scholarly journals Extrusions promote engulfment and Chlamydia survival within macrophages

2016 ◽  
Author(s):  
Meghan Zuck ◽  
Tisha C Ellis ◽  
Anthony Venida ◽  
Kevin Hybiske
Keyword(s):  
Immune Responses ◽  
Host Cell ◽  
Membrane Structure ◽  
Functional Role ◽  
Host Cells ◽  
Obligate Intracellular Bacterium ◽  
Obligate Intracellular ◽  
Primary Bone ◽  
New Hosts ◽  
Primary Bone Marrow

All obligate intracellular pathogens must exit their host cells in order to propagate and survive as a species; the precise strategies they use have a direct impact on their ability to disseminate within a host, transmit to new hosts, and engage or avoid immune responses. The obligate intracellular bacterium Chlamydia trachomatis exits the host cell by two distinct exit strategies, lysis and extrusion. Despite being equally active pathways, lysis and extrusion differ greatly in their mechanisms. The defining characteristics of extrusions, and advantages gained by Chlamydia within this unique double-membrane structure are not well understood. Here, we present data that defines extrusions as being largely devoid of host organelles, comprised mostly of Chlamydia elementary bodies, and containing phosphatidylserine on the outer surface of the extrusion membrane. Towards defining a functional role for extrusions in Chlamydia pathogenesis, we demonstrate that extrusions confer significant infectious advantages for Chlamydia by serving as transient, intracellular-like niches for extracellular Chlamydia, as compared to Chlamydia that would otherwise exit by lysing the host cell. In addition to enhanced survival outside of the host cell, we report the key discovery that chlamydial extrusions can be engulfed by primary bone marrow-derived macrophages, after which they provide a protective microenvironment for Chlamydia. Extrusion-derived Chlamydia were able to stave off macrophage based killing beyond 8 h, and culminated in the release of infectious EB from the macrophage. Based on these findings, we propose a model in which a major outcome of Chlamydia exiting epithelial cells inside extrusions is to hijack macrophages as vehicles for dissemination within the host.

scholarly journals Coxiella burnetiiType 4B Secretion System-dependent manipulation of endolysosomal maturation is required for bacterial growth

2019 ◽  
Author(s):  
Dhritiman Samanta ◽  
Tatiana M. Clemente ◽  
Stacey D. Gilk
Keyword(s):  
Host Cell ◽  
Secretion System ◽  
Intracellular Bacterium ◽  
Host Cells ◽  
Acidic Ph ◽  
Obligate Intracellular Bacterium ◽  
Cell Infection ◽  
Obligate Intracellular ◽  
Endosomal Acidification ◽  
Infected Cells

AbstractUpon host cell infection, the obligate intracellular bacteriumC. burnetiiresides and multiplies within theCoxiella–ContainingVacuole (CCV). The nascent CCV progresses through the endosomal maturation pathway into a phagolysosome, acquiring lysosomal markers as well as acidic pH and active proteases and hydrolases. Approximately 24-48 hours post infection, heterotypic fusion between the CCV and host endosomes/lysosomes leads to CCV expansion and subsequent bacterial replication in the mature CCV. Initial CCV acidification is required to activateC. burnetiimetabolism and the Type 4B Secretion System (T4BSS), which secretes effector proteins required for CCV maturation. However, we recently found that the mature CCV is less acidic (pH~5.2) than lysosomes (pH~4.8). Further, CCV acidification to pH~4.8 causesC. burnetiilysis, suggestingC. burnetiiactively regulates CCV pH. Because heterotypic fusion with host endosomes/lysosomes may influence CCV pH, we investigated endosomal maturation in cells infected with wildtype (WT) or T4BSS mutant (ΔdotA)C. burnetii. We observed significantly fewer LAMP1-positive lysosomes, along with less acidic “mature” endosomes (pH~5.8), in WT-infected cells, compared to mock or ΔdotA-infected cells. Further, while endosomes progressively acidified from the periphery (pH~5.5) to the perinuclear area (pH~4.7) in both mock and ΔdotA-infected cells, endosomes did not acidify beyond pH~5.2 in WT-infected cells, indicating that theC. burnetiiT4BSS inhibits endosomal maturation. Finally, increasing the number of acidic lysosomes by overexpressing the transcription factor EB inhibitedC. burnetiigrowth, indicating lysosomes are detrimental toC. burnetii. Overall, our data suggest thatC. burnetiiregulates CCV pH, possibly by reducing the number of host lysosomes available for heterotypic fusion.Author summaryThe obligate intracellular bacteriumCoxiella burnetiicauses human Q fever, which manifests as a flu-like illness but can develop into a life-threatening and difficult to treat endocarditis.C. burnetii,in contrast to many other intracellular bacteria, thrives within a lysosome-like vacuole in host cells. However, we previously found that theC. burnetiivacuole is not as acidic as lysosomes and increased acidification kills the bacteria, suggesting thatC. burnetiiregulates the pH of its vacuole. Here, we discovered thatC. burnetiiblocks endosomal maturation and acidification during host cell infection, resulting in fewer lysosomes in the host cell. Moreover, increasing lysosomes in the host cells blockedC. burnetiigrowth. Together, our study suggests thatC. burnetiiregulates vacuole acidity and blocks endosomal acidification in order to produce a permissive intracellular niche.

