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 Intraspecies Competition in Serratia marcescens Is Mediated by Type VI-Secreted Rhs Effectors and a Conserved Effector-Associated Accessory Protein

2015 ◽  
Vol 197 (14) ◽  
pp. 2350-2360 ◽  
Author(s):  
Juliana Alcoforado Diniz ◽  
Sarah J. Coulthurst
Keyword(s):  
Serratia Marcescens ◽  
Secretion System ◽  
Effector Proteins ◽  
Target Cells ◽  
Primary Role ◽  
Bacterial Cells ◽  
Type Vi Secretion System ◽  
Content Type ◽  
Type Vi Secretion ◽  
Intraspecies Competition

ABSTRACTThe type VI secretion system (T6SS) is widespread in Gram-negative bacteria and can deliver toxic effector proteins into eukaryotic cells or competitor bacteria. Antibacterial T6SSs are increasingly recognized as key mediators of interbacterial competition and may contribute to the outcome of many polymicrobial infections. Multiple antibacterial effectors can be delivered by these systems, with diverse activities against target cells and distinct modes of secretion. Polymorphic toxins containing Rhs repeat domains represent a recently identified and as-yet poorly characterized class of T6SS-dependent effectors. Previous work had revealed that the potent antibacterial T6SS of the opportunistic pathogenSerratia marcescenspromotes intraspecies as well as interspecies competition (S. L. Murdoch, K. Trunk, G. English, M. J. Fritsch, E. Pourkarimi, and S. J. Coulthurst, J Bacteriol 193:6057–6069, 2011,http://dx.doi.org/10.1128/JB.05671-11). In this study, two new Rhs family antibacterial effectors delivered by this T6SS have been identified. One of these was shown to act as a DNase toxin, while the other contains a novel, cytoplasmic-acting toxin domain. Importantly, usingS. marcescens, it has been demonstrated for the first time that Rhs proteins, rather than other T6SS-secreted effectors, can be the primary determinant of intraspecies competition. Furthermore, a new family of accessory proteins associated with T6SS effectors has been identified, exemplified byS. marcescensEagR1, which is specifically required for deployment of its associated Rhs effector. Together, these findings provide new insight into how bacteria can use the T6SS to deploy Rhs-family effectors and mediate different types of interbacterial interactions.IMPORTANCEInfectious diseases caused by bacterial pathogens represent a continuing threat to health and economic prosperity. To counter this threat, we must understand how such organisms survive and prosper. The type VI secretion system is a weapon that many pathogens deploy to compete against rival bacterial cells by injecting multiple antibacterial toxins into them. The ability to compete is vital considering that bacteria generally live in mixed communities. We aimed to identify new toxins and understand their deployment and role in interbacterial competition. We describe two new type VI secretion system-delivered toxins of the Rhs class, demonstrate that this class can play a primary role in competition between closely related bacteria, and identify a new accessory factor needed for their delivery.

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 Diversification of the Type VI Secretion System in Agrobacteria

mBio ◽  
2021 ◽  
Author(s):  
Chih-Feng Wu ◽  
Alexandra J. Weisberg ◽  
Edward W. Davis ◽  
Lin Chou ◽  
Surtaz Khan ◽  
...  
Keyword(s):  
Secretion System ◽  
Effector Proteins ◽  
Gram Negative Bacteria ◽  
Type Vi Secretion System ◽  
Gram Negative ◽  
Bacterial Interactions ◽  
Type Vi Secretion

The T6SS is used by several taxa of Gram-negative bacteria to secrete toxic effector proteins to attack others. Diversification of effector collections shapes bacterial interactions and impacts the health of hosts and ecosystems in which bacteria reside.

scholarly journals A new family of Type VI secretion system-delivered effector proteins displays ion-selective pore-forming activity

2019 ◽  
Author(s):  
Giuseppina Mariano ◽  
Katharina Trunk ◽  
David J. Williams ◽  
Laura Monlezun ◽  
Henrik Strahl ◽  
...  
Keyword(s):  
Effector Proteins ◽  
Type Vi Secretion System ◽  
Secretion Systems ◽  
New Family ◽  
Type Vi Secretion ◽  
Outer Membrane Permeability ◽  
Polymicrobial Communities ◽  
Bacterial Effectors

