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Avican, Ummehan
Publications (7 of 7) Show all publications
Avican, U., Doruk, T., Östberg, Y., Fahlgren, A. & Forsberg, Å. (2017). The Tat substrate SufI is critical for the ability of Yersinia pseudotuberculosis to cause systemic infection. Infection and Immunity, 85(4), Article ID e00867-16.
Open this publication in new window or tab >>The Tat substrate SufI is critical for the ability of Yersinia pseudotuberculosis to cause systemic infection
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2017 (English)In: Infection and Immunity, ISSN 0019-9567, E-ISSN 1098-5522, Vol. 85, no 4, article id e00867-16Article in journal (Refereed) Published
Abstract [en]

The twin arginine translocation (Tat) system targets folded proteins across the inner membrane and is crucial for virulence in many important humanpathogenic bacteria. Tat has been shown to be required for the virulence of Yersinia pseudotuberculosis, and we recently showed that the system is critical for different virulence-related stress responses as well as for iron uptake. In this study, we wanted to address the role of the Tat substrates in in vivo virulence. Therefore, 22 genes encoding potential Tat substrates were mutated, and each mutant was evaluated in a competitive oral infection of mice. Interestingly, a.sufI mutant was essentially as attenuated for virulence as the Tat-deficient strain. We also verified that SufI was Tat dependent for membrane/periplasmic localization in Y. pseudotuberculosis. In vivo bioluminescent imaging of orally infected mice revealed that both the.sufI and Delta tatC mutants were able to colonize the cecum and Peyer's patches (PPs) and could spread to the mesenteric lymph nodes (MLNs). Importantly, at this point, neither the Delta tatC mutant nor the Delta sufI mutant was able to spread systemically, and they were gradually cleared. Immunostaining of MLNs revealed that both the Delta tatC and Delta sufI mutants were unable to spread from the initial infection foci and appeared to be contained by neutrophils, while wild-type bacteria readily spread to establish multiple foci from day 3 postinfection. Our results show that SufI alone is required for the establishment of systemic infection and is the major cause of the attenuation of the Delta tatC mutant.

Keywords
Yersinia pseudotuberculosis, Tat pathway, virulence, SufI, mesenteric lymph nodes, neutrophils
National Category
Microbiology Immunology
Identifiers
urn:nbn:se:umu:diva-128087 (URN)10.1128/IAI.00867-16 (DOI)000397581800003 ()28115509 (PubMedID)
Available from: 2016-11-22 Created: 2016-11-22 Last updated: 2018-06-09Bibliographically approved
Avican, U., Beckstette, M., Heroven, A. K., Lavander, M., Dersch, P. & Forsberg, Å. (2016). Transcriptomic and Phenotypic Analysis Reveals New Functions for the Tat Pathway in Yersinia pseudotuberculosis. Journal of Bacteriology, 198(20), 2876-2886
Open this publication in new window or tab >>Transcriptomic and Phenotypic Analysis Reveals New Functions for the Tat Pathway in Yersinia pseudotuberculosis
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2016 (English)In: Journal of Bacteriology, ISSN 0021-9193, E-ISSN 1098-5530, Vol. 198, no 20, p. 2876-2886Article in journal (Refereed) Published
Abstract [en]

The twin-arginine translocation (Tat) system mediates the secretion of folded proteins that are identified via an N-terminal signal peptide in bacteria, plants, and archaea. Tat systems are associated with virulence in many bacterial pathogens, and our previous studies revealed that Tat-deficient Yersinia pseudotuberculosis was severely attenuated for virulence. Aiming to identify Tat-dependent pathways and phenotypes of relevance for in vivo infection, we analyzed the global transcriptome of parental and Delta tatC mutant strains of Y. pseudotuberculosis during exponential and stationary growth at 26 degrees C and 37 degrees C. The most significant changes in the transcriptome of the Delta tatC mutant were seen at 26 degrees C during stationary-phase growth, and these included the altered expression of genes related to virulence, stress responses, and metabolism. Subsequent phenotypic analysis based on these transcriptome changes revealed several novel Tat-dependent phenotypes, including decreased YadA expression, impaired growth under iron-limited and high-copper conditions, as well as acidic pH and SDS. Several functionally related Tat substrates were also verified to contribute to these phenotypes. Interestingly, the phenotypic defects observed in the Tat-deficient strain were generally more pronounced than those in mutants lacking the Tat substrate predicted to contribute to that specific function. Altogether, this provides new insight into the impact of Tat deficiency on in vivo fitness and survival/replication of Y. pseudotuberculosis during infection. IMPORTANCE In addition to its established role in mediating the secretion of housekeeping enzymes, the Tat system has been recognized as being involved in infection. In some clinically relevant bacteria, such as Pseudomonas spp., several key virulence determinants can readily be identified among the Tat substrates. In enteropathogens, such as Yersinia spp., there are no obvious virulence determinants among the Tat substrates. Tat mutants show no growth defect in vitro but are highly attenuated in in vivo. This makes Tat an attractive target for the development of novel antimicrobials. Therefore, it is important to establish the causes of the attenuation. Here, we show that the attenuation is likely due to synergistic effects of different Tat-dependent phenotypes that each contributes to lowered in vivo fitness.

