scholarly journals A large lipoprotein mediates target specificity for T6SS-dependent killing

2021 ◽  
Author(s):  
Lauren Speare ◽  
Madison Woo ◽  
Anne K Dunn ◽  
Alecia N Septer
Keyword(s):  
Vibrio Fischeri ◽  
Bacterial Species ◽  
Cell Types ◽  
Secretion System ◽  
Type Vi Secretion System ◽  
Type Vi Secretion ◽  
Host Health ◽  
Specificity Factor ◽  
And Function ◽  
Adhesion Factor

Interbacterial competition is prevalent in host-associated microbiota, where it can shape community structure and function, impacting host health in both positive and negative ways. However, the factors that permit bacteria to discriminate among their various neighbors for targeted elimination of competitors remain elusive. We identified a specificity factor in Vibrio species that is used to target specific competitors for elimination. Here, we describe this specificity factor, which is associated with the broadly-distributed type VI secretion system (T6SS), by studying symbiotic Vibrio fischeri, which use the T6SS to compete for colonization sites in their squid host. We demonstrate that a large lipoprotein (TasL) allows V. fischeri cells to restrict T6SS-dependent killing to certain genotypes by selectively integrating competitor cells into aggregates while excluding other cell types. TasL is also required for T6SS-dependent competition within juvenile squid, indicating the adhesion factor is active in the host. Because TasL homologs are found in other host-associated bacterial species, this newly-described specificity factor has the potential to impact microbiome structure within diverse hosts.

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 A New Front in Microbial Warfare—Delivery of Antifungal Effectors by the Type VI Secretion System

2019 ◽  
Vol 5 (2) ◽  
pp. 50 ◽  
Author(s):  
Katharina Trunk ◽  
Sarah J. Coulthurst ◽  
Janet Quinn
Keyword(s):  
Bacterial Species ◽  
Fungal Species ◽  
Secretion System ◽  
Effector Proteins ◽  
Primary Role ◽  
Bacterial Cells ◽  
Type Vi Secretion System ◽  
Type Vi Secretion ◽  
Bacteria And Fungi ◽  
Polymicrobial Communities

Microbes typically exist in mixed communities and display complex synergistic and antagonistic interactions. The Type VI secretion system (T6SS) is widespread in Gram-negative bacteria and represents a contractile nano-machine that can fire effector proteins directly into neighbouring cells. The primary role assigned to the T6SS is to function as a potent weapon during inter-bacterial competition, delivering antibacterial effectors into rival bacterial cells. However, it has recently emerged that the T6SS can also be used as a powerful weapon against fungal competitors, and the first fungal-specific T6SS effector proteins, Tfe1 and Tfe2, have been identified. These effectors act via distinct mechanisms against a variety of fungal species to cause cell death. Tfe1 intoxication triggers plasma membrane depolarisation, whilst Tfe2 disrupts nutrient uptake and induces autophagy. Based on the frequent coexistence of bacteria and fungi in microbial communities, we propose that T6SS-dependent antifungal activity is likely to be widespread and elicited by a suite of antifungal effectors. Supporting this hypothesis, homologues of Tfe1 and Tfe2 are found in other bacterial species, and a number of T6SS-elaborating species have been demonstrated to interact with fungi. Thus, we envisage that antifungal T6SS will shape many polymicrobial communities, including the human microbiota and disease-causing infections.

scholarly journals Extended Loop Region of Hcp1 is Critical for the Assembly and Function of Type VI Secretion System in Burkholderia pseudomallei

2015 ◽  
Vol 5 (1) ◽  
Author(s):  
Yan Ting Lim ◽  
Chacko Jobichen ◽  
Jocelyn Wong ◽  
Direk Limmathurotsakul ◽  
Shaowei Li ◽  
...  
Keyword(s):  
Burkholderia Pseudomallei ◽  
Secretion System ◽  
Type Vi Secretion System ◽  
Loop Region ◽  
Type Vi Secretion ◽  
And Function

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 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 Population dynamics and transcriptomic responses ofPseudomonas aeruginosain a complex laboratory microbial community

2018 ◽  
Author(s):  
Yingying Cheng ◽  
Joey Kuok Hoong Yam ◽  
Zhao Cai ◽  
Yichen Ding ◽  
Lian-Hui Zhang ◽  
...  
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Single Molecule ◽  
Dominant Species ◽  
Bacterial Species ◽  
Secretion System ◽  
Interspecies Interactions ◽  
Type Vi Secretion System ◽  
Mixed Species ◽  
Type Vi Secretion ◽  
Biofilm Community