scholarly journals Developmental differentiation in a cytoplasm-dwelling obligate intracellular bacterium

2020 ◽  
Author(s):  
Suparat Giengkam ◽  
Jantana Wongsantichon ◽  
Sharanjeet Atwal ◽  
Yanin Jaiyen ◽  
Wah Ing Goh ◽  
...  
Keyword(s):  
Host Cell ◽  
Metabolic Activity ◽  
Model System ◽  
Intracellular Bacterium ◽  
Host Cells ◽  
Orientia Tsutsugamushi ◽  
Obligate Intracellular Bacterium ◽  
New Model ◽  
Obligate Intracellular ◽  
Developmental Differentiation

AbstractDevelopmental differentiation has been described for several vacuole-dwelling obligate intracellular bacteria but never for an obligate intracellular bacterium that resides in the cytoplasm. Here, we show that the cytoplasm-dwelling obligate intracellular bacterium Orientia tsutsugamushi (Ot) exists in five distinct subpopulations. We show that Ot differentiates into a distinct, metabolically inactive, extracellular state upon budding from the surface of host cells and that this stage is preceded by a surface-associated maturation stage. We identify proteins that are differentially expressed in intracellular, replicative bacteria and extracellular, metabolically inactive bacteria. Metabolic activity resumes rapidly upon entry into the cytoplasm and is triggered by the host cell reducing environment. This example of developmental differentiation in a species of Rickettsiaceae provides a new model system for studying synchronized differentiation in a bacterium that has a minimal genome and where the interactions between bacterium and host cell are more direct than they are for bacteria separated from the eukaryote cell host by a vacuolar membrane.Author SummaryScrub typhus is a life-threatening human infection that is caused by the bacterium Orientia tsutsugamushi and spread by mites. Although the disease is estimated to affect at least one million people annually and is often fatal, the infectious agent is much less well understood than many other pathogens. O. tsutsugamushi is an intracellular bacterium that can only grow and divide within eukaryotic cells. During infection, it is found primarily in the cells that make up the lining of blood vessels and in certain immune cell types. O. tsutsugamushi bacteria can remain inside a single infected cell for seven days or more before budding out. The ways in which the bacterium itself changes during the course of an intracellular infection cycle have not been studied. In the current work, we used a range of techniques to show that O. tsutsugamushi differentiates into five distinct subpopulations, and that these are associated with measurable differences in metabolic activity, replication and infectivity. This work opens new avenues of research into the regulation and mechanisms of differentiation of O. tsutsugamushi, which could lead to improved diagnosis and treatments. It also provides a new model system for studying fundamental questions about bacterial development.

scholarly journals A streamlined method for transposon mutagenesis ofRickettsia parkeriyields numerous mutations that impact infection

2018 ◽  
Author(s):  
Rebecca L. Lamason ◽  
Natasha M. Kafai ◽  
Matthew D. Welch
Keyword(s):  
Host Cell ◽  
Virulence Factors ◽  
Vascular Endothelial Cells ◽  
Spotted Fever ◽  
Transposon Mutagenesis ◽  
Host Cells ◽  
Spotted Fever Group ◽  
Loss Of Function ◽  
Rickettsia Parkeri ◽  
Obligate Intracellular

