena, J L Di Fabio, Felipe C. CabelloAbstract:Iron starvation interferes drastically with the multiplication and virulence of Salmonella typhi mutants defective in Enterochelin synthesis or Enterochelin transport. Growth of these mutants is inhibited in the presence of human sera and unsaturated transferrin and is restored by fully saturated transferrin. The mutants exhibit decreased ability to grow in HeLa cell monolayers and are attenuated in mice. These findings are consistent with the S. typhi Enterochelin system playing a role in the pathogenesis of typhoid fever.