51
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Lien YW, Lai EM. Type VI Secretion Effectors: Methodologies and Biology. Front Cell Infect Microbiol 2017; 7:254. [PMID: 28664151 PMCID: PMC5471719 DOI: 10.3389/fcimb.2017.00254] [Citation(s) in RCA: 67] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2017] [Accepted: 05/31/2017] [Indexed: 12/26/2022] Open
Abstract
The type VI secretion system (T6SS) is a nanomachine deployed by many Gram-negative bacteria as a weapon against eukaryotic hosts or prokaryotic competitors. It assembles into a bacteriophage tail-like structure that can transport effector proteins into the environment or target cells for competitive survival or pathogenesis. T6SS effectors have been identified by a variety of approaches, including knowledge/hypothesis-dependent and discovery-driven approaches. Here, we review and discuss the methods that have been used to identify T6SS effectors and the biological and biochemical functions of known effectors. On the basis of the nature and transport mechanisms of T6SS effectors, we further propose potential strategies that may be applicable to identify new T6SS effectors.
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Affiliation(s)
- Yun-Wei Lien
- Institute of Plant and Microbial Biology, Academia SinicaTaipei, Taiwan.,Department of Plant Pathology and Microbiology, National Taiwan UniversityTaipei, Taiwan
| | - Erh-Min Lai
- Institute of Plant and Microbial Biology, Academia SinicaTaipei, Taiwan.,Department of Plant Pathology and Microbiology, National Taiwan UniversityTaipei, Taiwan
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52
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Ma J, Sun M, Dong W, Pan Z, Lu C, Yao H. PAAR-Rhs proteins harbor various C-terminal toxins to diversify the antibacterial pathways of type VI secretion systems. Environ Microbiol 2017; 19:345-360. [PMID: 27871130 DOI: 10.1111/1462-2920.13621] [Citation(s) in RCA: 62] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2016] [Revised: 10/05/2016] [Accepted: 11/10/2016] [Indexed: 11/27/2022]
Abstract
The type VI secretion system (T6SS) of bacteria plays a key role in competing for specific niches by the contact-dependent killing of competitors. Recently, Rhs proteins with polymorphic C-terminal toxin-domains that inhibit or kill neighboring cells were identified. In this report, we identified a novel Rhs with an MPTase4 (Metallopeptidase-4) domain (designated as Rhs-CT1) that showed an antibacterial effect via T6SS in Escherichia coli. We managed to develop a specific strategy by matching the diagnostic domain-architecture of Rhs-CT1 (Rhs with an N-terminal PAAR-motif and a C-terminal toxin domain) for effector retrieval and discovered a series of Rhs-CTs in E. coli. Indeed, the screened Rhs-CT3 with a REase-3 (Restriction endonuclease-3) domain also mediated interbacterial antagonism. Further analysis revealed that vgrGO1 and eagR/DUF1795 (upstream of rhs-ct) were required for the delivery of Rhs-CTs, suggesting eagR as a potential T6SS chaperone. In addition to chaperoned Rhs-CTs, neighborless Rhs-CTs could be classified into a distinct family (Rhs-Nb) sharing close evolutionary relationship with T6SS2-Rhs (encoded in the T6SS2 cluster of E. coli). Notably, the Rhs-Nb-CT5 was confirmed bioinformatically and experimentally to mediate interbacterial antagonism via Hcp2B-VgrG2 module. In a further retrieval analysis, we discovered various toxin/immunity pairs in extensive bacterial species that could be systematically classified into eight referential clans, suggesting that Rhs-CTs greatly diversify the antibacterial pathways of T6SS.
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Affiliation(s)
- Jiale Ma
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, China.,Ministry of Agriculture, Key Lab of Animal Bacteriology, Nanjing, 210095, China
| | - Min Sun
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, China.,Ministry of Agriculture, Key Lab of Animal Bacteriology, Nanjing, 210095, China
| | - Wenyang Dong
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, China.,Ministry of Agriculture, Key Lab of Animal Bacteriology, Nanjing, 210095, China
| | - Zihao Pan
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, China.,Ministry of Agriculture, Key Lab of Animal Bacteriology, Nanjing, 210095, China
| | - Chengping Lu
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, China.,Ministry of Agriculture, Key Lab of Animal Bacteriology, Nanjing, 210095, China
| | - Huochun Yao
- College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, China.,Ministry of Agriculture, Key Lab of Animal Bacteriology, Nanjing, 210095, China
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Abstract
Bacterial pathogens utilize a multitude of methods to invade mammalian hosts, damage tissue sites, and thwart the immune system from responding. One essential component of these strategies for many bacterial pathogens is the secretion of proteins across phospholipid membranes. Secreted proteins can play many roles in promoting bacterial virulence, from enhancing attachment to eukaryotic cells, to scavenging resources in an environmental niche, to directly intoxicating target cells and disrupting their functions. Many pathogens use dedicated protein secretion systems to secrete virulence factors from the cytosol of the bacteria into host cells or the host environment. In general, bacterial protein secretion apparatuses can be divided into classes, based on their structures, functions, and specificity. Some systems are conserved in all classes of bacteria and secrete a broad array of substrates, while others are only found in a small number of bacterial species and/or are specific to only one or a few proteins. In this chapter, we review the canonical features of several common bacterial protein secretion systems, as well as their roles in promoting the virulence of bacterial pathogens. Additionally, we address recent findings that indicate that the innate immune system of the host can detect and respond to the presence of protein secretion systems during mammalian infection.
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54
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Bröms JE, Meyer L, Sjöstedt A. A mutagenesis-based approach identifies amino acids in the N-terminal part of Francisella tularensis IglE that critically control Type VI system-mediated secretion. Virulence 2016; 8:821-847. [PMID: 27830989 PMCID: PMC5626337 DOI: 10.1080/21505594.2016.1258507] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
The Gram-negative bacterium Francisella tularensis is the etiological agent of the zoonotic disease tularemia. Its life cycle is characterized by an ability to survive within phagocytic cells through phagosomal escape and replication in the cytosol, ultimately causing inflammasome activation and host cell death. Required for these processes is the Francisella Pathogenicity Island (FPI), which encodes a Type VI secretion system (T6SS) that is active during intracellular infection. In this study, we analyzed the role of the FPI-component IglE, a lipoprotein which we previously have shown to be secreted in a T6SS-dependent manner. We demonstrate that in F. tularensis LVS, IglE is an outer membrane protein. Upon infection of J774 cells, an ΔiglE mutant failed to escape from phagosomes, and subsequently, to multiply and cause cytopathogenicity. Moreover, ΔiglE was unable to activate the inflammasome, to inhibit LPS-stimulated secretion of TNF-α, and showed marked attenuation in the mouse model. In F. novicida, IglE was required for in vitro secretion of IglC and VgrG. A mutagenesis-based approach involving frameshift mutations and alanine substitution mutations within the first ∼ 38 residues of IglE revealed that drastic changes in the sequence of the extreme N-terminus (residues 2-6) were well tolerated and, intriguingly, caused hyper-secretion of IglE during intracellular infection, while even subtle mutations further downstream lead to impaired protein function. Taken together, this study highlights the importance of IglE in F. tularensis pathogenicity, and the contribution of the N-terminus for all of the above mentioned processes.
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Affiliation(s)
- Jeanette E Bröms
- a Department of Clinical Microbiology , Clinical Bacteriology and Laboratory for Molecular Infection Medicine Sweden (MIMS), Umeå University , Umeå , Sweden
| | - Lena Meyer
- a Department of Clinical Microbiology , Clinical Bacteriology and Laboratory for Molecular Infection Medicine Sweden (MIMS), Umeå University , Umeå , Sweden
| | - Anders Sjöstedt
- a Department of Clinical Microbiology , Clinical Bacteriology and Laboratory for Molecular Infection Medicine Sweden (MIMS), Umeå University , Umeå , Sweden
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55
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Socher E, Sticht H. Probing the Structure of the Escherichia coli Periplasmic Proteins HdeA and YmgD by Molecular Dynamics Simulations. J Phys Chem B 2016; 120:11845-11855. [PMID: 27787971 DOI: 10.1021/acs.jpcb.6b06091] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
HdeA and YmgD are structurally homologous proteins in the periplasm of Escherichia coli. HdeA has been shown to represent an acid-activated chaperone, whereas the function of YmgD has not yet been characterized. We performed pH-titrating molecular dynamics simulations (pHtMD) to investigate the structural changes of both proteins and to assess whether YmgD may also exhibit an unfolding behavior similar to that of HdeA. The unfolding pathway of HdeA includes partially unfolded dimer structures, which represent a prerequisite for subsequent dissociation. In contrast to the coupled unfolding and dissociation of HdeA, YmgD displays dissociation of the folded subunits, and the subunits do not undergo significant unfolding even at low pH values. The differences in subunit stability between HdeA and YmgD may be explained by the structural features of helix D, which represents the starting point of unfolding in HdeA. In summary, the present study suggests that YmgD either is not an acid-activated chaperone or, at least, does not require unfolding for activation.
