scholarly journals Bacterial symbionts use a type VI secretion system to eliminate competitors in their natural host

2018 ◽  
Vol 115 (36) ◽  
pp. E8528-E8537 ◽  
Author(s):  
Lauren Speare ◽  
Andrew G. Cecere ◽  
Kirsten R. Guckes ◽  
Stephanie Smith ◽  
Michael S. Wollenberg ◽  
...  
Keyword(s):  
Intraspecific Competition ◽  
Vibrio Fischeri ◽  
Secretion System ◽  
Dependent Manner ◽  
Light Organ ◽  
Type Vi Secretion System ◽  
Type Vi Secretion ◽  
Natural Isolates ◽  
Physical Mixing

Intraspecific competition describes the negative interaction that occurs when different populations of the same species attempt to fill the same niche. Such competition is predicted to occur among host-associated bacteria but has been challenging to study in natural biological systems. Although many bioluminescentVibrio fischeristrains exist in seawater, only a few strains are found in the light-organ crypts of an individual wild-caughtEuprymna scolopessquid, suggesting a possible role for intraspecific competition during early colonization. Using a culture-based assay to investigate the interactions of differentV. fischeristrains, we found “lethal” and “nonlethal” isolates that could kill or not kill the well-studied light-organ isolate ES114, respectively. The killing phenotype of these lethal strains required a type VI secretion system (T6SS) encoded in a 50-kb genomic island. Multiple lethal and nonlethal strains could be cultured from the light organs of individual wild-caught adult squid. Although lethal strains eliminate nonlethal strains in vitro, two lethal strains could coexist in interspersed microcolonies that formed in a T6SS-dependent manner. This coexistence was destabilized upon physical mixing, resulting in one lethal strain consistently eliminating the other. When juvenile squid were coinoculated with lethal and nonlethal strains, they occupied different crypts, yet they were observed to coexist within crypts when T6SS function was disrupted. These findings, using a combination of natural isolates and experimental approaches in vitro and in the animal host, reveal the importance of T6SS in spatially separating strains during the establishment of host colonization in a natural symbiosis.

scholarly journals Environmental Viscosity Modulates Interbacterial Killing during Habitat Transition

mBio ◽  
2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Lauren Speare ◽  
Stephanie Smith ◽  
Fernanda Salvato ◽  
Manuel Kleiner ◽  
Alecia N. Septer
Keyword(s):  
Intraspecific Competition ◽  
Physical Environment ◽  
Vibrio Fischeri ◽  
Secretion System ◽  
Type Vi Secretion System ◽  
Free Living ◽  
Host Colonization ◽  
Content Type ◽  
Type Vi Secretion ◽  
Habitat Transition

ABSTRACT Symbiotic bacteria use diverse strategies to compete for host colonization sites. However, little is known about the environmental cues that modulate interbacterial competition as they transition between free-living and host-associated lifestyles. We used the mutualistic relationship between Eupyrmna scolopes squid and Vibrio fischeri bacteria to investigate how intraspecific competition is regulated as symbionts move from the seawater to a host-like environment. We recently reported that V. fischeri uses a type VI secretion system (T6SS) for intraspecific competition during host colonization. Here, we investigated how environmental viscosity impacts T6SS-mediated competition by using a liquid hydrogel medium that mimics the viscous host environment. Our data demonstrate that although the T6SS is functionally inactive when cells are grown under low-viscosity liquid conditions similar to those found in seawater, exposure to a host-like high-viscosity hydrogel enhances T6SS expression and sheath formation, activates T6SS-mediated killing in as little as 30 min, and promotes the coaggregation of competing genotypes. Finally, the use of mass spectrometry-based proteomics revealed insights into how cells may prepare for T6SS competition during this habitat transition. These findings, which establish the use of a new hydrogel culture condition for studying T6SS interactions, indicate that V. fischeri rapidly responds to the physical environment to activate the competitive mechanisms used during host colonization. IMPORTANCE Bacteria often engage in interference competition to gain access to an ecological niche, such as a host. However, little is known about how the physical environment experienced by free-living or host-associated bacteria influences such competition. We used the bioluminescent squid symbiont Vibrio fischeri to study how environmental viscosity impacts bacterial competition. Our results suggest that upon transition from a planktonic environment to a host-like environment, V. fischeri cells activate their type VI secretion system, a contact-dependent interbacterial nanoweapon, to eliminate natural competitors. This work shows that competitor cells form aggregates under host-like conditions, thereby facilitating the contact required for killing, and reveals how V. fischeri regulates a key competitive mechanism in response to the physical environment.

