Umeå University's logo

umu.sePublications
Change search
Link to record
Permanent link

Direct link
Sixt, Barbara SusanneORCID iD iconorcid.org/0000-0002-5607-8902
Publications (10 of 19) Show all publications
Bastidas, R. J., Kędzior, M., Davidson, R. K., Walsh, S. C., Dolat, L., Sixt, B. S., . . . Valdivia, R. H. (2024). The acetylase activity of Cdu1 regulates bacterial exit from infected cells by protecting Chlamydia effectors from degradation. eLIFE, 12, Article ID 87386.
Open this publication in new window or tab >>The acetylase activity of Cdu1 regulates bacterial exit from infected cells by protecting Chlamydia effectors from degradation
Show others...
2024 (English)In: eLIFE, E-ISSN 2050-084X, Vol. 12, article id 87386Article in journal (Refereed) Epub ahead of print
Abstract [en]

Many cellular processes are regulated by ubiquitin-mediated proteasomal degradation. Pathogens can regulate eukaryotic proteolysis through the delivery of proteins with de-ubiquitinating (DUB) activities. The obligate intracellular pathogen Chlamydia trachomatis secretes Cdu1 (ChlaDUB1), a dual deubiquitinase and Lys-acetyltransferase, that promotes Golgi remodeling and survival of infected host cells presumably by regulating the ubiquitination of host and bacterial proteins. Here, we determined that Cdu1's acetylase but not its DUB activity is important to protect Cdu1 from ubiquitin-mediated degradation. We further identified three C. trachomatis proteins on the pathogen-containing vacuole (InaC, IpaM, and CTL0480) that required Cdu1's acetylase activity for protection from degradation and determined that Cdu1 and these Cdu1-protected proteins are required for optimal egress of Chlamydia from host cells. These findings highlight a non-canonical mechanism of pathogen-mediated protection of virulence factors from degradation after their delivery into host cells and the coordinated regulation of secreted effector proteins.

Place, publisher, year, edition, pages
eLife Sciences Publications Ltd, 2024
Keywords
acetylase, bacterial effectors, bacterial host exit, Chlamydia trachomatis, deubiquitinase, infectious disease, microbiology, ubiquitin
National Category
Microbiology in the medical area
Identifiers
urn:nbn:se:umu:diva-221552 (URN)10.7554/eLife.87386 (DOI)38358795 (PubMedID)2-s2.0-85185349117 (Scopus ID)
Available from: 2024-03-06 Created: 2024-03-06 Last updated: 2024-03-06
Meier, K., Jachmann, L. H., Türköz, G., Babu Sait, M. R., Pérez, L., Kepp, O., . . . Sixt, B. S. (2023). The Chlamydia effector CpoS modulates the inclusion microenvironment and restricts the interferon response by acting on Rab35. mBio, 14(4), Article ID e0319022.
Open this publication in new window or tab >>The Chlamydia effector CpoS modulates the inclusion microenvironment and restricts the interferon response by acting on Rab35
Show others...
2023 (English)In: mBio, ISSN 2161-2129, E-ISSN 2150-7511, Vol. 14, no 4, article id e0319022Article in journal (Refereed) Published
Abstract [en]

The obligate intracellular bacterium Chlamydia trachomatis inserts a family of inclusion membrane (Inc) proteins into the membrane of its vacuole (the inclusion). The Inc CpoS is a critical suppressor of host cellular immune surveillance, but the underlying mechanism remained elusive. By complementing a cpoS mutant with various natural orthologs and variants of CpoS, we linked distinct molecular interactions of CpoS to distinct functions. Unexpectedly, we found CpoS to be essential for the formation of inclusion membrane microdomains that control the spatial organization of multiple Incs involved in signaling and modulation of the host cellular cytoskeleton. While the function of CpoS in microdomains was uncoupled from its role in the suppression of host cellular defenses, we found the ability of CpoS to interact with Rab GTPases to be required not only for the manipulation of membrane trafficking, such as to mediate transport of ceramide-derived lipids (sphingolipids) to the inclusion, but also for the inhibition of Stimulator of interferon genes (STING)-dependent type I interferon responses. Indeed, depletion of Rab35 phenocopied the exacerbated interferon responses observed during infection with CpoS-deficient mutants. Overall, our findings highlight the role of Inc-Inc interactions in shaping the inclusion microenvironment and the modulation of membrane trafficking as a pathogenic immune evasion strategy.