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Affiliation(s)
- Eileen Socher
- Division of Bioinformatics, Institute of Biochemistry, Friedrich-Alexander-University Erlangen-Nürnberg (FAU) , Fahrstraße 17, 91054 Erlangen, Germany
| | - Heinrich Sticht
- Division of Bioinformatics, Institute of Biochemistry, Friedrich-Alexander-University Erlangen-Nürnberg (FAU) , Fahrstraße 17, 91054 Erlangen, Germany
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56
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VgrG C terminus confers the type VI effector transport specificity and is required for binding with PAAR and adaptor-effector complex. Proc Natl Acad Sci U S A 2016; 113:E3931-40. [PMID: 27313214 DOI: 10.1073/pnas.1600428113] [Citation(s) in RCA: 115] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Type VI secretion system (T6SS) is a macromolecular machine used by many Gram-negative bacteria to inject effectors/toxins into eukaryotic hosts or prokaryotic competitors for survival and fitness. To date, our knowledge of the molecular determinants and mechanisms underlying the transport of these effectors remains limited. Here, we report that two T6SS encoded valine-glycine repeat protein G (VgrG) paralogs in Agrobacterium tumefaciens C58 specifically control the secretion and interbacterial competition activity of the type VI DNase toxins Tde1 and Tde2. Deletion and domain-swapping analysis identified that the C-terminal extension of VgrG1 specifically confers Tde1 secretion and Tde1-dependent interbacterial competition activity in planta, and the C-terminal variable region of VgrG2 governs this specificity for Tde2. Functional studies of VgrG1 and VgrG2 variants with stepwise deletion of the C terminus revealed that the C-terminal 31 aa (C31) of VgrG1 and 8 aa (C8) of VgrG2 are the molecular determinants specifically required for delivery of each cognate Tde toxin. Further in-depth studies on Tde toxin delivery mechanisms revealed that VgrG1 interacts with the adaptor/chaperone-effector complex (Tap-1-Tde1) in the absence of proline-alanine-alanine-arginine (PAAR) and the VgrG1-PAAR complex forms independent of Tap-1 and Tde1. Importantly, we identified the regions involved in these interactions. Although the entire C31 segment is required for binding with the Tap-1-Tde1 complex, only the first 15 aa of this region are necessary for PAAR binding. These results suggest that the VgrG1 C terminus interacts sequentially or simultaneously with the Tap-1-Tde1 complex and PAAR to govern Tde1 translocation across bacterial membranes and delivery into target cells for antibacterial activity.
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57
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VgrG and PAAR Proteins Define Distinct Versions of a Functional Type VI Secretion System. PLoS Pathog 2016; 12:e1005735. [PMID: 27352036 PMCID: PMC4924876 DOI: 10.1371/journal.ppat.1005735] [Citation(s) in RCA: 134] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2016] [Accepted: 06/08/2016] [Indexed: 01/19/2023] Open
Abstract
The Type VI secretion system (T6SS) is widespread among bacterial pathogens and acts as an effective weapon against competitor bacteria and eukaryotic hosts by delivering toxic effector proteins directly into target cells. The T6SS utilises a bacteriophage-like contractile machinery to expel a puncturing device based on a tube of Hcp topped with a VgrG spike, which can be extended by a final tip from a PAAR domain-containing protein. Effector proteins are believed to be delivered by specifically associating with particular Hcp, VgrG or PAAR proteins, either covalently ('specialised') or non-covalently ('cargo' effectors). Here we used the T6SS of the opportunistic pathogen Serratia marcescens, together with integratecd genetic, proteomic and biochemical approaches, to elucidate the role of specific VgrG and PAAR homologues in T6SS function and effector specificity, revealing new aspects and unexpected subtleties in effector delivery by the T6SS. We identified effectors, both cargo and specialised, absolutely dependent on a particular VgrG for delivery to target cells, and discovered that other cargo effectors can show a preference for a particular VgrG. The presence of at least one PAAR protein was found to be essential for T6SS function, consistent with designation as a 'core' T6SS component. We showed that specific VgrG-PAAR combinations are required to assemble a functional T6SS and that the three distinct VgrG-PAAR assemblies in S. marcescens exhibit distinct effector specificity and efficiency. Unexpectedly, we discovered that two different PAAR-containing Rhs proteins can functionally pair with the same VgrG protein. Showing that accessory EagR proteins are involved in these interactions, native VgrG-Rhs-EagR complexes were isolated and specific interactions between EagR and cognate Rhs proteins identified. This study defines an essential yet flexible role for PAAR proteins in the T6SS and highlights the existence of distinct versions of the machinery with differential effector specificity and efficiency of target cell delivery.
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58
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Expression, secretion and bactericidal activity of type VI secretion system in Vibrio anguillarum. Arch Microbiol 2016; 198:751-60. [DOI: 10.1007/s00203-016-1236-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2016] [Revised: 04/21/2016] [Accepted: 05/05/2016] [Indexed: 10/21/2022]
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59
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Alcoforado Diniz J, Liu YC, Coulthurst SJ. Molecular weaponry: diverse effectors delivered by the Type VI secretion system. Cell Microbiol 2015; 17:1742-51. [PMID: 26432982 PMCID: PMC4832377 DOI: 10.1111/cmi.12532] [Citation(s) in RCA: 114] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2015] [Revised: 09/22/2015] [Accepted: 09/25/2015] [Indexed: 12/18/2022]
Abstract
The Type VI secretion system is a widespread bacterial nanomachine, used to deliver toxins directly into eukaryotic or prokaryotic target cells. These secreted toxins, or effectors, act on diverse cellular targets, and their action provides the attacking bacterial cell with a significant fitness advantage, either against rival bacteria or eukaryotic host organisms. In this review, we discuss the delivery of diverse effectors by the Type VI secretion system, the modes of action of the so-called 'anti-bacterial' and 'anti-eukaryotic' effectors, the mechanism of self-resistance against anti-bacterial effectors and the evolutionary implications of horizontal transfer of Type VI secretion system-associated toxins. Whilst it is likely that many more effectors remain to be identified, it is already clear that toxins delivered by this secretion system represent efficient weapons against both bacteria and eukaryotes.
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Affiliation(s)
- Juliana Alcoforado Diniz
- Division of Molecular Microbiology, School of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
| | - Yi-Chia Liu
- Division of Molecular Microbiology, School of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
| | - Sarah J Coulthurst
- Division of Molecular Microbiology, School of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
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60
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Gerc AJ, Diepold A, Trunk K, Porter M, Rickman C, Armitage JP, Stanley-Wall NR, Coulthurst SJ. Visualization of the Serratia Type VI Secretion System Reveals Unprovoked Attacks and Dynamic Assembly. Cell Rep 2015; 12:2131-42. [PMID: 26387948 PMCID: PMC4594159 DOI: 10.1016/j.celrep.2015.08.053] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2015] [Revised: 07/24/2015] [Accepted: 08/18/2015] [Indexed: 12/31/2022] Open
Abstract
The Type VI secretion system (T6SS) is a bacterial nanomachine that fires toxic proteins into target cells. Deployment of the T6SS represents an efficient and widespread means by which bacteria attack competitors or interact with host organisms and may be triggered by contact from an attacking neighbor cell as a defensive strategy. Here, we use the opportunist pathogen Serratia marcescens and functional fluorescent fusions of key components of the T6SS to observe different subassemblies of the machinery simultaneously and on multiple timescales in vivo. We report that the localization and dynamic behavior of each of the components examined is distinct, revealing a multi-stage and dynamic assembly process for the T6SS machinery. We also show that the T6SS can assemble and fire without needing a cell contact trigger, defining an aggressive strategy that broadens target range and suggesting that activation of the T6SS is tailored to survival in specific niches.
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Affiliation(s)
- Amy J Gerc
- Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK
| | - Andreas Diepold
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK
| | - Katharina Trunk
- Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK
| | - Michael Porter
- Centre of Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK
| | - Colin Rickman
- Edinburgh Super-Resolution Imaging Consortium, www.esric.org, and Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh EH14 4AS, UK
| | - Judith P Armitage
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK
| | - Nicola R Stanley-Wall
- Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK
| | - Sarah J Coulthurst
- Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK.