National Category
Microbiology in the medical area
Identifiers
urn:nbn:se:umu:diva-127950 (URN)10.1128/JB.00352-16 (DOI)000384347500014 ()27501981 (PubMedID)
Available from: 2016-12-16 Created: 2016-11-21 Last updated: 2018-06-09Bibliographically approved
Avican, U., Beckstette, M., Heroven, A. K., Lavander, M., Dersch, P. & Forsberg, Å. (2016). Transcriptomic and phenotypic analysis reveals new functions for the Tat pathway in Yersinia pseudotuberculosis. Journal of Bacteriology, 198(20), 2876-2886
Open this publication in new window or tab >>Transcriptomic and phenotypic analysis reveals new functions for the Tat pathway in Yersinia pseudotuberculosis
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2016 (English)In: Journal of Bacteriology, ISSN 0021-9193, E-ISSN 1098-5530, Vol. 198, no 20, p. 2876-2886Article in journal (Refereed) Published
Abstract [en]

The Twin-arginine translocation (Tat) system mediates secretion of folded proteins that in bacteria, plants and archaea are identified via an N-terminal signal peptide. Tat systems are associated with virulence in many bacterial pathogens and our previous studies revealed that Tat deficient Yersinia pseudotuberculosis was severely attenuated for virulence. Aiming to identify Tat-dependent pathways and phenotypes of relevance for in vivo infection, we analysed the global transcriptome of parental and ∆tatC mutant strains of Y. pseudotuberculosis during exponential and stationary growth at 26oC and 37oC. The most significant changes in the transcriptome of the ∆tatC mutant were seen at 26oC during stationary phase growth and these included the altered expression of genes related to virulence, stress responses and metabolism. Subsequent phenotypic analysis based on these transcriptome changes revealed several novel Tat-dependent phenotypes including decreased YadA expression, impaired growth under iron-limiting and high copper conditions as well as acidic pH and SDS. Several functionally related Tat substrates were also verified to contribute to these phenotypes. Interestingly, the phenotypic defects observed in the Tat-deficient strain were generally more pronounced than in mutants lacking the Tat substrate predicted to contribute to that specific function. Altogether, this provides new insight into the impact of Tat deficiency on in vivo fitness and survival/replication of Y. pseudotuberculosis during infection.