IMPORTANCE: Chlamydia trachomatis is a prevalent bacterial pathogen that causes blinding ocular scarring and urogenital infections that can lead to infertility and pregnancy complications. Because Chlamydia can only grow within its host cell, boosting the intrinsic defenses of human cells may represent a novel strategy to fight pathogen replication and survival. Hence, CpoS, a Chlamydia protein known to block host cellular defenses, or processes regulated by CpoS, could provide new opportunities for therapeutic intervention. By revealing CpoS as a multifunctional virulence factor and by linking its ability to block host cellular immune signaling to the modulation of membrane trafficking, the present work may provide a foundation for such rationale targeting and advances our understanding of how intracellular bacteria can shape and protect their growth niche.

Place, publisher, year, edition, pages
American Society for Microbiology, 2023
Keywords
cell-autonomous immunity, interferon responses, intracellular bacteria, membrane microdomains, membrane trafficking, Rab GTPases
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:umu:diva-214251 (URN)10.1128/mbio.03190-22 (DOI)001041120000001 ()37530528 (PubMedID)2-s2.0-85169501656 (Scopus ID)
Funder
European Commission, PIOF-GA-2013-626116Swedish Research Council, 2016-06598Swedish Research Council, 2018-02286Swedish Research Council, 2021-06602Swedish Research Council, 2022-00852NIH (National Institutes of Health), AI100759; AI134891
Available from: 2023-09-18 Created: 2023-09-18 Last updated: 2023-09-18Bibliographically approved
Ölander, M. & Sixt, B. S. (2022). Bringing genetics to heretofore intractable obligate intracellular bacterial pathogens: Chlamydia and beyond. PLoS Pathogens, 18(7), Article ID e1010669.
Open this publication in new window or tab >>Bringing genetics to heretofore intractable obligate intracellular bacterial pathogens: Chlamydia and beyond
2022 (English)In: PLoS Pathogens, ISSN 1553-7366, E-ISSN 1553-7374, Vol. 18, no 7, article id e1010669Article in journal (Refereed) Published
Place, publisher, year, edition, pages
Public Library of Science, 2022
National Category
Microbiology in the medical area Infectious Medicine Genetics
Identifiers
urn:nbn:se:umu:diva-198494 (URN)10.1371/journal.ppat.1010669 (DOI)000937106800001 ()35901011 (PubMedID)2-s2.0-85135203391 (Scopus ID)
Funder
Swedish Research Council, 2018-02286Swedish Research Council, 2021-06602
Available from: 2022-08-12 Created: 2022-08-12 Last updated: 2023-09-05Bibliographically approved
Halter, T., Köstlbacher, S., Collingro, A., Sixt, B. S., Tönshoff, E. R., Hendrickx, F., . . . Horn, M. (2022). Ecology and evolution of chlamydial symbionts of arthropods. ISME Communications, 2(1), Article ID 45.
Open this publication in new window or tab >>Ecology and evolution of chlamydial symbionts of arthropods
Show others...
2022 (English)In: ISME Communications, E-ISSN 2730-6151, Vol. 2, no 1, article id 45Article in journal (Refereed) Published
Abstract [en]

The phylum Chlamydiae consists of obligate intracellular bacteria including major human pathogens and diverse environmental representatives. Here we investigated the Rhabdochlamydiaceae, which is predicted to be the largest and most diverse chlamydial family, with the few described members known to infect arthropod hosts. Using published 16 S rRNA gene sequence data we identified at least 388 genus-level lineages containing about 14 051 putative species within this family. We show that rhabdochlamydiae are mainly found in freshwater and soil environments, suggesting the existence of diverse, yet unknown hosts. Next, we used a comprehensive genome dataset including metagenome assembled genomes classified as members of the family Rhabdochlamydiaceae, and we added novel complete genome sequences of Rhabdochlamydia porcellionis infecting the woodlouse Porcellio scaber, and of 'Candidatus R. oedothoracis' associated with the linyphiid dwarf spider Oedothorax gibbosus. Comparative analysis of basic genome features and gene content with reference genomes of well-studied chlamydial families with known host ranges, namely Parachlamydiaceae (protist hosts) and Chlamydiaceae (human and other vertebrate hosts) suggested distinct niches for members of the Rhabdochlamydiaceae. We propose that members of the family represent intermediate stages of adaptation of chlamydiae from protists to vertebrate hosts. Within the genus Rhabdochlamydia, pronounced genome size reduction could be observed (1.49-1.93 Mb). The abundance and genomic distribution of transposases suggests transposable element expansion and subsequent gene inactivation as a mechanism of genome streamlining during adaptation to new hosts. This type of genome reduction has never been described before for any member of the phylum Chlamydiae. This study provides new insights into the molecular ecology, genomic diversity, and evolution of representatives of one of the most divergent chlamydial families.