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61
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Identification of divergent type VI secretion effectors using a conserved chaperone domain. Proc Natl Acad Sci U S A 2015; 112:9106-11. [PMID: 26150500 DOI: 10.1073/pnas.1505317112] [Citation(s) in RCA: 111] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The type VI secretion system (T6SS) is a lethal weapon used by many bacteria to kill eukaryotic predators or prokaryotic competitors. Killing by the T6SS results from repetitive delivery of toxic effectors. Despite their importance in dictating bacterial fitness, systematic prediction of T6SS effectors remains challenging due to high effector diversity and the absence of a conserved signature sequence. Here, we report a class of T6SS effector chaperone (TEC) proteins that are required for effector delivery through binding to VgrG and effector proteins. The TEC proteins share a highly conserved domain (DUF4123) and are genetically encoded upstream of their cognate effector genes. Using the conserved TEC domain sequence, we identified a large family of TEC genes coupled to putative T6SS effectors in Gram-negative bacteria. We validated this approach by verifying a predicted effector TseC in Aeromonas hydrophila. We show that TseC is a T6SS-secreted antibacterial effector and that the downstream gene tsiC encodes the cognate immunity protein. Further, we demonstrate that TseC secretion requires its cognate TEC protein and an associated VgrG protein. Distinct from previous effector-dependent bioinformatic analyses, our approach using the conserved TEC domain will facilitate the discovery and functional characterization of new T6SS effectors in Gram-negative bacteria.
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62
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Sheibani-Tezerji R, Naveed M, Jehl MA, Sessitsch A, Rattei T, Mitter B. The genomes of closely related Pantoea ananatis maize seed endophytes having different effects on the host plant differ in secretion system genes and mobile genetic elements. Front Microbiol 2015; 6:440. [PMID: 26029184 PMCID: PMC4428218 DOI: 10.3389/fmicb.2015.00440] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2015] [Accepted: 04/23/2015] [Indexed: 11/13/2022] Open
Abstract
The seed as a habitat for microorganisms is as yet under-explored and has quite distinct characteristics as compared to other vegetative plant tissues. In this study, we investigated three closely related P. ananatis strains (named S6, S7, and S8), which were isolated from maize seeds of healthy plants. Plant inoculation experiments revealed that each of these strains exhibited a different phenotype ranging from weak pathogenic (S7), commensal (S8), to a beneficial, growth-promoting effect (S6) in maize. We performed a comparative genomics analysis in order to find genetic determinants responsible for the differences observed. Recent studies provided exciting insight into the genetic drivers of niche adaption and functional diversification of the genus Pantoea. However, we report here for the first time on the analysis of P. ananatis strains colonizing the same ecological niche but showing distinct interaction strategies with the host plant. Our comparative analysis revealed that genomes of these three strains are highly similar. However, genomic differences in genes encoding protein secretion systems and putative effectors, and transposase/integrases/phage related genes could be observed.
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Affiliation(s)
- Raheleh Sheibani-Tezerji
- Bioresources Unit, Health and Environment Department, AIT Austrian Institute of Technology GmbHTulln, Austria
- Division of Computational System Biology, Department of Microbiology and Ecosystem Science, University of ViennaVienna, Austria
| | - Muhammad Naveed
- Bioresources Unit, Health and Environment Department, AIT Austrian Institute of Technology GmbHTulln, Austria
| | - Marc-André Jehl
- Division of Computational System Biology, Department of Microbiology and Ecosystem Science, University of ViennaVienna, Austria
| | - Angela Sessitsch
- Bioresources Unit, Health and Environment Department, AIT Austrian Institute of Technology GmbHTulln, Austria
| | - Thomas Rattei
- Division of Computational System Biology, Department of Microbiology and Ecosystem Science, University of ViennaVienna, Austria
| | - Birgit Mitter
- Bioresources Unit, Health and Environment Department, AIT Austrian Institute of Technology GmbHTulln, Austria
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63
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Intraspecies Competition in Serratia marcescens Is Mediated by Type VI-Secreted Rhs Effectors and a Conserved Effector-Associated Accessory Protein. J Bacteriol 2015; 197:2350-60. [PMID: 25939831 PMCID: PMC4524185 DOI: 10.1128/jb.00199-15] [Citation(s) in RCA: 114] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2015] [Accepted: 04/24/2015] [Indexed: 12/27/2022] Open
Abstract
The 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 pathogen Serratia marcescens promotes 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, using S. 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 by S. marcescens EagR1, 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.
IMPORTANCE Infectious 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.
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64
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Li P, Kwok AHY, Jiang J, Ran T, Xu D, Wang W, Leung FC. Comparative genome analyses of Serratia marcescens FS14 reveals its high antagonistic potential. PLoS One 2015; 10:e0123061. [PMID: 25856195 PMCID: PMC4391916 DOI: 10.1371/journal.pone.0123061] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2014] [Accepted: 02/16/2015] [Indexed: 11/19/2022] Open
Abstract
S. marcescens FS14 was isolated from an Atractylodes macrocephala Koidz plant that was infected by Fusarium oxysporum and showed symptoms of root rot. With the completion of the genome sequence of FS14, the first comprehensive comparative-genomic analysis of the Serratia genus was performed. Pan-genome and COG analyses showed that the majority of the conserved core genes are involved in basic cellular functions, while genomic factors such as prophages contribute considerably to genome diversity. Additionally, a Type I restriction-modification system, a Type III secretion system and tellurium resistance genes are found in only some Serratia species. Comparative analysis further identified that S. marcescens FS14 possesses multiple mechanisms for antagonism against other microorganisms, including the production of prodigiosin, bacteriocins, and multi-antibiotic resistant determinants as well as chitinases. The presence of two evolutionarily distinct Type VI secretion systems (T6SSs) in FS14 may provide further competitive advantages for FS14 against other microbes. To our knowledge, this is the first report of comparative analysis on T6SSs in the genus, which identifies four types of T6SSs in Serratia spp.. Competition bioassays of FS14 against the vital plant pathogenic bacterium Ralstonia solanacearum and fungi Fusarium oxysporum and Sclerotinia sclerotiorum were performed to support our genomic analyses, in which FS14 demonstrated high antagonistic activities against both bacterial and fungal phytopathogens.
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Affiliation(s)
- Pengpeng Li
- Bioinformatics Center, Nanjing Agricultural University, Nanjing, China
| | - Amy H. Y. Kwok
- Bioinformatics Center, Nanjing Agricultural University, Nanjing, China
| | - Jingwei Jiang
- Bioinformatics Center, Nanjing Agricultural University, Nanjing, China
- School of Biological Sciences, University of Hong Kong, Hong Kong Special Administration Region, China
| | - Tingting Ran
- College of Life Sciences, Nanjing Agricultural University, Nanjing, China
| | - Dongqing Xu
- College of Life Sciences, Nanjing Agricultural University, Nanjing, China
| | - Weiwu Wang
- College of Life Sciences, Nanjing Agricultural University, Nanjing, China
| | - Frederick C. Leung
- Bioinformatics Center, Nanjing Agricultural University, Nanjing, China
- School of Biological Sciences, University of Hong Kong, Hong Kong Special Administration Region, China
- * E-mail:
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65
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Shyntum DY, Theron J, Venter SN, Moleleki LN, Toth IK, Coutinho TA. Pantoea ananatis Utilizes a Type VI Secretion System for Pathogenesis and Bacterial Competition. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2015; 28:420-431. [PMID: 25411959 DOI: 10.1094/mpmi-07-14-0219-r] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Type VI secretion systems (T6SSs) are a class of macromolecular machines that are recognized as an important virulence mechanism in several gram-negative bacteria. The genome of Pantoea ananatis LMG 2665(T), a pathogen of pineapple fruit and onion plants, carries two gene clusters whose predicted products have homology with T6SS-associated gene products from other bacteria. Nothing is known regarding the role of these T6SS-1 and T6SS-3 gene clusters in the biology of P. ananatis. Here, we present evidence that T6SS-1 plays an important role in the pathogenicity of P. ananatis LMG 2665(T) in onion plants, while a strain lacking T6SS-3 remains as pathogenic as the wild-type strain. We also investigated the role of the T6SS-1 system in bacterial competition, the results of which indicated that several bacteria compete less efficiently against wild-type LMG 2665(T) than a strain lacking T6SS-1. Additionally, we demonstrated that these phenotypes of strain LMG 2665(T) were reliant on the core T6SS products TssA and TssD (Hcp), thus indicating that the T6SS-1 gene cluster encodes a functioning T6SS. Collectively, our data provide the first evidence demonstrating that the T6SS-1 system is a virulence determinant of P. ananatis LMG 2665(T) and plays a role in bacterial competition.