AbstractType VI secretion systems (T6SSs) are nanomachines widely used by bacteria to compete with rivals. T6SSs deliver multiple toxic effector proteins directly into neighbouring cells and play key roles in shaping diverse polymicrobial communities. A number of families of T6SS-dependent anti-bacterial effectors have been characterised, however the mode of action of others remains unknown. Here we report that Ssp6, an anti-bacterial effector delivered by theSerratia marcescensT6SS, is an ion-selective pore-forming toxin.In vivo, Ssp6 inhibits growth by causing depolarisation of the inner membrane of intoxicated cells and also leads to increased outer membrane permeability, whilst reconstruction of Ssp6 activityin vitrodemonstrated that it forms cation-selective pores. A survey of bacterial genomes revealed that Ssp6-like effectors are widespread in Enterobacteriaceae and often linked with T6SS genes. We conclude that Ssp6 represents a new family of T6SS-delivered anti-bacterial effectors, further diversifying the portfolio of weapons available for deployment during inter-bacterial conflict.

scholarly journals Bacterial Type VI secretion system could have evolved from co-opted tail sheath tube of bacteriophages

2019 ◽  
Author(s):  
Wenfa Ng
Keyword(s):  
Protein Structure ◽  
Bacterial Genome ◽  
Secretion System ◽  
Gram Negative Bacteria ◽  
Bacterial Cells ◽  
Type Vi Secretion System ◽  
Gram Negative ◽  
Type Vi Secretion ◽  
Phage Tail ◽  
Tail Protein

Bacterial cells utilize a variety of nanomachines to secrete proteins and other molecules into the extracellular environment or target cells. One example is the Type VI secretion system (T6SS) in Gram-negative bacteria. Armed with a contractile mechanism similar to that used by bacteriophages to inject phage DNA into bacterial cells, the T6SS shares a common evolutionary origin with tail associated proteins of bacteriophages at both the structural and protein composition levels. Specifically, proteins constituting the T6SS are known to share provenance with those of the phage tail protein. More importantly, the T6SS is strikingly similar to the phage tail protein in both structure and function. However, a more important question concerns whether the T6SS evolved from the phage tail protein and if yes, what is the mechanism responsible for its development? One possibility could be the co-opt of the tail protein structure by bacterial cells through integration of the genes encoding the tail protein structure within the bacterial genome. In this case, expression of the phage tail protein genes would have resulted in a multiprotein structure without apparent function, which meant that a significant gap remains in comparison with extant T6SS that spans the inner and outer cell membrane of Gram-negative bacteria. While it is desirable to trace the evolutionary steps taken by phage tail proteins to transform into functional T6SS, multiple selection pressure and strong mutational propensity might have erased molecular evidence of such transformation. Hence, the challenge lies in uncovering as much structural and sequence evidence as possible that points to distinct steps in the evolutionary pathway towards T6SS. Structural studies offer a particularly promising route to unentangle the details but it must be augmented with sequence evidence that pins down the molecular events that shape the evolution of the complex multiprotein structure, where clefts from one protein fit into the folds of another in yielding a function that could evolve over eons. Collectively, structural and functional similarity between T6SS and phage tail protein suggests a common evolutionary origin for both macromolecular complexes, which has been established through combined structural, compositional and sequence analysis. But the steps underpinning the transformation of phage tail protein into T6SS remain unclear, which obfuscate understanding of the evolutionary forces that shape the transformation. One possible evolutionary trajectory posits that genes expressing phage tail proteins were co-opted and integrated into the bacterial genome. However, significant gap remains between a phage tail protein structure with unclear function in the cytoplasm and a functional T6SS that spans two bacterial membranes. Future detective work at the structural and sequence level might offer clues to the evolutionary path trodden by a precursor of the bacterial T6SS.

