| 1. |
- Fernández-Vázquez, Jorge, et al.
(author)
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ppGpp, the general stress response alarmone, is required for the expression of the α-Hemolysin toxin in the uropathogenic Escherichia coli isolate, J96
- 2022
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In: International Journal of Molecular Sciences. - : MDPI. - 1661-6596 .- 1422-0067. ; 23:20
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Journal article (peer-reviewed)abstract
- ppGpp is an intracellular sensor that, in response to different types of stress, coordinates the rearrangement of the gene expression pattern of bacteria to promote adaptation and survival to new environmental conditions. First described to modulate metabolic adaptive responses, ppGpp modulates the expression of genes belonging to very diverse functional categories. In Escherichia coli, ppGpp regulates the expression of cellular factors that are important during urinary tract infections. Here, we characterize the role of this alarmone in the regulation of the hlyCABDII operon of the UPEC isolate J96, encoding the toxin α-hemolysin that induces cytotoxicity during infection of bladder epithelial cells. ppGpp is required for the expression of the α-hemolysin encoded in hlyCABDII by stimulating its transcriptional expression. Prototrophy suppressor mutations in a ppGpp-deficient strain restore the α-hemolysin expression from this operon to wild-type levels, confirming the requirement of ppGpp for its expression. ppGpp stimulates hlyCABDII expression independently of RpoS, RfaH, Zur, and H-NS. The expression of hlyCABDII is promoted at 37 °C and at low osmolarity. ppGpp is required for the thermoregulation but not for the osmoregulation of the hlyCABDII operon. Studies in both commensal and UPEC isolates demonstrate that no UPEC specific factor is strictly required for the ppGpp-mediated regulation described. Our data further support the role of ppGpp participating in the coordinated regulation of the expression of bacterial factors required during infection.
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| 2. |
- Balsalobre, Carlos, et al.
(author)
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Cyclic AMP-dependent osmoregulation of crp gene expression in Escherichia coli.
- 2006
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In: J Bacteriol. - 0021-9193. ; 188:16, s. 5935-44
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Journal article (peer-reviewed)abstract
- We have found that the cyclic AMP (cAMP) receptor protein (CRP)-cAMP regulatory complex in Escherichia coli is subject to osmoregulation at the level of crp gene expression. This osmoregulation was lost in a cya mutant strain but could be restored by external addition of cAMP, suggesting that the intracellular level of cAMP is a key factor in the osmoregulation of CRP. The ability of the cell to maintain optimal CRP activity was essential for the growth and survival of the bacteria under low-osmolarity conditions as shown by studies with different crp mutant alleles. A suppressor mutant with a novel amino acid substitution (L124R) in CRP showed restored growth at low osmolarity. CRP(L124R) was not activated by cAMP and was shown to be dominant negative over the wild type. Our findings suggest that the fine-tuning of the CRP activity may be critical for bacterial viability and adaptability to changing osmotic conditions.
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| 3. |
- Balsalobre, Carlos, et al.
(author)
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Release of the type I secreted α-haemolysin via outer membrane vesicles from Escherichia coli
- 2006
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In: Molecular Microbiology. - Hoboken, NJ, United States : Wiley-Blackwell. - 0950-382X .- 1365-2958. ; 59:1, s. 99-112
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Journal article (peer-reviewed)abstract
- The α-haemolysin is an important virulence factor commonly expressed by extraintestinal pathogenic Escherichia coli. The secretion of the α-haemolysin is mediated by the type I secretion system and the toxin reaches the extracellular space without the formation of periplasmic intermediates presumably in a soluble form. Surprisingly, we found that a fraction of this type I secreted protein is located within outer membrane vesicles (OMVs) that are released by the bacteria. The α-haemolysin appeared very tightly associated with the OMVs as judged by dissociation assays and proteinase susceptibility tests. The α-haemolysin in OMVs was cytotoxically active and caused lysis of red blood cells. The OMVs containing the α-haemolysin were distinct from the OMVs not containing α-haemolysin, showing a lower density. Furthermore, they differed in protein composition and one component of the type I secretion system, the TolC protein, was found in the lower density vesicles. Studies of natural isolates of E. coli demonstrated that the localization of α-haemolysin in OMVs is a common feature among haemolytic strains. We propose an alternative pathway for the transport of the type I secreted α-haemolysin from the bacteria to the host cells during bacterial infections.
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| 4. |
- David Cabrer-Panes, Juan, et al.