Place, publisher, year, edition, pages
Washington: American Society for Microbiology, 2016
Keywords
Yersinia pseudotuberculosis, Tat pathway, virulence, stress response, transcriptome analysis
National Category
Microbiology Bioinformatics and Systems Biology Biochemistry and Molecular Biology
Research subject
Infectious Diseases; Microbiology; Molecular Biology
Identifiers
urn:nbn:se:umu:diva-128029 (URN)10.1128/JB.00352-16 (DOI)000384347500014 ()
Available from: 2016-11-22 Created: 2016-11-22 Last updated: 2018-06-09Bibliographically approved
Avican, U. (2016). Twin-arginine translocation in Yersinia: the substrates and their role in virulence. (Doctoral dissertation). Umeå: Umeå University
Open this publication in new window or tab >>Twin-arginine translocation in Yersinia: the substrates and their role in virulence
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Pathogenic Yersinia cause a manifold of diseases in humans ranging from mild gastroenteritis (Y. pseudotuberculosis and Y. enterocolitica) to pneumonic and bubonic plague (Y. pestis), while all three have a common virulence strategy that relies on a well-studied type III secretion system and its effector proteins to colonize the host and evade immune responses. However, the role of other protein secretion and/or translocation systems in virulence of Yersinia species is not well known. In this thesis, we sought to investigate the contribution of twin-arginine translocation (Tat) pathway and its secreted substrates to the physiology and virulence of Y. pseudotuberculosis. Tat pathway uniquely exports folded proteins including virulence factors across the cytoplasmic membranes of bacteria. The proteins exported by Tat pathway contain a highly conserved twin-arginine motif in the N-terminal signal peptide. We found that the loss of Tat pathway causes a drastic change of the transcriptome of Y. pseudotuberculosis in stationary phase at environmental temperature with differential regulation of genes involved in virulence, carbon metabolism and stress responses. Phenotypic analysis revealed novel phenotypes of the Tat-deficient strain with defects in iron acquisition, acid resistance, copper oxidation and envelope integrity, which we were partly able to associate with the related Tat substrates. Moreover, increased glucose consumption and accumulation of intracellular fumarate were observed in response to inactivation of Tat pathway implicating a generic effect in cellular physiology. We evaluated the direct role of 22 in silico predicted Tat substrate mutants in the mouse infection model and found only one strain, ΔsufI, exhibited a similar degree of attenuation as Tat-deficient strain. Comparative in vivo characterization studies demonstrated a minor defect for ΔsufI in colonization of intestinal tissues compared to the Tat-deficient strain during early infection, whereas both SufI and TatC were required for dissemination from mesenteric lymph nodes and further systemic spread during late infection. This verifies that SufI has a major role in attenuation seen for the Tat deficient strain both during late infection and initial colonization. It is possible that other Tat substrates such as those involved in iron acquisition and copper resistance also has a role in establishing infection. Further phenotypic analysis indicated that SufI function is required for cell division and stress-survival. Transcriptomic analysis revealed that the highest number of differentially regulated genes in response to loss of Tat and SufI were involved in metabolism and transport. Taken together, this thesis presents a thorough analysis of the involvement of Tat pathway in the overall physiology and virulence strategies of Y. pseudotuberculosis. Finally, we propose that strong effects in virulence render TatC and SufI as potential targets for development of novel antimicrobial compounds

Place, publisher, year, edition, pages
Umeå: Umeå University, 2016. p. 73
Keywords
Yersinia pseudotuberculosis, Tat, virulence, Tat substrates, SufI, stress response, metabolism, infection, transcriptome analysis
National Category
Biochemistry and Molecular Biology Bioinformatics and Systems Biology Microbiology
Research subject
Infectious Diseases; Molecular Biology; Microbiology
Identifiers
urn:nbn:se:umu:diva-128090 (URN)978-91-7601-607-7 (ISBN)
Public defence
2016-12-16, Major Groove, Biomedicinhuset, Byggnad 6L, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2016-11-25 Created: 2016-11-22 Last updated: 2018-06-09Bibliographically approved
Amer, A., Costa, T., Farag, S., Avican, U., Forsberg, Å. & Francis, M. (2013). Genetically engineered frameshifted YopN-TyeA chimeras influence type III secretion system function in Yersinia pseudotuberculosis. PLoS ONE, 8(10), Article ID e77767.
Open this publication in new window or tab >>Genetically engineered frameshifted YopN-TyeA chimeras influence type III secretion system function in Yersinia pseudotuberculosis
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2013 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 8, no 10, article id e77767Article in journal (Refereed) Published
Abstract [en]