scholarly journals The Bacterial Enhancer Binding Protein VasH Promotes Expression of a Type VI Secretion System in Vibrio fischeri during Symbiosis

2020 ◽  
Vol 202 (7) ◽  
Author(s):  
Kirsten R. Guckes ◽  
Andrew G. Cecere ◽  
Amanda L. Williams ◽  
Anjali E. McNeil ◽  
Tim Miyashiro
Keyword(s):  
Vibrio Fischeri ◽  
Binding Protein ◽  
Secretion System ◽  
Light Organ ◽  
Bacterial Symbionts ◽  
Type Vi Secretion System ◽  
Intercellular Interactions ◽  
Content Type ◽  
Type Vi Secretion ◽  
Enhancer Binding Protein

ABSTRACT Vibrio fischeri is a bacterial symbiont that colonizes the light organ of the Hawaiian bobtail squid, Euprymna scolopes. Certain strains of V. fischeri express a type VI secretion system (T6SS), which delivers effectors into neighboring cells that result in their death. Strains that are susceptible to the T6SS fail to establish symbiosis with a T6SS-positive strain within the same location of the squid light organ, which is a phenomenon termed strain incompatibility. This study investigates the regulation of the T6SS in V. fischeri strain FQ-A001. Here, we report that the expression of Hcp, a necessary structural component of the T6SS, depends on the alternative sigma factor σ54 and the bacterial enhancer binding protein VasH. VasH is necessary for FQ-A001 to kill other strains, suggesting that VasH-dependent regulation is essential for the T6SS of V. fischeri to affect intercellular interactions. In addition, this study demonstrates VasH-dependent transcription of hcp within host-associated populations of FQ-A001, suggesting that the T6SS is expressed within the host environment. Together, these findings establish a model for transcriptional control of hcp in V. fischeri within the squid light organ, thereby increasing understanding of how the T6SS is regulated during symbiosis. IMPORTANCE Animals harbor bacterial symbionts with specific traits that promote host fitness. Mechanisms that facilitate intercellular interactions among bacterial symbionts impact which bacterial lineages ultimately establish symbiosis with the host. How these mechanisms are regulated is poorly characterized in nonhuman bacterial symbionts. This study establishes a model for the transcriptional regulation of a contact-dependent killing machine, thereby increasing understanding of mechanisms by which different strains compete while establishing symbiosis.

scholarly journals Temperature and growth phase influence the outer-membrane proteome and the expression of a type VI secretion system in Yersinia pestis

Microbiology ◽  
2009 ◽  
Vol 155 (2) ◽  
pp. 498-512 ◽  
Author(s):  
Rembert Pieper ◽  
Shih-Ting Huang ◽  
Jeffrey M. Robinson ◽  
David J. Clark ◽  
Hamid Alami ◽  
...  
Keyword(s):  
Yersinia Pestis ◽  
Outer Membrane ◽  
Subcellular Fractionation ◽  
Secretion System ◽  
Dependent Manner ◽  
Type Vi Secretion System ◽  
Extracellular Medium ◽  
Type Vi Secretion