AbstractThe rickettsiae are obligate intracellular alphaproteobacteria that exhibit a complex infectious life cycle in both arthropod and mammalian hosts. As obligate intracellular bacteria,Rickettsiaare highly adapted to living inside a variety of host cells, including vascular endothelial cells during mammalian infection. Although it is assumed that the rickettsiae produce numerous virulence factors that usurp or disrupt various host cell pathways, they have been challenging to genetically manipulate to identify the key bacterial factors that contribute to infection. Motivated to overcome this challenge, we sought to expand the repertoire of available rickettsial loss-of-function mutants, using an improvedmariner-based transposon mutagenesis scheme. Here, we present the isolation of over 100 transposon mutants in the spotted fever group speciesRickettsia parkeri. These mutants targeted genes implicated in a variety of pathways, including bacterial replication and metabolism, hypothetical proteins, the type IV secretion system, as well as factors with previously established roles in host cell interactions and pathogenesis. Given the need to identify critical virulence factors, forward genetic screens such as this will provide an excellent platform to more directly investigate rickettsial biology and pathogenesis.

scholarly journals Toxoplasma gondii Development of Its Replicative Niche: in Its Host Cell and Beyond

2014 ◽  
Vol 13 (8) ◽  
pp. 965-976 ◽  
Author(s):  
Ira J. Blader ◽  
Anita A. Koshy
Keyword(s):  
Toxoplasma Gondii ◽  
Host Cell ◽  
Host Cells ◽  
Content Type ◽  
Obligate Intracellular ◽  
Cellular Processes ◽  
High Prevalence ◽  
Life Threatening ◽  
Cell Processes ◽  
Cellular Pathways

ABSTRACTIntracellular pathogens can replicate efficiently only after they manipulate and modify their host cells to create an environment conducive to replication. While diverse cellular pathways are targeted by different pathogens, metabolism, membrane and cytoskeletal architecture formation, and cell death are the three primary cellular processes that are modified by infections.Toxoplasma gondiiis an obligate intracellular protozoan that infects ∼30% of the world's population and causes severe and life-threatening disease in developing fetuses, in immune-comprised patients, and in certain otherwise healthy individuals who are primarily found in South America. The high prevalence ofToxoplasmain humans is in large part a result of its ability to modulate these three host cell processes. Here, we highlight recent work defining the mechanisms by whichToxoplasmainteracts with these processes. In addition, we hypothesize why some processes are modified not only in the infected host cell but also in neighboring uninfected cells.

Invasion of Toxoplasma gondii occurs by active penetration of the host cell

1995 ◽  
Vol 108 (6) ◽  
pp. 2457-2464 ◽  
Author(s):  
J.H. Morisaki ◽  
J.E. Heuser ◽  
L.D. Sibley
Keyword(s):  
Toxoplasma Gondii ◽  
Host Cell ◽  
Tyrosine Phosphorylation ◽  
Host Cells ◽  
The Novel ◽  
Host Proteins ◽  
Host Cell Membrane ◽  
Membrane Ruffling ◽  
Obligate Intracellular ◽  
Obligate Intracellular Parasite

Toxoplasma gondii is an obligate intracellular parasite that infects a wide variety of vertebrate cells including macrophages. We have used a combination of video microscopy and fluorescence localization to examine the entry of Toxoplasma into macrophages and nonphagocytic host cells. Toxoplasma actively invaded host cells without inducing host cell membrane ruffling, actin microfilament reorganization, or tyrosine phosphorylation of host proteins. Invasion occurred rapidly and within 25–40 seconds the parasite penetrated into a tight-fitting vacuole formed by invagination of the plasma membrane. In contrast, during phagocytosis of Toxoplasma, extensive membrane ruffling captured the parasite in a loose-fitting phagosome that formed over a period of 2–4 minutes. Phagocytosis involved both reorganization of the host cytoskeleton and tyrosine phosphorylation of host proteins. In some cases, parasites that were first internalized by phagocytosis, were able to escape from the phagosome by a process analogous to invasion. These studies reveal that active penetration of the host cell by Toxoplasma is fundamentally different from phagocytosis or induced endocytic uptake. The novel ability to penetrate the host cell likely contributes to the capability of Toxoplasma-containing vacuoles to avoid endocytic processing.

scholarly journals Glycosylation of the Major Polar Tube Protein of Encephalitozoon hellem, a Microsporidian Parasite That Infects Humans

2004 ◽  
Vol 72 (11) ◽  
pp. 6341-6350 ◽  
Author(s):  
Yanji Xu ◽  
Peter M. Takvorian ◽  
Ann Cali ◽  
George Orr ◽  
Louis M. Weiss
Keyword(s):  
Host Cell ◽  
Host Cells ◽  
Polar Tube ◽  
Microsporidian Parasite ◽  
Obligate Intracellular ◽  
Species Analysis ◽  
Wide Range ◽  
Mannose Binding ◽  
Microsporidia Species ◽  
Increased Susceptibility