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Affiliation(s)
- Divine Y Shyntum
- 1 Department of Microbiology and Plant Pathology, Faculty of Natural and Agricultural Sciences, and
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Hamilton JJ, Marlow VL, Owen RA, Costa MDAA, Guo M, Buchanan G, Chandra G, Trost M, Coulthurst SJ, Palmer T, Stanley-Wall NR, Sargent F. A holin and an endopeptidase are essential for chitinolytic protein secretion in Serratia marcescens. ACTA ACUST UNITED AC 2015; 207:615-26. [PMID: 25488919 PMCID: PMC4259817 DOI: 10.1083/jcb.201404127] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Pathogenic bacteria adapt to their environment and manipulate the biochemistry of hosts by secretion of effector molecules. Serratia marcescens is an opportunistic pathogen associated with healthcare-acquired infections and is a prolific secretor of proteins, including three chitinases (ChiA, ChiB, and ChiC) and a chitin binding protein (Cbp21). In this work, genetic, biochemical, and proteomic approaches identified genes that were required for secretion of all three chitinases and Cbp21. A genetic screen identified a holin-like protein (ChiW) and a putative l-alanyl-d-glutamate endopeptidase (ChiX), and subsequent biochemical analyses established that both were required for nonlytic secretion of the entire chitinolytic machinery, with chitinase secretion being blocked at a late stage in the mutants. In addition, live-cell imaging experiments demonstrated bimodal and coordinated expression of chiX and chiA and revealed that cells expressing chiA remained viable. It is proposed that ChiW and ChiX operate in tandem as components of a protein secretion system used by gram-negative bacteria.
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Affiliation(s)
- Jaeger J Hamilton
- Division of Molecular Microbiology and Medical Research Council Protein Phosphorylation Unit, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
| | - Victoria L Marlow
- Division of Molecular Microbiology and Medical Research Council Protein Phosphorylation Unit, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
| | - Richard A Owen
- Division of Molecular Microbiology and Medical Research Council Protein Phosphorylation Unit, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
| | - Marília de Assis Alcoforado Costa
- Division of Molecular Microbiology and Medical Research Council Protein Phosphorylation Unit, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
| | - Manman Guo
- Division of Molecular Microbiology and Medical Research Council Protein Phosphorylation Unit, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
| | - Grant Buchanan
- Division of Molecular Microbiology and Medical Research Council Protein Phosphorylation Unit, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
| | - Govind Chandra
- Department of Molecular Microbiology, John Innes Centre, Norwich NR4 7TJ, England, UK
| | - Matthias Trost
- Division of Molecular Microbiology and Medical Research Council Protein Phosphorylation Unit, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
| | - Sarah J Coulthurst
- Division of Molecular Microbiology and Medical Research Council Protein Phosphorylation Unit, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
| | - Tracy Palmer
- Division of Molecular Microbiology and Medical Research Council Protein Phosphorylation Unit, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
| | - Nicola R Stanley-Wall
- Division of Molecular Microbiology and Medical Research Council Protein Phosphorylation Unit, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
| | - Frank Sargent
- Division of Molecular Microbiology and Medical Research Council Protein Phosphorylation Unit, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, UK
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Against friend and foe: Type 6 effectors in plant-associated bacteria. J Microbiol 2015; 53:201-8. [DOI: 10.1007/s12275-015-5055-y] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2015] [Revised: 02/05/2015] [Accepted: 02/05/2015] [Indexed: 01/30/2023]
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Lu D, Zheng Y, Liao N, Wei L, Xu B, Liu X, Liu J. The structural basis of the Tle4–Tli4 complex reveals the self-protection mechanism of H2-T6SS inPseudomonas aeruginosa. ACTA ACUST UNITED AC 2014; 70:3233-43. [DOI: 10.1107/s1399004714023967] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2014] [Accepted: 10/30/2014] [Indexed: 01/02/2023]
Abstract
The type VI secretion system (T6SS) has recently been demonstrated to mediate interbacterial competition and to discriminate between self and nonself. T6SS+bacteria employ toxic effectors to inhibit rival cells and concurrently use effector cognate immunity proteins to protect their sibling cells. The effector and immunity pairs (E–I pairs) endow the bacteria with a great advantage in niche competition. Tle4–Tli4 (PA1510–PA1509) is a newly identified E–I pair that is controlled by H2-T6SS inPseudomonas aeruginosa. Tle4 exhibits phospholipase activity, which destroys the cell membrane of rival cells, and the periplasm-located Tli4 in donor cells eliminates this toxic effect of Tle4. In this paper, the structure of the Tle4–Tli4 complex is reported at 1.75 Å resolution. Tle4 consists of two domains: a conserved α/β-hydrolase domain and an unusual cap domain in which two lid regions (lid1 and lid2) display a closed conformation that buries the catalytic triad in a deep funnel. Tli4 also displays a two-domain structure, in which a large lobe and a small lobe form a crab claw-like conformation. Tli4 uses this crab claw to grasp the cap domain of Tle4, especially the lid2 region, which prevents the interfacial activation of Tle4 and thus causes enzymatic dysfunction of Tle4 in sister cells.
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69
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Durand E, Cambillau C, Cascales E, Journet L. VgrG, Tae, Tle, and beyond: the versatile arsenal of Type VI secretion effectors. Trends Microbiol 2014; 22:498-507. [DOI: 10.1016/j.tim.2014.06.004] [Citation(s) in RCA: 156] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2014] [Revised: 06/16/2014] [Accepted: 06/18/2014] [Indexed: 12/20/2022]
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Biochemical analysis of TssK, a core component of the bacterial Type VI secretion system, reveals distinct oligomeric states of TssK and identifies a TssK-TssFG subcomplex. Biochem J 2014; 461:291-304. [PMID: 24779861 PMCID: PMC4072051 DOI: 10.1042/bj20131426] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Gram-negative bacteria use the Type VI secretion system (T6SS) to inject toxic proteins into rival bacteria or eukaryotic cells. However, the mechanism of the T6SS is incompletely understood. In the present study, we investigated a conserved component of the T6SS, TssK, using the antibacterial T6SS of Serratia marcescens as a model system. TssK was confirmed to be essential for effector secretion by the T6SS. The native protein, although not an integral membrane protein, appeared to localize to the inner membrane, consistent with its presence within a membrane-anchored assembly. Recombinant TssK purified from S. marcescens was found to exist in several stable oligomeric forms, namely trimer, hexamer and higher-order species. Native-level purification of TssK identified TssF and TssG as interacting proteins. TssF and TssG, conserved T6SS components of unknown function, were required for T6SS activity, but not for correct localization of TssK. A complex containing TssK, TssF and TssG was subsequently purified in vitro, confirming that these three proteins form a new subcomplex within the T6SS. Our findings provide new insight into the T6SS assembly, allowing us to propose a model whereby TssK recruits TssFG into the membrane-associated T6SS complex and different oligomeric states of TssK may contribute to the dynamic mechanism of the system. Genetic and biochemical analysis of TssK, an essential component of the bacterial Type VI secretion system, revealed that it forms a new subcomplex with two other core components, TssF and TssG, and displays several oligomerization states in vitro.
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71
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Iguchi A, Nagaya Y, Pradel E, Ooka T, Ogura Y, Katsura K, Kurokawa K, Oshima K, Hattori M, Parkhill J, Sebaihia M, Coulthurst SJ, Gotoh N, Thomson NR, Ewbank JJ, Hayashi T. Genome evolution and plasticity of Serratia marcescens, an important multidrug-resistant nosocomial pathogen. Genome Biol Evol 2014; 6:2096-110. [PMID: 25070509 PMCID: PMC4231636 DOI: 10.1093/gbe/evu160] [Citation(s) in RCA: 127] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/21/2014] [Indexed: 01/24/2023] Open
Abstract
Serratia marcescens is an important nosocomial pathogen that can cause an array of infections, most notably of the urinary tract and bloodstream. Naturally, it is found in many environmental niches, and is capable of infecting plants and animals. The emergence and spread of multidrug-resistant strains producing extended-spectrum or metallo beta-lactamases now pose a threat to public health worldwide. Here we report the complete genome sequences of two carefully selected S. marcescens strains, a multidrug-resistant clinical isolate (strain SM39) and an insect isolate (strain Db11). Our comparative analyses reveal the core genome of S. marcescens and define the potential metabolic capacity, virulence, and multidrug resistance of this species. We show a remarkable intraspecies genetic diversity, both at the sequence level and with regards genome flexibility, which may reflect the diversity of niches inhabited by members of this species. A broader analysis with other Serratia species identifies a set of approximately 3,000 genes that characterize the genus. Within this apparent genetic diversity, we identified many genes implicated in the high virulence potential and antibiotic resistance of SM39, including the metallo beta-lactamase and multiple other drug resistance determinants carried on plasmid pSMC1. We further show that pSMC1 is most closely related to plasmids circulating in Pseudomonas species. Our data will provide a valuable basis for future studies on S. marcescens and new insights into the genetic mechanisms that underlie the emergence of pathogens highly resistant to multiple antimicrobial agents.