Place, publisher, year, edition, pages
Springer Nature, 2022
National Category
Microbiology Evolutionary Biology
Identifiers
urn:nbn:se:umu:diva-218940 (URN)10.1038/s43705-022-00124-5 (DOI)001105609100001 ()37938728 (PubMedID)
Available from: 2024-01-03 Created: 2024-01-03 Last updated: 2024-01-03Bibliographically approved
Sixt, B. S. (2022). Keeping the home intact—lessons from Chlamydia. Cell Host and Microbe, 30(4), 475-479
Open this publication in new window or tab >>Keeping the home intact—lessons from Chlamydia
2022 (English)In: Cell Host and Microbe, ISSN 1931-3128, E-ISSN 1934-6069, Vol. 30, no 4, p. 475-479Article in journal, Editorial material (Other academic) Published
Abstract [en]

5 years ago, my colleagues and I revealed the Chlamydia trachomatis virulence factor CpoS as a suppressor of host cell-autonomous immunity. Here, I reflect on the events that inspired and enabled this research and place our discoveries in context to past and most recent discoveries in the field.

Place, publisher, year, edition, pages
Cell Press, 2022
National Category
Cell and Molecular Biology Infectious Medicine
Identifiers
urn:nbn:se:umu:diva-194267 (URN)10.1016/j.chom.2022.03.012 (DOI)35421347 (PubMedID)2-s2.0-85127760068 (Scopus ID)
Available from: 2022-04-29 Created: 2022-04-29 Last updated: 2022-04-29Bibliographically approved
Sixt, B. S. (2021). Host cell death during infection with Chlamydia: a double-edged sword. FEMS Microbiology Reviews, 45(1), Article ID fuaa043.
Open this publication in new window or tab >>Host cell death during infection with Chlamydia: a double-edged sword
2021 (English)In: FEMS Microbiology Reviews, ISSN 0168-6445, E-ISSN 1574-6976, Vol. 45, no 1, article id fuaa043Article in journal (Refereed) Published
Abstract [en]

The phylum Chlamydiae constitutes a group of obligate intracellular bacteria that infect a remarkably diverse range of host species. Some representatives are significant pathogens of clinical or veterinary importance. For instance, Chlamydia trachomatis is the leading infectious cause of blindness and the most common bacterial agent of sexually transmitted diseases. Chlamydiae are exceptionally dependent on their eukaryotic host cells as a consequence of their developmental biology. At the same time, host cell death is an integral part of the chlamydial infection cycle. It is therefore not surprising that the bacteria have evolved exquisite and versatile strategies to modulate host cell survival and death programs to their advantage. The recent introduction of tools for genetic modification of Chlamydia spp., in combination with our increasing awareness of the complexity of regulated cell death in eukaryotic cells, and in particular of its connections to cell-intrinsic immunity, has revived the interest in this virulence trait. However, recent advances also challenged long-standing assumptions and highlighted major knowledge gaps. This review summarizes current knowledge in the field and discusses possible directions for future research, which could lead us to a deeper understanding of Chlamydia's virulence strategies and may even inspire novel therapeutic approaches.

Place, publisher, year, edition, pages
Oxford University Press, 2021
Keywords
bacterial exit, bacterial toxicity, cell-autonomous immunity, intracellular bacteria, regulated cell death, virulence strategies
National Category
Microbiology in the medical area Cell and Molecular Biology
Identifiers
urn:nbn:se:umu:diva-181820 (URN)10.1093/femsre/fuaa043 (DOI)000648700700005 ()32897321 (PubMedID)2-s2.0-85099721200 (Scopus ID)
Available from: 2021-03-26 Created: 2021-03-26 Last updated: 2023-09-05Bibliographically approved
Fluckiger, A., Daillere, R., Sassi, M., Sixt, B. S., Liu, P., Loos, F., . . . Zitvogel, L. (2020). Cross-reactivity between tumor MHC class I-restricted antigens and an enterococcal bacteriophage. Science, 369(6506), 936-942
Open this publication in new window or tab >>Cross-reactivity between tumor MHC class I-restricted antigens and an enterococcal bacteriophage
Show others...
2020 (English)In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 369, no 6506, p. 936-942Article in journal (Refereed) Published
Abstract [en]