scholarly journals Novel structural components generate distinct type VI secretion system anchoring modes

2020 ◽  
Author(s):  
Patricia Bernal ◽  
R. Christopher D. Furniss ◽  
Selina Fecht ◽  
Rhoda C.Y. Leung ◽  
Livia Spiga ◽  
...  
Keyword(s):  
Functional Diversity ◽  
Distinct Type ◽  
Secretion System ◽  
Effector Proteins ◽  
Structural Components ◽  
Type Vi Secretion System ◽  
Type Vi Secretion ◽  
Sheath Structure

ABSTRACTThe type VI secretion system (T6SS) is a phage-derived contractile nanomachine primarily involved in interbacterial competition. Its pivotal component, TssA, is indispensable for the assembly of the T6SS sheath structure, the contraction of which propels a payload of effector proteins into neighboring cells. Despite their key function, TssA proteins exhibit unexpected diversity and exist in two major forms, a short (TssAS) and a long (TssAL) TssA. Whilst TssAL proteins interact with a partner, called TagA, to anchor the distal end of the extended sheath, the mechanism for the stabilization of TssAS-containing T6SSs remains unknown. Here we discover a novel class of structural components that interact with short TssA proteins and contribute to T6SS assembly by stabilizing the polymerizing sheath from the baseplate. We demonstrate that the presence of these components is important for full sheath extension and optimal firing. Moreover, we show that the pairing of each form of TssA with a different class of sheath stabilization proteins results in T6SS apparatuses that either reside in the cell for a while or fire immediately after sheath extension, thus giving rise to different aggression behaviors. We propose that this functional diversity could contribute to the specialization of the T6SS to suit bacterial lifestyles in diverse environmental niches.

scholarly journals Structure of a bacterial Rhs effector exported by the type VI secretion system

2021 ◽  
Author(s):  
Patrick Guenther ◽  
Dennis Quentin ◽  
Shehryar Ahmad ◽  
Kartik Sachar ◽  
Christos Gatsogiannis ◽  
...  
Keyword(s):  
Bacterial Cell ◽  
Secretion System ◽  
Effector Proteins ◽  
Protein Export ◽  
Spike Protein ◽  
Gram Negative Bacteria ◽  
Structural Elements ◽  
Type Vi Secretion System ◽  
Gram Negative ◽  
Type Vi Secretion

The type VI secretion system (T6SS) is a widespread protein export apparatus found in Gram-negative bacteria. The majority of T6SSs deliver toxic effector proteins into competitor bacteria. Yet, the structure, function, and activation of many of these effectors remains poorly understood. Here, we present the structures of the T6SS effector RhsA from Pseudomonas protegens and its cognate T6SS spike protein, VgrG1, at 3.3 Å resolution. The structures reveal that the rearrangement hotspot (Rhs) repeats of RhsA assemble into a closed anticlockwise β-barrel spiral similar to that found in bacterial insecticidal Tc toxins and in metazoan teneurin proteins. We find that the C-terminal toxin domain of RhsA is autoproteolytically cleaved but remains inside the Rhs ′cocoon′ where, with the exception of three ordered structural elements, most of the toxin is disordered. The N-terminal ′plug′ domain is unique to T6SS Rhs proteins and resembles a champagne cork that seals the Rhs cocoon at one end while also mediating interactions with VgrG1. Interestingly, this domain is also autoproteolytically cleaved inside the cocoon but remains associated with it. We propose that mechanical force is required to remove the cleaved part of the plug, resulting in the release of the toxin domain as it is delivered into a susceptible bacterial cell by the T6SS.

scholarly journals Two PAAR Proteins with Different C-Terminal Extended Domains Have Distinct Ecological Functions in Myxococcus xanthus

2021 ◽  
Vol 87 (9) ◽  
Author(s):  
Ya Liu ◽  
Jianing Wang ◽  
Zheng Zhang ◽  
Feng Wang ◽  
Ya Gong ◽  
...  
Keyword(s):  
Myxococcus Xanthus ◽  
Pathogenic Fungi ◽  
Nuclease Activity ◽  
Secretion System ◽  
Cell Contact ◽  
Bacterial Cells ◽  
Type Vi Secretion System ◽  
Ecological Functions ◽  
Content Type ◽  
Type Vi Secretion