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Affiliation(s)
- Atsushi Iguchi
- Interdisciplinary Research Organization, University of Miyazaki, JapanPresent address: Department of Animal and Grassland Sciences, Faculty of Agriculture, University of Miyazaki, Japan
| | - Yutaka Nagaya
- Department of Microbiology and Infection Control Science, Kyoto Pharmaceutical University, JapanPresent address: Kashima ONC QC, Oncology DCU, Eisai Demand Chain Systems, Eisai Co., Ltd., Ibaraki, Japan
| | - Elizabeth Pradel
- Centre d'Immunologie de Marseille-Luminy, UM2 Aix-Marseille Université, Marseille, FranceINSERM, U1104, Marseille, FranceCNRS, UMR7280, Marseille, FrancePresent address: CIIL-Inserm U1019, Institut Pasteur de Lille, Lille, France
| | - Tadasuke Ooka
- Department of Infectious Diseases, Faculty of Medicine, University of Miyazaki, Japan
| | - Yoshitoshi Ogura
- Department of Infectious Diseases, Faculty of Medicine, University of Miyazaki, JapanDepartment of Genomics and Bioenvironmental Science, Frontier Science Research Center, University of Miyazaki, Japan
| | - Keisuke Katsura
- Department of Genomics and Bioenvironmental Science, Frontier Science Research Center, University of Miyazaki, Japan
| | - Ken Kurokawa
- Earth-Life Science Institute, Tokyo Institute of Technology, Kanagawa, Japan
| | - Kenshiro Oshima
- Graduate School of Frontier Sciences, University of Tokyo, Chiba, Japan
| | - Masahira Hattori
- Graduate School of Frontier Sciences, University of Tokyo, Chiba, Japan
| | - Julian Parkhill
- Pathogen Genomics, The Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Cambridge, United Kingdom
| | - Mohamed Sebaihia
- Pathogen Genomics, The Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Cambridge, United Kingdom
| | - Sarah J Coulthurst
- Division of Molecular Microbiology, College of Life Sciences, University of Dundee, United Kingdom
| | - Naomasa Gotoh
- Department of Microbiology and Infection Control Science, Kyoto Pharmaceutical University, Japan
| | - Nicholas R Thomson
- Pathogen Genomics, The Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Cambridge, United KingdomDepartment of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom
| | - Jonathan J Ewbank
- Centre d'Immunologie de Marseille-Luminy, UM2 Aix-Marseille Université, Marseille, FranceINSERM, U1104, Marseille, FranceCNRS, UMR7280, Marseille, France
| | - Tetsuya Hayashi
- Department of Infectious Diseases, Faculty of Medicine, University of Miyazaki, JapanDepartment of Genomics and Bioenvironmental Science, Frontier Science Research Center, University of Miyazaki, Japan
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Russell AB, Wexler AG, Harding BN, Whitney JC, Bohn AJ, Goo YA, Tran BQ, Barry NA, Zheng H, Peterson SB, Chou S, Gonen T, Goodlett DR, Goodman AL, Mougous JD. A type VI secretion-related pathway in Bacteroidetes mediates interbacterial antagonism. Cell Host Microbe 2014; 16:227-236. [PMID: 25070807 DOI: 10.1016/j.chom.2014.07.007] [Citation(s) in RCA: 241] [Impact Index Per Article: 24.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2014] [Revised: 07/04/2014] [Accepted: 07/09/2014] [Indexed: 12/12/2022]
Abstract
Bacteroidetes are a phylum of Gram-negative bacteria abundant in mammalian-associated polymicrobial communities, where they impact digestion, immunity, and resistance to infection. Despite the extensive competition at high cell density that occurs in these settings, cell contact-dependent mechanisms of interbacterial antagonism, such as the type VI secretion system (T6SS), have not been defined in this group of organisms. Herein we report the bioinformatic and functional characterization of a T6SS-like pathway in diverse Bacteroidetes. Using prominent human gut commensal and soil-associated species, we demonstrate that these systems localize dynamically within the cell, export antibacterial proteins, and target competitor bacteria. The Bacteroidetes system is a distinct pathway with marked differences in gene content and high evolutionary divergence from the canonical T6S pathway. Our findings offer a potential molecular explanation for the abundance of Bacteroidetes in polymicrobial environments, the observed stability of Bacteroidetes in healthy humans, and the barrier presented by the microbiota against pathogens.
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Affiliation(s)
- Alistair B Russell
- Department of Microbiology, University of Washington, Seattle, WA 98195, USA
| | - Aaron G Wexler
- Department of Microbial Pathogenesis and Microbial Diversity Institute, Yale University School of Medicine, New Haven, CT 06536, USA
| | - Brittany N Harding
- Department of Microbiology, University of Washington, Seattle, WA 98195, USA
| | - John C Whitney
- Department of Microbiology, University of Washington, Seattle, WA 98195, USA
| | - Alan J Bohn
- Department of Microbiology, University of Washington, Seattle, WA 98195, USA
| | - Young Ah Goo
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, MD 21201, USA
| | - Bao Q Tran
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, MD 21201, USA
| | - Natasha A Barry
- Department of Microbial Pathogenesis and Microbial Diversity Institute, Yale University School of Medicine, New Haven, CT 06536, USA
| | - Hongjin Zheng
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA 20147, USA
| | - S Brook Peterson
- Department of Microbiology, University of Washington, Seattle, WA 98195, USA
| | - Seemay Chou
- Department of Microbiology, University of Washington, Seattle, WA 98195, USA
| | - Tamir Gonen
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA 20147, USA
| | - David R Goodlett
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, MD 21201, USA
| | - Andrew L Goodman
- Department of Microbial Pathogenesis and Microbial Diversity Institute, Yale University School of Medicine, New Haven, CT 06536, USA.
| | - Joseph D Mougous
- Department of Microbiology, University of Washington, Seattle, WA 98195, USA.
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73
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Ma LS, Hachani A, Lin JS, Filloux A, Lai EM. Agrobacterium tumefaciens deploys a superfamily of type VI secretion DNase effectors as weapons for interbacterial competition in planta. Cell Host Microbe 2014; 16:94-104. [PMID: 24981331 PMCID: PMC4096383 DOI: 10.1016/j.chom.2014.06.002] [Citation(s) in RCA: 222] [Impact Index Per Article: 22.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2014] [Revised: 05/06/2014] [Accepted: 05/27/2014] [Indexed: 01/02/2023]
Abstract
The type VI secretion system (T6SS) is a widespread molecular weapon deployed by many Proteobacteria to target effectors/toxins into both eukaryotic and prokaryotic cells. We report that Agrobacterium tumefaciens, a soil bacterium that triggers tumorigenesis in plants, produces a family of type VI DNase effectors (Tde) that are distinct from previously known polymorphic toxins and nucleases. Tde exhibits an antibacterial DNase activity that relies on a conserved HxxD motif and can be counteracted by a cognate immunity protein, Tdi. In vitro, A. tumefaciens T6SS could kill Escherichia coli but triggered a lethal counterattack by Pseudomonas aeruginosa upon injection of the Tde toxins. However, in an in planta coinfection assay, A. tumefaciens used Tde effectors to attack both siblings cells and P. aeruginosa to ultimately gain a competitive advantage. Such acquired T6SS-dependent fitness in vivo and conservation of Tde-Tdi couples in bacteria highlights a widespread antibacterial weapon beneficial for niche colonization.
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Affiliation(s)
- Lay-Sun Ma
- Institute of Plant and Microbial Biology, Academia Sinica, Taipei 11529, Taiwan; MRC Centre for Molecular Bacteriology and Infection, Department of Life Sciences, Imperial College London, London SW7 2AZ, UK
| | - Abderrahman Hachani
- MRC Centre for Molecular Bacteriology and Infection, Department of Life Sciences, Imperial College London, London SW7 2AZ, UK
| | - Jer-Sheng Lin
- Institute of Plant and Microbial Biology, Academia Sinica, Taipei 11529, Taiwan
| | - Alain Filloux
- MRC Centre for Molecular Bacteriology and Infection, Department of Life Sciences, Imperial College London, London SW7 2AZ, UK.
| | - Erh-Min Lai
- Institute of Plant and Microbial Biology, Academia Sinica, Taipei 11529, Taiwan.