ABSTRACT The microsporidia are ubiquitous, obligate intracellular eukaryotic spore-forming parasites infecting a wide range of invertebrates and vertebrates, including humans. The defining structure of microsporidia is the polar tube, which forms a hollow tube through which the sporoplasm is transferred to the host cell. Research on the molecular and cellular biology of the polar tube has resulted in the identification of three polar tube proteins: PTP1, PTP2, and PTP3. The major polar tube protein, PTP1, accounts for at least 70% of the mass of the polar tube. In the present study, PTP1 was found to be posttranslationally modified. Concanavalin A (ConA) bound to PTP1 and to the polar tube of several different microsporidia species. Analysis of the glycosylation of Encephalitozoon hellem PTP1 suggested that it is modified by O-linked mannosylation, and ConA binds to these O-linked mannose residues. Mannose pretreatment of RK13 host cells decreased their infection by E. hellem, consistent with an interaction between the mannosylation of PTP1 and some unknown host cell mannose-binding molecule. A CHO cell line (Lec1) that is unable to synthesize complex-type N-linked oligosaccharides had an increased susceptibility to E. hellem infection compared to wild-type CHO cells. These data suggest that the O-mannosylation of PTP1 may have functional significance for the ability of microsporidia to invade their host cells.

scholarly journals Role of Bcl-2 Family Members in Caspase-Independent Apoptosis during Chlamydia Infection

2002 ◽  
Vol 70 (1) ◽  
pp. 55-61 ◽  
Author(s):  
Jean-Luc Perfettini ◽  
John C. Reed ◽  
Nicole Israël ◽  
Jean-Claude Martinou ◽  
Alice Dautry-Varsat ◽  
...  
Keyword(s):  
Caspase 3 ◽  
Chlamydia Psittaci ◽  
Host Cells ◽  
Chlamydia Infection ◽  
Caspase Inhibitor ◽  
Obligate Intracellular Bacterium ◽  
Obligate Intracellular ◽  
Infected Cells ◽  
Induced Apoptosis

ABSTRACT Infection with an obligate intracellular bacterium, the Chlamydia trachomatis lymphogranuloma venereum (LGV/L2) strain or the guinea pig inclusion conjunctivitis serovar of Chlamydia psittaci, leads to apoptosis of host cells. The apoptosis is not affected by a broad-spectrum caspase inhibitor, and caspase-3 is not activated in infected cells, suggesting that apoptosis mediated by these two strains of Chlamydia is independent of known caspases. Overexpression of the proapoptotic Bcl-2 family member, Bax, was previously shown to induce caspase-independent apoptosis, and we find that Bax is activated and translocates from the cytosol to the mitochondria in C. psittaci-infected cells. C. psittaci-induced apoptosis is inhibited in host cells overexpressing Bax inhibitor-1 and is inhibited through overexpression of Bcl-2, which blocks both caspase-dependent and -independent apoptosis. As Bax and mitochondria are ideally located to sense stress-related metabolic changes emanating from the interior of an infected cell, it is likely that Bax-dependent apoptosis may also be observed in cells infected with other intracellular pathogens.

Regulation of host cell survival by intracellularPlasmodiumandTheileriaparasites

Parasitology ◽  
2006 ◽  
Vol 132 (S1) ◽  
pp. S49-S60 ◽  
Author(s):  
V. HEUSSLER ◽  
A. STURM ◽  
G. LANGSLEY
Keyword(s):  
Cell Survival ◽  
Host Cell ◽  
Molecular Level ◽  
Cell Transformation ◽  
Life Cycle Stage ◽  
Host Cells ◽  
Host Interactions ◽  
Obligate Intracellular ◽  
The Subject ◽  
Apoptotic Pathways

PlasmodiumandTheileriaparasites are obligate intracellular protozoa of the phylum Apicomplexa.Theileriainfection of bovine leukocytes induces transformation of host cells and infected leukocytes can be kept indefinitely in culture.Theileria-dependent host cell transformation has been the subject of interest for many years and the molecular basis of this unique phenomenon is quite well understood. The equivalent life cycle stage ofPlasmodiumis the infection of mammalian hepatocytes, where parasites reside for 2–7 days depending on the species. Some of the molecular details of parasite-host interactions inP. berghei-infected hepatocytes have emerged only very recently. Similar to what has been shown forTheileria-infected leukocytes these data suggest that malaria parasites within hepatocytes also protect their host cell from programmed cell death. However, the strategies employed to inhibit host cell apoptotic pathways appear to be different to those used byTheileria. This review discusses similarities and differences at the molecular level ofPlasmodium- andTheileria-induced regulation of the host cell survival machinery.