Yersinia pestis cells were grown in vitro at 26 and 37 °C, the ambient temperatures of its flea vector and its mammalian hosts, respectively, and subjected to subcellular fractionation. Abundance changes at 26 vs 37 °C were observed for many outer-membrane (OM) proteins. The cell adhesion protein Ail (y1324) and three putative small β-barrel OM proteins (y1795, y2167 and y4083) were strongly increased at 37 °C. The Ail/Lom family protein y1682 (OmpX) was strongly increased at 26 °C. Several porins and TonB-dependent receptors, which control small molecule transport through the OM, were also altered in abundance in a temperature-dependent manner. These marked differences in the composition of the OM proteome are probably important for the adaptation of Y. pestis to its in vivo life stages. Thirteen proteins that appear to be part of an intact type VI secretion system (T6SS) were identified in membrane fractions of stationary-phase cells grown at 26 °C, but not at 37 °C. The corresponding genes are clustered in the Y. pestis KIM gene locus y3658–y3677. The proteins y3674 and y3675 were particularly abundant and co-fractionated in a M r range indicative of participation in a multi-subunit complex. The soluble haemolysin-coregulated protein y3673 was even more abundant. Its release into the extracellular medium was triggered by treatment of Y. pestis cells with trypsin. Proteases and other stress-response-inducing factors may constitute environmental cues resulting in the activation of the T6SS in Y. pestis.

scholarly journals Incompatibility of Vibrio fischeri Strains during Symbiosis Establishment Depends on Two Functionally Redundant hcp Genes

2019 ◽  
Vol 201 (19) ◽  
Author(s):  
Kirsten R. Guckes ◽  
Andrew G. Cecere ◽  
Nathan P. Wasilko ◽  
Amanda L. Williams ◽  
Katherine M. Bultman ◽  
...  
Keyword(s):  
Molecular Mechanisms ◽  
Genetic Factors ◽  
Vibrio Fischeri ◽  
Secretion System ◽  
Light Organ ◽  
Type Vi Secretion System ◽  
Content Type ◽  
Type Vi Secretion ◽  
Different Strains

ABSTRACT Bacteria that have the capacity to fill the same niche will compete with one another for the space and resources available within an ecosystem. Such competition is heightened among different strains of the same bacterial species. Nevertheless, different strains often inhabit the same host. The molecular mechanisms that impact competition between different strains within the same host are poorly understood. To address this knowledge gap, the type VI secretion system (T6SS), which is a mechanism for bacteria to kill neighboring cells, was examined in the marine bacterium Vibrio fischeri. Different strains of V. fischeri naturally colonize the light organ of the bobtail squid Euprymna scolopes. The genome of FQ-A001, a T6SS-positive strain, features two hcp genes that are predicted to encode identical subunits of the T6SS. Coincubation assays showed that either hcp gene is sufficient for FQ-A001 to kill another strain via the T6SS in vitro. Additionally, induction of hcp expression is sufficient to induce killing activity in an FQ-A001 mutant lacking both hcp genes. Squid colonization assays involving inocula of FQ-A001-derived strains mixed with ES114 revealed that both hcp genes must be deleted for FQ-A001 and ES114 to occupy the same space within the light organ. These experimental results provide insight into the genetic factors necessary for the T6SS of V. fischeri to function in vivo, thereby increasing understanding of the molecular mechanisms that impact strain diversity within a host. IMPORTANCE Different bacterial strains compete to occupy the same niche. The outcome of such competition can be affected by the type VI secretion system (T6SS), an intercellular killing mechanism of bacteria. Here an animal-bacterial symbiosis is used as a platform for study of the genetic factors that promote the T6SS-mediated killing of one strain by another. Identification of the molecular determinants of T6SS function in vivo contributes to the understanding of how different strains interact within a host.

scholarly journals The Type VI Secretion System Encoded in Salmonella Pathogenicity Island 19 Is Required for Salmonella enterica Serotype Gallinarum Survival within Infected Macrophages

2013 ◽  
Vol 81 (4) ◽  
pp. 1207-1220 ◽  
Author(s):  
Carlos J. Blondel ◽  
Juan C. Jiménez ◽  
Lorenzo E. Leiva ◽  
Sergio A. Álvarez ◽  
Bernardo I. Pinto ◽  
...  
Keyword(s):  
Salmonella Enterica ◽  
Pathogenicity Island ◽  
Secretion System ◽  
Host Cells ◽  
Economic Losses ◽  
Type Vi Secretion System ◽  
Content Type ◽  
Type Vi Secretion ◽  
Core Components