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74
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Hachani A, Allsopp LP, Oduko Y, Filloux A. The VgrG proteins are "à la carte" delivery systems for bacterial type VI effectors. J Biol Chem 2014; 289:17872-84. [PMID: 24794869 PMCID: PMC4067218 DOI: 10.1074/jbc.m114.563429] [Citation(s) in RCA: 140] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022] Open
Abstract
The bacterial type VI secretion system (T6SS) is a supra-molecular complex akin to bacteriophage tails, with VgrG proteins acting as a puncturing device. The Pseudomonas aeruginosa H1-T6SS has been extensively characterized. It is involved in bacterial killing and in the delivery of three toxins, Tse1–3. Here, we demonstrate the independent contribution of the three H1-T6SS co-regulated vgrG genes, vgrG1abc, to bacterial killing. A putative toxin is encoded in the vicinity of each vgrG gene, supporting the concept of specific VgrG/toxin couples. In this respect, VgrG1c is involved in the delivery of an Rhs protein, RhsP1. The RhsP1 C terminus carries a toxic activity, from which the producing bacterium is protected by a cognate immunity. Similarly, VgrG1a-dependent toxicity is associated with the PA0093 gene encoding a two-domain protein with a putative toxin domain (Toxin_61) at the C terminus. Finally, VgrG1b-dependent killing is detectable upon complementation of a triple vgrG1abc mutant. The VgrG1b-dependent killing is mediated by PA0099, which presents the characteristics of the superfamily nuclease 2 toxin members. Overall, these data develop the concept that VgrGs are indispensable components for the specific delivery of effectors. Several additional vgrG genes are encoded on the P. aeruginosa genome and are not linked genetically to other T6SS genes. A closer inspection of these clusters reveals that they also encode putative toxins. Overall, these associations further support the notion of an original form of secretion system, in which VgrG acts as the carrier.
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Affiliation(s)
- Abderrahman Hachani
- From the MRC Centre for Molecular Bacteriology and Infection, Department of Life Sciences, Imperial College London, London SW7 2AZ, United Kingdom
| | - Luke P Allsopp
- From the MRC Centre for Molecular Bacteriology and Infection, Department of Life Sciences, Imperial College London, London SW7 2AZ, United Kingdom
| | - Yewande Oduko
- From the MRC Centre for Molecular Bacteriology and Infection, Department of Life Sciences, Imperial College London, London SW7 2AZ, United Kingdom
| | - Alain Filloux
- From the MRC Centre for Molecular Bacteriology and Infection, Department of Life Sciences, Imperial College London, London SW7 2AZ, United Kingdom
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75
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Yang X, Xu M, Wang Y, Xia P, Wang S, Ye B, Tong L, Jiang T, Fan Z. Molecular mechanism for self-protection against the type VI secretion system inVibrio cholerae. ACTA ACUST UNITED AC 2014; 70:1094-103. [DOI: 10.1107/s1399004714001242] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2013] [Accepted: 01/17/2014] [Indexed: 01/21/2023]
Abstract
VgrG proteins form the spike of the type VI secretion system (T6SS) syringe-like complex. VgrG3 ofVibrio choleraedegrades the peptidoglycan cell wall of rival bacteriaviaits C-terminal region (VgrG3C) through its muramidase activity. VgrG3C consists of a peptidoglycan-binding domain (VgrG3CPGB) and a putative catalytic domain (VgrG3CCD), and its activity can be inhibited by its immunity protein partner TsiV3. Here, the crystal structure ofV. choleraeVgrG3CCDin complex with TsiV3 is presented at 2.3 Å resolution. VgrG3CCDadopts a chitosanase fold. A dimer of TsiV3 is bound in the deep active-site groove of VgrG3CCD, occluding substrate binding and distorting the conformation of the catalytic dyad. Gln91 and Arg92 of TsiV3 are located in the centre of the interface and are important for recognition of VgrG3C. Mutation of these residues destabilized the complex and abolished the inhibitory activity of TsiV3 against VgrG3C toxicity in cells. Disruption of TsiV3 dimerization also weakened the complex and impaired the inhibitory activity. These structural, biochemical and functional data define the molecular mechanism underlying the self-protection ofV. choleraeand expand the understanding of the role of T6SS in bacterial competition.
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76
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Lin JS, Wu HH, Hsu PH, Ma LS, Pang YY, Tsai MD, Lai EM. Fha interaction with phosphothreonine of TssL activates type VI secretion in Agrobacterium tumefaciens. PLoS Pathog 2014; 10:e1003991. [PMID: 24626341 PMCID: PMC3953482 DOI: 10.1371/journal.ppat.1003991] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2013] [Accepted: 01/27/2014] [Indexed: 11/26/2022] Open
Abstract
The type VI secretion system (T6SS) is a widespread protein secretion system found in many Gram-negative bacteria. T6SSs are highly regulated by various regulatory systems at multiple levels, including post-translational regulation via threonine (Thr) phosphorylation. The Ser/Thr protein kinase PpkA is responsible for this Thr phosphorylation regulation, and the forkhead-associated (FHA) domain-containing Fha-family protein is the sole T6SS phosphorylation substrate identified to date. Here we discovered that TssL, the T6SS inner-membrane core component, is phosphorylated and the phosphorylated TssL (p-TssL) activates type VI subassembly and secretion in a plant pathogenic bacterium, Agrobacterium tumefaciens. Combining genetic and biochemical approaches, we demonstrate that TssL is phosphorylated at Thr 14 in a PpkA-dependent manner. Further analysis revealed that the PpkA kinase activity is responsible for the Thr 14 phosphorylation, which is critical for the secretion of the T6SS hallmark protein Hcp and the putative toxin effector Atu4347. TssL phosphorylation is not required for the formation of the TssM-TssL inner-membrane complex but is critical for TssM conformational change and binding to Hcp and Atu4347. Importantly, Fha specifically interacts with phosphothreonine of TssL via its pThr-binding motif in vivo and in vitro and this interaction is crucial for TssL interaction with Hcp and Atu4347 and activation of type VI secretion. In contrast, pThr-binding ability of Fha is dispensable for TssM structural transition. In conclusion, we discover a novel Thr phosphorylation event, in which PpkA phosphorylates TssL to activate type VI secretion via its direct binding to Fha in A. tumefaciens. A model depicting an ordered TssL phosphorylation-induced T6SS assembly pathway is proposed. The bacterial type VI secretion system (T6SS) resembles a contractile phage tail structure and functions to deliver effectors to eukaryotic or prokaryotic target cells for the survival of many pathogenic bacteria. T6SS is highly regulated by various regulatory systems at multiple levels in response to environmental cues. Post-translational regulation via threonine (Thr) phosphorylation is an emerging theme in regulating prokaryotic signaling, including T6SS; the knowledge is mainly contributed by studies of Hcp secretion island 1-encoded T6SS (H1-T6SS) of Pseudomonas aeruginosa. Here, we discover a new phosphorylated target, a T6SS core-component TssL, and demonstrate that this Thr phosphorylation event post-translationally regulates type VI secretion in a plant pathogenic bacterium, Agrobacterium tumefaciens. We provide the first demonstration that the specific binding of Fha, a forkhead-associated domain-containing protein, to the phosphorylated target is required to stimulate type VI secretion. Genetic and biochemical data strongly suggest an ordered TssL-phosphorylation–dependent assembly and secretion pathway.
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Affiliation(s)
- Jer-Sheng Lin
- Institute of Plant and Microbial Biology, Academia Sinica, Taipei, Taiwan
| | - Hsin-Hui Wu
- Institute of Biological Chemistry, Academia Sinica, Taipei, Taiwan; Structural Biology Program, National Tsing Hua University, Hsinchu, Taiwan; Institute of Bioinformatics and Structural Biology, National Tsing Hua University, Hsinchu, Taiwan
| | - Pang-Hung Hsu
- Institute of Biological Chemistry, Academia Sinica, Taipei, Taiwan; Genomics Research Center, Academia Sinica, Taipei, Taiwan; Department of Life Science, Institute of Bioscience and Biotechnology, National Taiwan Ocean University, Keelung, Taiwan
| | - Lay-Sun Ma
- Institute of Plant and Microbial Biology, Academia Sinica, Taipei, Taiwan
| | - Yin-Yuin Pang
- Institute of Plant and Microbial Biology, Academia Sinica, Taipei, Taiwan
| | - Ming-Daw Tsai
- Institute of Biological Chemistry, Academia Sinica, Taipei, Taiwan; Structural Biology Program, National Tsing Hua University, Hsinchu, Taiwan; Genomics Research Center, Academia Sinica, Taipei, Taiwan; Institute of Biochemical Sciences, National Taiwan University, Taipei, Taiwan
| | - Erh-Min Lai
- Institute of Plant and Microbial Biology, Academia Sinica, Taipei, Taiwan
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Shyntum DY, Venter SN, Moleleki LN, Toth I, Coutinho TA. Comparative genomics of type VI secretion systems in strains of Pantoea ananatis from different environments. BMC Genomics 2014; 15:163. [PMID: 24571088 PMCID: PMC3942780 DOI: 10.1186/1471-2164-15-163] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2013] [Accepted: 02/18/2014] [Indexed: 11/25/2022] Open
Abstract
BACKGROUND The Type VI secretion system (T6SS) has been identified in several different bacteria, including the plant pathogenPantoea ananatis. Previous in silico analyses described three different T6SS loci present in the pathogenic strain of P. ananatis LMG 20103. This initial investigation has been extended to include an additional seven sequenced strains of P. ananatis together with 39 strains from different ecological niches. Comparative and phylogenetic analyses were used to investigate the distribution, evolution, intra-strain variability and operon structure of the T6SS in the sequenced strains. RESULTS Three different T6SS loci were identified in P. ananatis strain LMG 20103 and designated PA T6SS 1-3. PA T6SS-1 was present in all sequenced strains of P. ananatis and in all 39 additional strains examined in this study. In addition, PA T6SS-1 included all 13 core T6SS genes required for synthesis of a functional T6SS. The plasmid-borne PA T6SS-2 also included all 13 core T6SS genes but was restricted to only 33% (15/46) of the strains examined. In addition, PA T6SS-2 was restricted to strains of P. ananatis isolated from symptomatic plant material. This finding raises the possibility of an association between PA T6SS-2 and either pathogenicity or host specificity. The third cluster PA T6SS-3 was present in all strains analyzed in this study but lacked 11 of the 13 core T6SS genes suggesting it may not encoded a functional T6SS. Inter-strain variability was also associated with hcp and vgrG islands, which are associated with the T6SS and encode a variable number of proteins usually of unknown function. These proteins may play a role in the fitness of different strains in a variety of ecological niches or as candidate T6SS effectors. Phylogenetic analysis indicated that PA T6SS-1 and PA T6SS-2 are evolutionarily distinct. CONCLUSION Our analysis indicates that the three T6SSs of P. ananatis appear to have been independently acquired and may play different roles relating to pathogenicity, host range determination and/or niche adaptation. Future work will be directed toward understanding the roles that these T6SSs play in the biology of P. ananatis.