AbstractPseudomonas aeruginosais one of the dominant species when it co-exists with many other bacterial species in diverse environments. To understand its physiology and interactions with co-existing bacterial species in different conditions, we established physiologically reproducible eighteen-species communities, and found thatP. aeruginosabecame the dominant species in mixed-species biofilm community but not in the planktonic community.P. aeruginosaH1 type VI secretion system was highly induced in the mixed-species biofilm community compare to its mono-species biofilm, which was further demonstrated to play a key role forP. aeruginosato gain fitness over other bacterial species. In addition, the type IV pili and Psl exopolysaccharide were shown to be required forP. aeruginosato compete with other bacterial species in the biofilm community. Our study showed that the physiology ofP. aeruginosais strongly affected by interspecies interactions, and both biofilm determinants and H1 type VI secretion system contribute toP. aeruginosafitness over other species in complex biofilm communities.ImportancePseudomonas aeruginosausually coexists with different bacterial species in natural environment. However, systematic comparative characterization ofP. aeruginosain complex microbial communities with its mono-species communities is lacking. We constructed mixed-species planktonic and biofilm communities consistingP. aeruginosaand seventeen other bacterial species to study the physiology and interaction ofP. aeruginosain complex multiple-species community. A single molecule detection platform, NanoString nCounter®16S rRNA array, was used to shown thatP. aeruginosacan become the dominant species in the biofilm communities while not in the planktonic communities. Comparative transcriptomic analysis and fluorescence-based quantification further revealed thatP. aeruginosaH1 type VI secretion system and biofilm determinants are both required for its fitness in mixed-species biofilm communities.

scholarly journals Analysis of Vibrio cholerae genomes using a novel bioinformatic tool identifies new, active Type VI Secretion System gene clusters

2019 ◽  
Author(s):  
Cristian V. Crisan ◽  
Aroon T. Chande ◽  
Kenneth Williams ◽  
Vishnu Raghuram ◽  
Lavanya Rishishwar ◽  
...  
Keyword(s):  
Vibrio Cholerae ◽  
Bacterial Species ◽  
Gene Clusters ◽  
Secretion System ◽  
Effector Proteins ◽  
Type Vi Secretion System ◽  
Type Vi Secretion ◽  
Bioinformatic Tool ◽  
Immunity Factor ◽  
Auxiliary Gene

AbstractBackgroundLike many bacteria, Vibrio cholerae, which causes fatal cholera, deploys a harpoon-like Type VI Secretion System (T6SS) to compete against other microbes in environmental and host settings. The T6SS punctures adjacent cells and delivers toxic effector proteins that are harmless to bacteria carrying cognate immunity factors. Only four effector/immunity pairs encoded on one large and three auxiliary gene clusters have been characterized from largely clonal, patient-derived strains of V. cholerae.ResultsWe sequenced two dozen V. cholerae strain genomes from diverse sources and developed a novel and adaptable bioinformatic tool based on Hidden Markov Models. We identified two new T6SS auxiliary gene clusters; one, Aux 5, is described here. Four Aux 5 loci are present in the host strain, each with an atypical effector/immunity gene organization. Structural prediction of the putative effector indicated it is a lipase, which we name TleV1 (Type VI lipase effector Vibrio, TleV1). Ectopic TleV1 expression induced toxicity in E. coli, which was rescued by co-expression of the TleV1 immunity factor. A clinical V. cholerae reference strain expressing the Aux 5 cluster used TleV1 to lyse its parental strain upon contact via its T6SS but was unable to kill parental cells expressing TleV1’s immunity factor.ConclusionWe developed a novel bioinformatic method and identified new T6SS gene clusters in V. cholerae. We also showed the TleV1 toxin is delivered in a T6SS-manner by V. cholerae and can lyse other bacterial cells. Our web-based tool may be modified to identify additional novel T6SS genomic loci in diverse bacterial species.

scholarly journals The Type VI Secretion System: A Multipurpose Delivery System with a Phage-Like Machinery