ABSTRACTSalmonella entericaserotype Gallinarum is the causative agent of fowl typhoid, a disease characterized by high morbidity and mortality that causes major economic losses in poultry production. We have reported thatS. Gallinarum harbors a type VI secretion system (T6SS) encoded inSalmonellapathogenicity island 19 (SPI-19) that is required for efficient colonization of chicks. In the present study, we aimed to characterize the SPI-19 T6SS functionality and to investigate the mechanisms behind the phenotypes previously observedin vivo. Expression analyses revealed that SPI-19 T6SS core components are expressed and produced underin vitrobacterial growth conditions. However, secretion of the structural/secreted components Hcp1, Hcp2, and VgrG to the culture medium could not be determined, suggesting that additional signals are required for T6SS-dependent secretion of these proteins.In vitrobacterial competition assays failed to demonstrate a role for SPI-19 T6SS in interbacterial killing. In contrast, cell culture experiments with murine and avian macrophages (RAW264.7 and HD11, respectively) revealed production of a green fluorescent protein-tagged version of VgrG soon afterSalmonellauptake. Furthermore, infection of RAW264.7 and HD11 macrophages with deletion mutants of SPI-19 or strains with genes encoding specific T6SS core components (clpVandvgrG) revealed that SPI-19 T6SS contributes toS. Gallinarum survival within macrophages at 20 h postuptake. SPI-19 T6SS function was not linked toSalmonella-induced cytotoxicity or cell death of infected macrophages, as has been described for other T6SS. Our data indicate that SPI-19 T6SS corresponds to a novel tool used bySalmonellato survive within host cells.

scholarly journals Promoter Swapping Unveils the Role of the Citrobacter rodentium CTS1 Type VI Secretion System in Interbacterial Competition

2012 ◽  
Vol 79 (1) ◽  
pp. 32-38 ◽  
Author(s):  
Erwan Gueguen ◽  
Eric Cascales
Keyword(s):  
Gene Clusters ◽  
Secretion System ◽  
Citrobacter Rodentium ◽  
Type Vi Secretion System ◽  
Content Type ◽  
Type Vi Secretion ◽  
Artificial Induction ◽  
Release Assay ◽  
Promoter Swapping

ABSTRACT The type VI secretion system (T6SS) is a versatile secretion machine dedicated to various functions in Gram-negative bacteria, including virulence toward eukaryotic cells and antibacterial activity. Activity of T6SS might be followed in vitro by the release of two proteins, Hcp and VgrG, in the culture supernatant. Citrobacter rodentium , a rodent pathogen, harbors two T6SS gene clusters, cts1 and cts2 . Reporter fusion and Hcp release assays suggested that the CTS1 T6SS was not produced or not active. The cts1 locus is composed of two divergent operons. We therefore developed a new vector allowing us to swap the two divergent endogenous promoters by P tac and P BAD using the λ red recombination technology. Artificial induction of both promoters demonstrated that the CTS1 T6SS is functional as shown by the Hcp release assay and confers on C. rodentium a growth advantage in antibacterial competition experiments with Escherichia coli .

scholarly journals TheVibrio choleraeType VI Secretion System Can Modulate Host Intestinal Mechanics to Displace Commensal Gut Bacteria

2017 ◽  
Author(s):  
Savannah L. Logan ◽  
Jacob Thomas ◽  
Jinyuan Yan ◽  
Ryan P. Baker ◽  
Drew S. Shields ◽  
...  
Keyword(s):  
Secretion System ◽  
Effector Proteins ◽  
Target Cells ◽  
Type Vi Secretion System ◽  
Zebrafish Model ◽  
Microbial Competition ◽  
Aeromonas Veronii ◽  
Type Vi Secretion ◽  
Commensal Strain