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Affiliation(s)
- Divine Yufetar Shyntum
- Department of Microbiology and Plant Pathology, Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, Pretoria, South Africa
| | - Stephanus Nicolaas Venter
- Department of Microbiology and Plant Pathology, Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, Pretoria, South Africa
| | - Lucy Novungayo Moleleki
- Department of Microbiology and Plant Pathology, Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, Pretoria, South Africa
| | - Ian Toth
- Department of Microbiology and Plant Pathology, Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, Pretoria, South Africa
- James Hutton Research Institute, Invergowrie, Dundee DD2 5DA, Scotland, UK
| | - Teresa Ann Coutinho
- Department of Microbiology and Plant Pathology, Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, Pretoria, South Africa
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Decoin V, Barbey C, Bergeau D, Latour X, Feuilloley MGJ, Orange N, Merieau A. A type VI secretion system is involved in Pseudomonas fluorescens bacterial competition. PLoS One 2014; 9:e89411. [PMID: 24551247 PMCID: PMC3925238 DOI: 10.1371/journal.pone.0089411] [Citation(s) in RCA: 63] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2013] [Accepted: 01/21/2014] [Indexed: 11/23/2022] Open
Abstract
Protein secretion systems are crucial mediators of bacterial interactions with other organisms. Among them, the type VI secretion system (T6SS) is widespread in Gram-negative bacteria and appears to inject toxins into competitor bacteria and/or eukaryotic cells. Major human pathogens, such as Vibrio cholerae, Burkholderia and Pseudomonas aeruginosa, express T6SSs. Bacteria prevent self-intoxication by their own T6SS toxins by producing immunity proteins, which interact with the cognate toxins. We describe here an environmental P. fluorescens strain, MFE01, displaying an uncommon oversecretion of Hcp (hemolysin-coregulated protein) and VgrG (valine-glycine repeat protein G) into the culture medium. These proteins are characteristic components of a functional T6SS. The aim of this study was to attribute a role to this energy-consuming overexpression of the T6SS. The genome of MFE01 contains at least two hcp genes (hcp1 and hcp2), suggesting that there may be two putative T6SS clusters. Phenotypic studies have shown that MFE01 is avirulent against various eukaryotic cell models (amebas, plant or animal cell models), but has antibacterial activity against a wide range of competitor bacteria, including rhizobacteria and clinical bacteria. Depending on the prey cell, mutagenesis of the hcp2 gene in MFE01 abolishes or reduces this antibacterial killing activity. Moreover, the introduction of T6SS immunity proteins from S. marcescens, which is not killed by MFE01, protects E. coli against MFE01 killing. These findings suggest that the protein encoded by hcp2 is involved in the killing activity of MFE01 mediated by effectors of the T6SS targeting the peptidoglycan of Gram-negative bacteria. Our results indicate that MFE01 can protect potato tubers against Pectobacterium atrosepticum, which causes tuber soft rot. Pseudomonas fluorescens is often described as a major PGPR (plant growth-promoting rhizobacterium), and our results suggest that there may be a connection between the T6SS and the PGPR properties of this bacterium.
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Affiliation(s)
- Victorien Decoin
- LMSM, Laboratoire de Microbiologie Signaux et Microenvironnement, Normandie Université, EA 4312, Université de Rouen, IUT d'Evreux, Evreux, France
| | - Corinne Barbey
- LMSM, Laboratoire de Microbiologie Signaux et Microenvironnement, Normandie Université, EA 4312, Université de Rouen, IUT d'Evreux, Evreux, France
| | - Dorian Bergeau
- LMSM, Laboratoire de Microbiologie Signaux et Microenvironnement, Normandie Université, EA 4312, Université de Rouen, IUT d'Evreux, Evreux, France
| | - Xavier Latour
- LMSM, Laboratoire de Microbiologie Signaux et Microenvironnement, Normandie Université, EA 4312, Université de Rouen, IUT d'Evreux, Evreux, France
| | - Marc G J Feuilloley
- LMSM, Laboratoire de Microbiologie Signaux et Microenvironnement, Normandie Université, EA 4312, Université de Rouen, IUT d'Evreux, Evreux, France
| | - Nicole Orange
- LMSM, Laboratoire de Microbiologie Signaux et Microenvironnement, Normandie Université, EA 4312, Université de Rouen, IUT d'Evreux, Evreux, France
| | - Annabelle Merieau
- LMSM, Laboratoire de Microbiologie Signaux et Microenvironnement, Normandie Université, EA 4312, Université de Rouen, IUT d'Evreux, Evreux, France
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79
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Russell AB, Peterson SB, Mougous JD. Type VI secretion system effectors: poisons with a purpose. Nat Rev Microbiol 2014; 12:137-48. [PMID: 24384601 DOI: 10.1038/nrmicro3185] [Citation(s) in RCA: 501] [Impact Index Per Article: 50.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The type VI secretion system (T6SS) mediates interactions between a broad range of Gram-negative bacterial species. Recent studies have led to a substantial increase in the number of characterized T6SS effector proteins and a more complete and nuanced view of the adaptive importance of the system. Although the T6SS is most often implicated in antagonism, in this Review, we consider the case for its involvement in both antagonistic and non-antagonistic behaviours. Clarifying the roles that type VI secretion has in microbial communities will contribute to broader efforts to understand the importance of microbial interactions in maintaining human and environmental health, and will inform efforts to manipulate these interactions for therapeutic or environmental benefit.
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Affiliation(s)
- Alistair B Russell
- Department of Microbiology, University of Washington, Seattle, Washington 98195, USA
| | - S Brook Peterson
- Department of Microbiology, University of Washington, Seattle, Washington 98195, USA
| | - Joseph D Mougous
- Department of Microbiology, University of Washington, Seattle, Washington 98195, USA
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80
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Abstract
The bacterial type VI secretion system (T6SS) is an organelle that is structurally and mechanistically analogous to an intracellular membrane-attached contractile phage tail. Recent studies determined that a rapid conformational change in the structure of a sheath protein complex propels T6SS spike and tube components along with antibacterial and antieukaryotic effectors out of predatory T6SS(+) cells and into prey cells. The contracted organelle is then recycled in an ATP-dependent process. T6SS is regulated at transcriptional and posttranslational levels, the latter involving detection of membrane perturbation in some species. In addition to directly targeting eukaryotic cells, the T6SS can also target other bacteria coinfecting a mammalian host, highlighting the importance of the T6SS not only for bacterial survival in environmental ecosystems, but also in the context of infection and disease. This review highlights these and other advances in our understanding of the structure, mechanical function, assembly, and regulation of the T6SS.
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Affiliation(s)
- Brian T Ho
- Department of Microbiology and Immunobiology, Harvard Medical School, 77 Avenue Louis Pasteur, Boston, MA 02115, USA
| | - Tao G Dong
- Department of Microbiology and Immunobiology, Harvard Medical School, 77 Avenue Louis Pasteur, Boston, MA 02115, USA
| | - John J Mekalanos
- Department of Microbiology and Immunobiology, Harvard Medical School, 77 Avenue Louis Pasteur, Boston, MA 02115, USA.