(author)
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ppGppmediates the growth phase-dependent regulation ofagn43, a phase variable gene, by stimulating its promoter activity
- 2020
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In: Environmental Microbiology Reports. - : John Wiley & Sons. - 1758-2229. ; 12:4, s. 444-453
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Journal article (peer-reviewed)abstract
- Antigen 43 (Ag43) is a self-recognizing outer membrane protein ofEscherichia coliexpressed during intracellular growth and biofilm formation, suggesting a role in infection. The expression ofagn43is under phase variation control, meaning that there are regulatory mechanisms adjusting the percentage ofagn43-expressing cells in the population, in addition to mechanisms modulating the transcriptional expression level in each expressing cell. Phenotypic and transcriptional studies indicate that Ag43 expression is induced upon entry into the stationary phase in a ppGpp-dependent and RpoS-independent manner. The use of single-cell approaches and phase variation deficient strains let to conclude that ppGpp stimulatesagn43promoter activity, rather than affecting the percentage ofagn43-expressing cells. The data highlight the relevance that promoter activity regulation may have, without any involvement of the phase variation state, in the final Ag43 expression output. Theagn43promoter of the MG1655 strain carries an AT-rich discriminator between positions -10 and +1, which is highly conserved among theagn43genes present in the different pathotypes ofE. coli. Remarkably, the AT-rich discriminator is required for the positive transcriptional control mediated by ppGpp.
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| 5. |
- Forns, Núria, et al.
(author)
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Temperature-dependent conjugative transfer of R27 : Role of chromosome- and plasmid-encoded Hha and H-NS proteins
- 2005
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In: Journal of Bacteriology. - Washington : American society of microbiology. - 0021-9193 .- 1098-5530. ; 187:12, s. 3950-3959
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Journal article (peer-reviewed)abstract
- IncHI plasmids encode multiple-antibiotic resistance in Salmonella enterica serovar Typhi. These plasmids have been considered to play a relevant role in the persistence and reemergence of this microorganism. The IncHII plasmid R27, which can be considered the prototype of IncHI plasmids, is thermosensitive for transfer. Conjugation frequency is highest at low temperature (25 to 30 degrees C), decreasing when temperature increases. R27 codifies an H-NS-like protein (open reading frame 164 [ORF164]) and an Hha-like protein (ORF182). The H-NS and Hha proteins participate in the thermoregulation of gene expression in Escherichia coli. Here we investigated the hypothetical role of such proteins in thermoregulation of R27 conjugation. At a nonpermissive temperature (33 degrees C), transcription of several ORFs in both transfer region I (Tra1) and Tra2 from R27 is upregulated in cells depleted of Hha-like and H-NS-like proteins. Both chromosome- and plasmid-encoded Hha and H-NS proteins appear to potentially modulate R27 transfer. The function of R27-encoded Hha-like and H-NS proteins is not restricted to modulation of R27 transfer. Different mutant phenotypes associated with both chromosomal hha and hns mutations are compensated in cells harboring R27.
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| 6. |
- Müller, Claudia M, et al.
(author)
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Type 1 fimbriae, a colonization factor of uropathogenic Escherichia coli, are controlled by the metabolic sensor CRP-cAMP.
- 2009
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In: PLoS pathogens. - : Public Library of Science (PLoS). - 1553-7374. ; 5:2, s. e1000303-
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Journal article (peer-reviewed)abstract
- Type 1 fimbriae are a crucial factor for the virulence of uropathogenic Escherichia coli during the first steps of infection by mediating adhesion to epithelial cells. They are also required for the consequent colonization of the tissues and for invasion of the uroepithelium. Here, we studied the role of the specialized signal transduction system CRP-cAMP in the regulation of type 1 fimbriation. Although initially discovered by regulating carbohydrate metabolism, the CRP-cAMP complex controls a major regulatory network in Gram-negative bacteria, including a broad subset of genes spread into different functional categories of the cell. Our results indicate that CRP-cAMP plays a dual role in type 1 fimbriation, affecting both the phase variation process and fimA promoter activity, with an overall repressive outcome on fimbriation. The dissection of the regulatory pathway let us conclude that CRP-cAMP negatively affects FimB-mediated recombination by an indirect mechanism that requires DNA gyrase activity. Moreover, the underlying studies revealed that CRP-cAMP controls the expression of another global regulator in Gram-negative bacteria, the leucine-responsive protein Lrp. CRP-cAMP-mediated repression is limiting the switch from the non-fimbriated to the fimbriated state. Consistently, a drop in the intracellular concentration of cAMP due to altered physiological conditions (e.g. growth in presence of glucose) increases the percentage of fimbriated cells in the bacterial population. We also provide evidence that the repression of type 1 fimbriae by CRP-cAMP occurs during fast growth conditions (logarithmic phase) and is alleviated during slow growth (stationary phase), which is consistent with an involvement of type 1 fimbriae in the adaptation to stress conditions by promoting biofilm growth or entry into host cells. Our work suggests that the metabolic sensor CRP-cAMP plays a role in coupling the expression of type 1 fimbriae to environmental conditions, thereby also affecting subsequent attachment and colonization of host tissues.
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| 7. |
- Paytubi, Sònia, et al.
(author)
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YdgT, the Hha paralogue in Escherichia coli, forms heteromeric complexes with H-NS and StpA.