AbstractHost-associated microbiota help defend against bacterial pathogens; the mechanisms that pathogens possess to overcome this defense, however, remain largely unknown. We developed a zebrafish model and used live imaging to directly study how the human pathogenVibrio choleraeinvades the intestine. The gut microbiota of fish mono-colonized by commensal strainAeromonas veroniiwas displaced byV. choleraeexpressing its Type VI Secretion System (T6SS), a syringe-like apparatus that deploys effector proteins into target cells. Surprisingly, displacement was independent of T6SS-mediated killing ofAeromonas, driven instead by T6SS-induced enhancement of zebrafish intestinal movements that led to expulsion of the resident commensal by the host. Deleting an actin crosslinking domain from the T6SS apparatus returned intestinal motility to normal and thwarted expulsion, without weakeningV. cholerae′sability to killAeromonas in vitro. Our finding that bacteria can manipulate host physiology to influence inter-microbial competition has implications for both pathogenesis and microbiome engineering.

scholarly journals Host Adaptation Predisposes Pseudomonas aeruginosa to Type VI Secretion System-Mediated Predation by the Burkholderia cepacia Complex

2020 ◽  
Author(s):  
Andrew I Perault ◽  
Courtney E Chandler ◽  
David A Rasko ◽  
Robert K Ernst ◽  
Matthew C Wolfgang ◽  
...  
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Burkholderia Cepacia ◽  
Secretion System ◽  
Burkholderia Cenocepacia ◽  
Burkholderia Cepacia Complex ◽  
Dependent Manner ◽  
Type Vi Secretion System ◽  
Secretion Systems ◽  
Type Vi Secretion

SUMMARYPseudomonas aeruginosa (Pa) and Burkholderia cepacia complex (Bcc) species are opportunistic lung pathogens of individuals with cystic fibrosis (CF). While Pa can initiate long-term infections in younger CF patients, Bcc infections only arise in teenagers and adults. Both Pa and Bcc use type VI secretion systems (T6SS) to mediate interbacterial competition. Here, we show that Pa isolates from teenage/adult CF patients, but not those from young CF patients, are outcompeted by the epidemic Bcc isolate Burkholderia cenocepacia strain AU1054 (BcAU1054) in a T6SS-dependent manner. The genomes of susceptible Pa isolates harbor T6SS-abrogating mutations, the repair of which, in some cases, rendered the isolates resistant. Moreover, seven of eight Bcc strains outcompeted Pa strains isolated from the same patients. Our findings suggest that certain mutations that arise as Pa adapts to the CF lung abrogate T6SS activity, making Pa and its human host susceptible to potentially fatal Bcc superinfection.

Citrobacter freundii Activation of NLRP3 Inflammasome via the Type VI Secretion System

2020 ◽  
Author(s):  
Liyun Liu ◽  
Liqiong Song ◽  
Rong Deng ◽  
Ruiting Lan ◽  
Wenjie Jin ◽  
...  
Keyword(s):  
Nlrp3 Inflammasome ◽  
Secretion System ◽  
Interleukin 1Β ◽  
Inflammasome Activation ◽  
Dependent Manner ◽  
Citrobacter Freundii ◽  
Type Vi Secretion System ◽  
Type Vi Secretion ◽  
Tract Infections

Abstract Citrobacter freundii is a significant cause of human infections, responsible for food poisoning, diarrhea, and urinary tract infections. We previously identified a highly cytotoxic and adhesive C. freundii strain CF74 expressing a type VI secretion system (T6SS). In this study, we showed that in mice-derived macrophages, C. freundii CF74 activated the Nucleotide Oligomerization Domain -Like Receptor Family, Pyrin Domain Containing 3(NLRP3) inflammasomes in a T6SS-dependent manner. The C. freundii T6SS activated the inflammasomes mainly through caspase 1 and mediated pyroptosis of macrophages by releasing the cleaved gasdermin-N domain. The CF74 T6SS was required for flagellin-induced interleukin 1β release by macrophages. We further show that the T6SS tail component and effector, hemolysin co-regulation protein-2 (Hcp-2), was necessary and sufficient to trigger NLRP3 inflammasome activation. In vivo, the T6SS played a key role in mediating interleukin 1β secretion and the survival of mice during C. freundii infection in mice. These findings provide novel insights into the role of T6SS in the pathogenesis of C. freundii.

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