Intestinal microbiota have been proposed to induce commensal-specific memory T cells that cross-react with tumor-associated antigens. We identified major histocompatibility complex (MHC) class I-binding epitopes in the tail length tape measure protein (TMP) of a prophage found in the genome of the bacteriophage Enterococcus hirae. Mice bearing E. hirae harboring this prophage mounted a TMP-specific H-2K(b)-restricted CD8(+) T lymphocyte response upon immunotherapy with cyclophosphamide or anti-PD-1 antibodies. Administration of bacterial strains engineered to express the TMP epitope improved immunotherapy in mice. In renal and lung cancer patients, the presence of the enterococcal prophage in stools and expression of a TMP-cross-reactive antigen by tumors correlated with long-term benefit of PD-1 blockade therapy. In melanoma patients, T cell clones recognizing naturally processed cancer antigens that are cross-reactive with microbial peptides were detected.

Place, publisher, year, edition, pages
American Association for the Advancement of Science (AAAS), 2020
National Category
Cancer and Oncology Immunology in the medical area
Identifiers
urn:nbn:se:umu:diva-175131 (URN)10.1126/science.aax0701 (DOI)000562436800041 ()32820119 (PubMedID)2-s2.0-85089769475 (Scopus ID)
Available from: 2020-09-24 Created: 2020-09-24 Last updated: 2024-03-19Bibliographically approved
Schott, B. H., Antonia, A. L., Wang, L., Pittman, K. J., Sixt, B. S., Barnes, A. B., . . . Ko, D. C. (2020). Modeling of variables in cellular infection reveals CXCL10 levels are regulated by human genetic variation and the Chlamydia-encoded CPAF protease. Scientific Reports, 10(1), Article ID 18269.
Open this publication in new window or tab >>Modeling of variables in cellular infection reveals CXCL10 levels are regulated by human genetic variation and the Chlamydia-encoded CPAF protease
Show others...
2020 (English)In: Scientific Reports, E-ISSN 2045-2322, Vol. 10, no 1, article id 18269Article in journal (Refereed) Published
Abstract [en]

Susceptibility to infectious diseases is determined by a complex interaction between host and pathogen. For infections with the obligate intracellular bacterium Chlamydia trachomatis, variation in immune activation and disease presentation are regulated by both host genetic diversity and pathogen immune evasion. Previously, we discovered a single nucleotide polymorphism (rs2869462) associated with absolute abundance of CXCL10, a pro-inflammatory T-cell chemokine. Here, we report that levels of CXCL10 change during C. trachomatis infection of cultured cells in a manner dependent on both host and pathogen. Linear modeling of cellular traits associated with CXCL10 levels identified a strong, negative correlation with bacterial burden, suggesting that C. trachomatis actively suppresses CXCL10. We identified the pathogen-encoded factor responsible for this suppression as the chlamydial protease- or proteasome-like activity factor, CPAF. Further, we applied our modeling approach to other host cytokines in response to C. trachomatis and found evidence that RANTES, another T-cell chemoattractant, is actively suppressed by Chlamydia. However, this observed suppression of RANTES is not mediated by CPAF. Overall, our results demonstrate that CPAF suppresses CXCL10 to evade the host cytokine response and that modeling of cellular infection parameters can reveal previously unrecognized facets of host-pathogen interactions.

Place, publisher, year, edition, pages
Nature Publishing Group, 2020
National Category
Microbiology in the medical area Medical Genetics
Identifiers
urn:nbn:se:umu:diva-181818 (URN)10.1038/s41598-020-75129-y (DOI)000615370600001 ()33106516 (PubMedID)2-s2.0-85093978642 (Scopus ID)
Available from: 2021-03-26 Created: 2021-03-26 Last updated: 2022-09-15Bibliographically approved
Sixt, B. S., Núñez-Otero, C., Kepp, O., Valdivia, R. H. & Kroemer, G. (2019). Chlamydia trachomatis fails to protect its growth niche against pro-apoptotic insults. Cell Death and Differentiation, 26(8), 1485-1500
Open this publication in new window or tab >>Chlamydia trachomatis fails to protect its growth niche against pro-apoptotic insults
Show others...
2019 (English)In: Cell Death and Differentiation, ISSN 1350-9047, E-ISSN 1476-5403, Vol. 26, no 8, p. 1485-1500Article in journal (Refereed) Published
Abstract [en]