scholarly journals Phospholipid Composition of PurifiedChlamydia trachomatis Mimics That of the Eucaryotic Host Cell

1998 ◽  
Vol 66 (8) ◽  
pp. 3727-3735 ◽  
Author(s):  
Grant M. Hatch ◽  
Grant McClarty
Keyword(s):  
Host Cell ◽  
Phospholipid Composition ◽  
Brefeldin A ◽  
Host Cells ◽  
Cho Cell ◽  
Experimental Conditions ◽  
Obligate Intracellular ◽  
Wide Range ◽  
Host Cell Surface ◽  
Cellular Phospholipid

ABSTRACT Chlamydia trachomatis is an obligate intracellular eubacterial parasite capable of infecting a wide range of eucaryotic host cells. Purified chlamydiae contain several lipids typically found in eucaryotes, and it has been established that eucaryotic lipids are transported from the host cell to the parasite. In this report, we examine the phospholipid composition of C. trachomatispurified from host cells grown under a variety of conditions in which the cellular phospholipid composition was altered. A mutant CHO cell line, with a thermolabile CDP-choline synthetase, was used to show that decreased host cell phosphatidylcholine levels had no significant effect on C. trachomatis growth. However, less phosphatidylcholine was transported to the parasite and purified elementary bodies contained decreased levels of phosphatidylcholine. Brefeldin A, fumonisin B1, and exogenous sphingomyelinase were used to alter levels of host cell sphingomyelin. None of the agents had a significant effect on C. trachomatisreplication. Treatment with fumonisin B1 and exogenous sphingomyelinase resulted in decreased levels of host cell sphingomyelin. This had no effect on glycerophospholipid trafficking to chlamydiae; however, sphingomyelin trafficking was reduced and elementary bodies purified from treated cells had reduced sphingomyelin content. Exposure to brefeldin A, which had no adverse effect on chlamydia growth, resulted in an increase in cellular levels of sphingomyelin and a concomitant increase in the amount of sphingomyelin in purified chlamydiae. Under the experimental conditions used, brefeldin A treatment had only a small effect on sphingomyelin trafficking to the host cell surface or to C. trachomatis. Thus, the final phospholipid composition of purified C. trachomatis mimics that of the host cell in which it is grown.

scholarly journals Coxiella burnetii Inhibits Activation of Host Cell Apoptosis through a Mechanism That Involves Preventing Cytochrome c Release from Mitochondria

2007 ◽  
Vol 75 (11) ◽  
pp. 5282-5289 ◽  
Author(s):  
Anja Lührmann ◽  
Craig R. Roy
Keyword(s):  
Cell Death ◽  
Host Cell ◽  
Coxiella Burnetii ◽  
Mammalian Cells ◽  
Q Fever ◽  
Host Cells ◽  
Intracellular Pathogen ◽  
Obligate Intracellular ◽  
Cell Death Pathway ◽  
Obligate Intracellular Pathogen

ABSTRACT Coxiella burnetii is an obligate intracellular pathogen and the etiological agent of the human disease Q fever. C. burnetii infects mammalian cells and then remodels the membrane-bound compartment in which it resides into a unique lysosome-derived organelle that supports bacterial multiplication. To gain insight into the mechanisms by which C. burnetii is able to multiply intracellularly, we examined the ability of host cells to respond to signals that normally induce apoptosis. Our data show that mammalian cells infected with C. burnetii are resistant to apoptosis induced by staurosporine and UV light. C. burnetii infection prevented caspase 3/7 activation and limited fragmentation of the host cell nucleus in response to agonists that induce apoptosis. Inhibition of bacterial protein synthesis reduced the antiapoptotic effect that C. burnetii exerted on infected host cells. Inhibition of apoptosis in C. burnetii-infected cells did not correlate with the degradation of proapoptotic BH3-only proteins involved in activation of the intrinsic cell death pathway; however, cytochrome c release from mitochondria was diminished in cells infected with C. burnetii upon induction of apoptosis. These data indicate that C. burnetii can interfere with the intrinsic cell death pathway during infection by producing proteins that either directly or indirectly prevent release of cytochrome c from mitochondria. It is likely that inhibition of apoptosis by C. burnetii represents an important virulence property that allows this obligate intracellular pathogen to maintain host cell viability despite inducing stress that would normally activate the intrinsic death pathway.

Sign in / Sign up

Export Citation Format

Share Document