ABSTRACT Bacterial proline-alanine-alanine-arginine (PAAR) proteins are located at the top of the type VI secretion system (T6SS) nanomachine and carry and deliver effectors into neighboring cells. Many PAAR proteins are fused with a variable C-terminal extended domain (CTD). Here, we report that two paar-ctd genes (MXAN_RS08765 and MXAN_RS36995) located in two homologous operons are involved in different ecological functions of Myxococcus xanthus. MXAN_RS08765 inhibited the growth of plant-pathogenic fungi, while MXAN_RS36995 was associated with the colony-merger incompatibility of M. xanthus cells. These two PAAR-CTD proteins were both toxic to Escherichia coli cells, while MXAN_RS08765, but not MXAN_RS36995, was also toxic to Saccharomyces cerevisiae cells. Their downstream adjacent genes, i.e., MXAN_RS08760 and MXAN_RS24590, protected against the toxicities. The MXAN_RS36995 protein was demonstrated to have nuclease activity, and the activity was inhibited by the presence of MXAN_RS24590. Our results highlight that the PAAR proteins diversify the CTDs to play divergent roles in M. xanthus. IMPORTANCE The type VI secretion system (T6SS) is a bacterial cell contact-dependent weapon capable of delivering protein effectors into neighboring cells. The PAAR protein is located at the top of the nanomachine and carries an effector for delivery. Many PAAR proteins are extended with a diverse C-terminal sequence with an unknown structure and function. Here, we report two paar-ctd genes located in two homologous operons involved in different ecological functions of Myxococcus xanthus; one has antifungal activity, and the other is associated with the kin discrimination phenotype. The PAAR-CTD proteins and the proteins encoded by their downstream genes form two toxin-immunity protein pairs. We demonstrated that the C-terminal diversification of the PAAR-CTD proteins enriches the ecological functions of bacterial cells.

scholarly journals When the pandemic opts for the lockdown: Secretion system evolution in the cholera bacterium

2021 ◽  
Vol 8 (3) ◽  
pp. 69-72
Author(s):  
Francis J. Santoriello ◽  
Stefan Pukatzki
Keyword(s):  
Common Ancestor ◽  
Diarrheal Disease ◽  
Secretion System ◽  
Effector Proteins ◽  
Type Vi Secretion System ◽  
Human Gastrointestinal Tract ◽  
Type Vi Secretion ◽  
T4 Bacteriophage ◽  
The Common ◽  
Pandemic Strains

Vibrio cholerae, the causative agent of the diarrheal disease cholera, is a microbe capable of inhabiting two different ecosystems: chitinous surfaces in brackish, estuarine waters and the epithelial lining of the human gastrointestinal tract. V. cholerae defends against competitive microorganisms with a contact-dependent, contractile killing machine called the type VI secretion system (T6SS) in each of these niches. The T6SS resembles an inverted T4 bacteriophage tail and is used to deliver toxic effector proteins into neighboring cells. Pandemic strains of V. cholerae encode a unique set of T6SS effector proteins, which may play a role in pathogenesis or pandemic spread. In our recent study (Santoriello et al. (2020), Nat Commun, doi: 10.1038/s41467-020-20012-7), using genomic and molecular biology tools, we demonstrated that the T6SS island Auxiliary Cluster 3 (Aux3) is unique to pandemic strains of V. cholerae. We went on to show that Aux3 is related to a phage-like element circulating in environmental V. cholerae strains and that two genetic domestication events formed the pandemic Aux3 cluster during the evolution of the pandemic clone. Our findings support two main conclusions: (1) Aux3 evolution from phage-like element to T6SS cluster offers a snapshot of phage domestication in early T6SS evolution and (2) chromosomal maintenance of Aux3 was advantageous to the common ancestor of V. cholerae pandemic strains.

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.

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