Chlamydia trachomatis is an obligate intracellular bacterial agent responsible for ocular infections and sexually transmitted diseases. It has been postulated that Chlamydia inhibits apoptosis in host cells to maintain an intact replicative niche until sufficient infectious progeny can be generated. Here we report that, while cells infected with C. trachomatis are protected from apoptosis at early and mid-stages of infection, they remain susceptible to the induction of other cell death modalities. By monitoring the fate of infected cells by time-lapse video microscopy and by analyzing host plasma membrane integrity and the activity of caspases, we determined that C. trachomatis-infected cells exposed to pro-apoptotic stimuli predominately died by a mechanism resembling necrosis. This necrotic death of infected cells occurred with kinetics similar to the induction of apoptosis in uninfected cells, indicating that C. trachomatis fails to considerably prolong the lifespan of its host cell when exposed to pro-apoptotic insults. Inhibitors of bacterial protein synthesis partially blocked necrotic death of infected cells, suggesting that the switch from apoptosis to necrosis relies on an active contribution of the bacteria. Tumor necrosis factor alpha (TNF-α)-mediated induction of necrosis in cells infected with C. trachomatis was not dependent on canonical regulators of necroptosis, such as RIPK1, RIPK3, or MLKL, yet was blocked by inhibition or depletion of CASP8. These results suggest that alternative signaling pathways regulate necrotic death in the context of C. trachomatis infections. Finally, consistent with the inability of C. trachomatis to preserve host cell viability, necrosis resulting from pro-apoptotic conditions significantly impaired production of infectious progeny. Taken together, our findings suggest that Chlamydia's anti-apoptotic activities are not sufficient to protect the pathogen's replicative niche.

Place, publisher, year, edition, pages
Nature Publishing Group, 2019
National Category
Microbiology in the medical area
Identifiers
urn:nbn:se:umu:diva-153979 (URN)10.1038/s41418-018-0224-2 (DOI)000480645800009 ()30375511 (PubMedID)2-s2.0-85055968143 (Scopus ID)
Available from: 2018-12-11 Created: 2018-12-11 Last updated: 2023-03-24Bibliographically approved
Filcek, K., Vielfort, K., Muraleedharan, S., Henriksson, J., Valdivia, R., Bavoil, P. & Sixt, B. S. (2019). Insertional mutagenesis in the zoonotic pathogen Chlamydia caviae. PLOS ONE, 14(11), Article ID e0224324.
Open this publication in new window or tab >>Insertional mutagenesis in the zoonotic pathogen Chlamydia caviae
Show others...
2019 (English)In: PLOS ONE, E-ISSN 1932-6203, Vol. 14, no 11, article id e0224324Article in journal (Refereed) Published
Abstract [en]

The ability to introduce targeted genetic modifications in microbial genomes has revolutionized our ability to study the role and mode of action of individual bacterial virulence factors. Although the fastidious lifestyle of obligate intracellular bacterial pathogens poses a technical challenge to such manipulations, the last decade has produced significant advances in our ability to conduct molecular genetic analysis in Chlamydia trachomatis, a major bacterial agent of infertility and blindness. Similar approaches have not been established for the closely related veterinary Chlamydia spp., which cause significant economic damage, as well as rare but potentially life-threatening infections in humans. Here we demonstrate the feasibility of conducting site-specific mutagenesis for disrupting virulence genes in Ccaviae, an agent of guinea pig inclusion conjunctivitis that was recently identified as a zoonotic agent in cases of severe community-acquired pneumonia. Using this approach, we generated Ccaviae mutants deficient for the secreted effector proteins IncA and SinC. We demonstrate that Ccaviae IncA plays a role in mediating fusion of the bacteria-containing vacuoles inhabited by Ccaviae. Moreover, using a chicken embryo infection model, we provide first evidence for a role of SinC in Ccaviae virulence in vivo.

Place, publisher, year, edition, pages
Public Library of Science, 2019
National Category
Microbiology Infectious Medicine
Research subject
Microbiology
Identifiers
urn:nbn:se:umu:diva-169550 (URN)10.1371/journal.pone.0224324 (DOI)000532694400023 ()31697687 (PubMedID)2-s2.0-85074644319 (Scopus ID)
Available from: 2020-04-06 Created: 2020-04-06 Last updated: 2023-04-24Bibliographically approved
Projects
Illuminating the hidden power of cell-autonomous immunity ? a molecular genetic approach [2018-02286_VR]; Umeå University
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-5607-8902

Search in DiVA

Show all publications