Type III secretion is a tightly controlled virulence mechanism utilized by many gram negative bacteria to colonize their eukaryotic hosts. To infect their host, human pathogenic Yersinia spp. translocate protein toxins into the host cell cytosol through a preassembled Ysc-Yop type III secretion device. Several of the Ysc-Yop components are known for their roles in controlling substrate secretion and translocation. Particularly important in this role is the YopN and TyeA heterodimer. In this study, we confirm that Y. pseudotuberculosis naturally produce a 42 kDa YopN-TyeA hybrid protein as a result of a +1 frame shift near the 3 prime of yopN mRNA, as has been previously reported for the closely related Y. pestis. To assess the biological role of this YopN-TyeA hybrid in T3SS by Y. pseudotuberculosis, we used in cis site-directed mutagenesis to engineer bacteria to either produce predominately the YopN-TyeA hybrid by introducing +1 frame shifts to yopN after codon 278 or 287, or to produce only singular YopN and TyeA polypeptides by introducing yopN sequence from Y. enterocolitica, which is known not to produce the hybrid. Significantly, the engineered 42 kDa YopN-TyeA fusions were abundantly produced, stable, and were efficiently secreted by bacteria in vitro. Moreover, these bacteria could all maintain functionally competent needle structures and controlled Yops secretion in vitro. In the presence of host cells however, bacteria producing the most genetically altered hybrids (+1 frameshift after 278 codon) had diminished control of polarized Yop translocation. This corresponded to significant attenuation in competitive survival assays in orally infected mice, although not at all to the same extent as Yersinia lacking both YopN and TyeA proteins. Based on these studies with engineered polypeptides, most likely a naturally occurring YopN-TyeA hybrid protein has the potential to influence T3S control and activity when produced during Yersinia-host cell contact.

Place, publisher, year, edition, pages
San Francisco: Public Library of Science, 2013
Keywords
secretion control, hierarchy, translocation, InvE family, ribosome slippage, virulence
National Category
Microbiology Biochemistry and Molecular Biology Microbiology in the medical area
Research subject
Microbiology
Identifiers
urn:nbn:se:umu:diva-81379 (URN)10.1371/journal.pone.0077767 (DOI)000325483600088 ()24098594 (PubMedID)
Funder
Swedish Research Council
Available from: 2013-10-08 Created: 2013-10-08 Last updated: 2019-11-12Bibliographically approved
Amer, A., Costa, T., Gurung,, J., Avican, U., Forsberg, Å. & Francis, M.Functional consequences of site-directed mutagenesis in theC-terminus of YopN, a Yersinia pseudotuberculosis regulator ofYop secretion.
Open this publication in new window or tab >>Functional consequences of site-directed mutagenesis in theC-terminus of YopN, a Yersinia pseudotuberculosis regulator ofYop secretion
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Pathogenic Yersinia spp. utilizes the Ysc-Yop type III secretion system to targetYop effector proteins into the cytosol of host immune cells. Internalizedeffectors alter specific signaling pathways to neutralize immune cell-dependentphagocytosis, killing and pro-inflammatory responsiveness. This enablesextracellular bacterial multiplication and survival in immune tissue. Central tothe temporal control of Yop type III secretion is the regulator YopN. Incomplex with TyeA, YopN acts to plug the inner face of the type III secretionchannel, denying entry to other Yop substrates until after YopN has beensecreted. A +1 frameshift event in the 3-prime end of yopN results in thesynthesis of a singular secreted YopN-TyeA polypeptide chimera that retainssome regulatory function. As the C-terminal coding sequence of YopN in thishybrid product differs greatly from native sequence, we used site-directedmutagenesis to determine the functional significance of this segment. YopNtruncated at residue 287 or containing a shuffled sequence covering 288 to 293retains full function both in vitro and in vivo. Thus, the extreme C-terminus isapparently superfluous to YopN function. In contrast, a YopN varianttruncated after residue 278 was completely unstable, and these bacteria hadlost all control of T3S activity, and failed to defend against immune cell killing.Interestingly, inclusion of a shuffled sequence from residues 279 to 287recovered some T3S control over function. Hence, the YopN segmentencompassing 279 to 287 is essential for full function, although the exact aminoacid sequence is less important.

National Category
Microbiology in the medical area
Research subject
Microbiology
Identifiers
urn:nbn:se:umu:diva-70112 (URN)
Projects
Controlling substrate export by the Ysc-Yop type III secretion system in Yersinia
Available from: 2013-05-05 Created: 2013-05-05 Last updated: 2018-06-08Bibliographically approved
Avican, U., Avican, K., Fällman, M. & Forsberg, Å.Transcriptomic and phenotypic analysis of sufI and tatC mutants of Yersinia pseudotuberculosis.
Open this publication in new window or tab >>Transcriptomic and phenotypic analysis of sufI and tatC mutants of Yersinia pseudotuberculosis
(English)Manuscript (preprint) (Other academic)
National Category
Microbiology Biochemistry and Molecular Biology Bioinformatics and Systems Biology
Identifiers
urn:nbn:se:umu:diva-128089 (URN)
Available from: 2016-11-22 Created: 2016-11-22 Last updated: 2018-06-09
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