- 2004
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In: Mol Microbiol. - 0950-382X. ; 54:1, s. 251-63
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Journal article (peer-reviewed)abstract
- In enteric bacteria, proteins of the Hha/YmoA family play a role in the regulation of gene expression in response to environmental factors. Interaction of both Hha and YmoA with H-NS has been reported, and an Hha/H-NS complex has been shown to modulate expression in Escherichia coli of the haemolysin operon of plasmid pHly152. In addition to the hns gene, the chromosome of E. coli and other enteric bacteria also includes the stpA gene that encodes the StpA protein, an H-NS paralogue. We report here the identification of the Hha paralogue in E. coli, the YdgT protein. As Hha paralogue, YdgT appears to fulfil some of the functions reported for StpA as H-NS paralogue: YdgT is overexpressed in hha mutants and can compensate, at least partially, some of the hha-induced phenotypes. We also demonstrate that YdgT interacts both with H-NS and with StpA. Protein cross-linking studies showed that YdgT/H-NS heteromeric complexes are generated within the bacterial cell. The StpA protein, which is subjected to Lon-mediated turnover, was less stable in the absence of Hha or YdgT. Our findings suggest that Hha, YdgT and StpA may form complexes in vivo.
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| 8. |
- Sjöström, Annika E., 1963-, et al.
(author)
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The SfaXII protein from newborn meningitis E. coli is involved in regulation of motility and type 1 fimbriae expression
- 2009
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In: Microbial Pathogenesis. - : Elsevier Ltd. - 0882-4010 .- 1096-1208. ; 46:5, s. 243-252
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Journal article (peer-reviewed)abstract
- The genomes of pathogenic E. coli may contain several different fimbrial operons. How bacteria regulate and coordinate the choice of fimbrial expression under different circumstances remains largely unanswered. In this report we have investigated the role of the sfaXII gene associated to the SfaII fimbrial determinant in the E. coli isolate IHE3034. sfaXII belongs to a subfamily of genes, the 17kDa genes, located near different fimbrial operons in uropathogenic and newborn meningitis E. coli (NMEC) strains. Using the NMEC isolate IHE3034 and non-pathogenic E. coli strains we found that the sfaXII gene had an inhibitory effect on type 1 fimbriae expression. Down regulation of type 1 fimbriae was exerted at transcriptional level both by inhibiting expression from the fimA promoter and by reducing the frequency of OFF-to-ON switching. The effect of sfaXII on expression of the recombinase FimB that catalyzes OFF to ON switching might explain the described reduction in percentage of ON cells. Moreover, expression of the sfaXII gene strongly influenced motility and flagella production of the NMEC isolate IHE3034. We propose that the sfaXII gene, and presumably other members in the 17kDa gene family, may play a role in the control of virulence related gene expression in pathogenic E. coli.
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| 9. |
- Wirebrand, Lisa, 1986-
(author)
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Global regulatory factors that impact metabolic and lifestyle choices in Pseudomonas putida
- 2017
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Doctoral thesis (other academic/artistic)abstract
- Pseudomonas putida strains have a broad metabolic capacity and are innately resistant to many harmful substances – properties that make them of interest for a number of industrial and biotechnological application. They can rapidly adapt to changes in physico-chemical parameters in the soil and water environments they naturally inhabit. Like other bacteria, they have evolved both specific and cross-acting global regulatory circuits to control endurance traits and life style choices in order to survive. Three such survival tactics are 1) the ability to control flagella-mediated motility to search for metabolically favourable locations, 2) to produce protective biofilm structures to resist environmental insults, and 3) to distinguish the energetically most favourable carbon source amongst an array on offer. These processes are often co-ordinated regulated by intersecting networks that are controlled by global signalling molecules (second messengers) such as the nucleotides ppGpp and c-di-GMP, and globally acting proteins.In the first part of my thesis I present evidence that the PP4397 protein of P. putida is responsible for slowing down flagella-driven motility in response to c-di-GMP signalling from a dual-functional c-di-GMP turnover protein termed PP2258. This connection is expanded upon to present a potential signal transduction pathway from a surface located receptor to PP2258 and the c-di-GMP responsive PP4397 protein, and from there to the flagella motors to determine flagella performance. The transcriptional regulatory studies that accompany this work suggest a means by which transcriptional control may serve to initiate a co-ordinated blocking of de novo flagella biogenesis and slowing-down flagella rotation – two processes needed to enter the biofilm mode of growth. Exiting from a biofilm matrix is also a c-di-GMP elicited behaviour, prompted when nutrients become scarce. In my second piece of work I present evidence that hunger-signals in the form of ppGpp directly control transcription to elevate the levels of a c-di-GMP degrading protein – BifA – which lies at the heart of programed biofilm dispersal. The final part of my thesis, concerns how the global regulatory proteins Hfq and Crc act at multiple levels to subvert catabolism of phenolics to favour other preferred sources of carbon. Evidence is presented that this involves a two-tiered translational repression – one at the level of the master regulator of the system, and another at the level of the catabolic enzymes. This study also revealed a hitherto unsuspected role of Crc in maintenance of an IncP-2 plasmid within a bacterial population. This latter finding has implications for a wide variety of processes encoded by the IncP-2 group of Pseudomonas-specific mega-plasmids.
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| 10. |
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