2011 ◽  
Vol 24 (7) ◽  
pp. 751-757 ◽  
Author(s):  
Angela R. Records
Keyword(s):  
Plant Growth Promoting Rhizobacteria ◽  
Secretion System ◽  
Host Cells ◽  
Type Vi Secretion System ◽  
Secretion Systems ◽  
Gram Negative ◽  
Extracellular Milieu ◽  
Type Vi Secretion ◽  
Plant Growth Promoting ◽  
And Function

Whether they live in the soil, drift in the ocean, survive in the lungs of human hosts or reside on the surfaces of leaves, all bacteria must cope with an array of environmental stressors. Bacteria have evolved an impressive suite of protein secretion systems that enable their survival in hostile environments and facilitate colonization of eukaryotic hosts. Collectively, gram-negative bacteria produce six distinct secretion systems that deliver proteins to the extracellular milieu or directly into the cytosol of host cells. The type VI secretion system (T6SS) was discovered recently and is encoded in at least one fourth of all sequenced gram-negative bacterial genomes. T6SS proteins are evolutionarily and structurally related to phage proteins, and it is likely that the T6SS apparatus is reminiscent of phage injection machinery. Most studies of T6SS function have been conducted in the context of host-pathogen interactions. However, the totality of data suggests that the T6SS is a versatile tool with roles in virulence, symbiosis, interbacterial interactions, and antipathogenesis. This review gives a brief history of T6SS discovery and an overview of the pathway's predicted structure and function. Special attention is paid to research addressing the T6SS of plant-associated bacteria, including pathogens, symbionts and plant growth–promoting rhizobacteria.

scholarly journals Genetic Dissection of the Type VI Secretion System inAcinetobacterand Identification of a Novel Peptidoglycan Hydrolase, TagX, Required for Its Biogenesis

mBio ◽  
2016 ◽  
Vol 7 (5) ◽  
Author(s):  
Brent S. Weber ◽  
Seth W. Hennon ◽  
Meredith S. Wright ◽  
Nichollas E. Scott ◽  
Véronique de Berardinis ◽  
...  
Keyword(s):  
Antibacterial Activity ◽  
Acinetobacter Baumannii ◽  
Mutational Analysis ◽  
Bacterial Species ◽  
Secretion System ◽  
Peptidoglycan Hydrolase ◽  
Type Vi Secretion System ◽  
Differential Proteomics ◽  
Genetic Components ◽  
Type Vi Secretion

ABSTRACTThe type VI secretion system (T6SS) is a widespread secretory apparatus produced by Gram-negative bacteria that has emerged as a potent mediator of antibacterial activity during interbacterial interactions. MostAcinetobacterspecies produce a genetically conserved T6SS, although the expression and functionality of this system vary among different strains. Some pathogenicAcinetobacter baumanniistrains activate this secretion system via the spontaneous loss of a plasmid carrying T6SS repressors. In this work, we compared the expression of T6SS-related genes via transcriptome sequencing and differential proteomics in cells with and without the plasmid. This approach, together with the mutational analysis of the T6SS clusters, led to the determination of the genetic components required to elaborate a functional T6SS in the nosocomial pathogenA. baumanniiand the nonpathogenA. baylyi. By constructing a comprehensive combination of mutants with changes in the T6SS-associatedvgrGgenes, we delineated their relative contributions to T6SS function. We further determined the importance of two effectors, including an effector-immunity pair, for antibacterial activity. Our genetic analysis led to the identification of an essential membrane-associated structural component named TagX, which we have characterized as a peptidoglycan hydrolase possessingl,d-endopeptidase activity. TagX shows homology to known bacteriophagel,d-endopeptidases and is conserved in the T6SS clusters of several bacterial species. We propose that TagX is the first identified enzyme that fulfills the important role of enabling the transit of T6SS machinery across the peptidoglycan layer of the T6SS-producing bacterium.IMPORTANCEAcinetobacter baumanniiis one of the most troublesome and least investigated multidrug-resistant bacterial pathogens. We have previously shown thatA. baumanniiemploys a T6SS to eliminate competing bacteria. Here we provide a comprehensive analysis of the components of the T6SS ofAcinetobacter, and our results provide genetic and functional insights into theAcinetobacterT6SS. Through this analysis, we identified a novel peptidoglycan hydrolase, TagX, that is required for biogenesis of the T6SS apparatus. This is the first peptidoglycanase specialized in T6SS function identified in any species. We propose that this enzyme is required for the spatially and temporally regulated digestion of peptidoglycan to allow assembly of the T6SS machinery.

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