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81
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Benz J, Meinhart A. Antibacterial effector/immunity systems: it's just the tip of the iceberg. Curr Opin Microbiol 2013; 17:1-10. [PMID: 24581686 DOI: 10.1016/j.mib.2013.11.002] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2013] [Revised: 10/31/2013] [Accepted: 11/09/2013] [Indexed: 01/22/2023]
Abstract
Bacteria do not live anchoretic; rather they are constantly in touch with their eukaryotic hosts and with other bacteria sharing their habitat. Therefore, bacteria have evolved sophisticated proteinaceous weapons. To harm other bacteria, they produce antibacterial effector proteins, which they either release into the environment or export via direct intercellular contact. Contact-dependent killing is mediated by two specialized secretion systems, the type V and VI secretion system, whereas contact-independent processes hijack other transport mechanisms. Regardless of the transport system, cells co-express immunity proteins to protect themselves from suicide and fratricide. In general, effector protein activities and secretion mechanisms differ between Gram-positive and Gram-negative bacteria and evidence is emerging that different effector/immunity systems act synergistically and thus extend the bacterial armory.
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Affiliation(s)
- Juliane Benz
- Department of Biomolecular Mechanisms, Max-Planck Institute for Medical Research, Jahnstrasse 29, 69120 Heidelberg, Germany
| | - Anton Meinhart
- Department of Biomolecular Mechanisms, Max-Planck Institute for Medical Research, Jahnstrasse 29, 69120 Heidelberg, Germany.
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82
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Srikannathasan V, English G, Bui NK, Trunk K, O’Rourke PEF, Rao VA, Vollmer W, Coulthurst SJ, Hunter WN. Structural basis for type VI secreted peptidoglycan DL-endopeptidase function, specificity and neutralization in Serratia marcescens. ACTA CRYSTALLOGRAPHICA. SECTION D, BIOLOGICAL CRYSTALLOGRAPHY 2013; 69:2468-82. [PMID: 24311588 PMCID: PMC3852654 DOI: 10.1107/s0907444913022725] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/16/2013] [Accepted: 08/13/2013] [Indexed: 11/10/2022]
Abstract
Some Gram-negative bacteria target their competitors by exploiting the type VI secretion system to extrude toxic effector proteins. To prevent self-harm, these bacteria also produce highly specific immunity proteins that neutralize these antagonistic effectors. Here, the peptidoglycan endopeptidase specificity of two type VI secretion-system-associated effectors from Serratia marcescens is characterized. These small secreted proteins, Ssp1 and Ssp2, cleave between γ-D-glutamic acid and L-meso-diaminopimelic acid with different specificities. Ssp2 degrades the acceptor part of cross-linked tetratetrapeptides. Ssp1 displays greater promiscuity and cleaves monomeric tripeptides, tetrapeptides and pentapeptides and dimeric tetratetra and tetrapenta muropeptides on both the acceptor and donor strands. Functional assays confirm the identity of a catalytic cysteine in these endopeptidases and crystal structures provide information on the structure-activity relationships of Ssp1 and, by comparison, of related effectors. Functional assays also reveal that neutralization of these effectors by their cognate immunity proteins, which are called resistance-associated proteins (Raps), contributes an essential role to cell fitness. The structures of two immunity proteins, Rap1a and Rap2a, responsible for the neutralization of Ssp1 and Ssp2-like endopeptidases, respectively, revealed two distinct folds, with that of Rap1a not having previously been observed. The structure of the Ssp1-Rap1a complex revealed a tightly bound heteromeric assembly with two effector molecules flanking a Rap1a dimer. A highly effective steric block of the Ssp1 active site forms the basis of effector neutralization. Comparisons with Ssp2-Rap2a orthologues suggest that the specificity of these immunity proteins for neutralizing effectors is fold-dependent and that in cases where the fold is conserved sequence differences contribute to the specificity of effector-immunity protein interactions.
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Affiliation(s)
- Velupillai Srikannathasan
- Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland
| | - Grant English
- Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland
| | - Nhat Khai Bui
- Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne NE2 4HH, England
| | - Katharina Trunk
- Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland
| | - Patrick E. F. O’Rourke
- Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland
| | - Vincenzo A. Rao
- Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland
| | - Waldemar Vollmer
- Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne NE2 4HH, England
| | - Sarah J. Coulthurst
- Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland
| | - William N. Hunter
- Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland
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83
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Zhang XY, Brunet YR, Logger L, Douzi B, Cambillau C, Journet L, Cascales E. Dissection of the TssB-TssC interface during type VI secretion sheath complex formation. PLoS One 2013; 8:e81074. [PMID: 24282569 PMCID: PMC3840085 DOI: 10.1371/journal.pone.0081074] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2013] [Accepted: 10/09/2013] [Indexed: 11/18/2022] Open
Abstract
The Type VI secretion system (T6SS) is a versatile machine that delivers toxins into either eukaryotic or bacterial cells. At a molecular level, the T6SS is composed of a membrane complex that anchors a long cytoplasmic tubular structure to the cell envelope. This structure is thought to resemble the tail of contractile bacteriophages. It is composed of the Hcp protein that assembles into hexameric rings stacked onto each other to form a tube similar to the phage tail tube. This tube is proposed to be wrapped by a structure called the sheath, composed of two proteins, TssB and TssC. It has been shown using fluorescence microscopy that the TssB and TssC proteins assemble into a tubular structure that cycles between long and short conformations suggesting that, similarly to the bacteriophage sheath, the T6SS sheath undergoes elongation and contraction events. The TssB and TssC proteins have been shown to interact and a specific α-helix of TssB is required for this interaction. Here, we confirm that the TssB and TssC proteins interact in enteroaggregative E. coli. We further show that this interaction requires the N-terminal region of TssC and the conserved α-helix of TssB. Using site-directed mutagenesis coupled to phenotypic analyses, we demonstrate that an hydrophobic motif located in the N-terminal region of this helix is required for interaction with TssC, sheath assembly and T6SS function.
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Affiliation(s)
- Xiang Y. Zhang
- Laboratoire d′Ingénierie des Systèmes Macromoléculaires (LISM, UMR 7255), Institut de Microbiologie de la Méditerranée (IMM), Centre National de la Recherche Scientifique (CNRS), Aix-Marseille Université, Marseille, France
| | - Yannick R. Brunet
- Laboratoire d′Ingénierie des Systèmes Macromoléculaires (LISM, UMR 7255), Institut de Microbiologie de la Méditerranée (IMM), Centre National de la Recherche Scientifique (CNRS), Aix-Marseille Université, Marseille, France
| | - Laureen Logger
- Laboratoire d′Ingénierie des Systèmes Macromoléculaires (LISM, UMR 7255), Institut de Microbiologie de la Méditerranée (IMM), Centre National de la Recherche Scientifique (CNRS), Aix-Marseille Université, Marseille, France
| | - Badreddine Douzi
- Architecture et Fonction des Macromolécules Biologiques (AFMB, UMR 6098), Centre National de la Recherche Scientifique (CNRS), Aix-Marseille Université, Marseille, France
| | - Christian Cambillau
- Architecture et Fonction des Macromolécules Biologiques (AFMB, UMR 6098), Centre National de la Recherche Scientifique (CNRS), Aix-Marseille Université, Marseille, France
| | - Laure Journet
- Laboratoire d′Ingénierie des Systèmes Macromoléculaires (LISM, UMR 7255), Institut de Microbiologie de la Méditerranée (IMM), Centre National de la Recherche Scientifique (CNRS), Aix-Marseille Université, Marseille, France
| | - Eric Cascales
- Laboratoire d′Ingénierie des Systèmes Macromoléculaires (LISM, UMR 7255), Institut de Microbiologie de la Méditerranée (IMM), Centre National de la Recherche Scientifique (CNRS), Aix-Marseille Université, Marseille, France
- * E-mail: *
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84
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Burkholderia mallei and Burkholderia pseudomallei cluster 1 type VI secretion system gene expression is negatively regulated by iron and zinc. PLoS One 2013; 8:e76767. [PMID: 24146925 PMCID: PMC3795662 DOI: 10.1371/journal.pone.0076767] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2013] [Accepted: 09/03/2013] [Indexed: 02/02/2023] Open
Abstract
Burkholderia mallei is a facultative intracellular pathogen that causes glanders in humans and animals. Previous studies have demonstrated that the cluster 1 type VI secretion system (T6SS-1) expressed by this organism is essential for virulence in hamsters and is positively regulated by the VirAG two-component system. Recently, we have shown that T6SS-1 gene expression is up-regulated following internalization of this pathogen into phagocytic cells and that this system promotes multinucleated giant cell formation in infected tissue culture monolayers. In the present study, we further investigated the complex regulation of this important virulence factor. To assess T6SS-1 expression, B. mallei strains were cultured in various media conditions and Hcp1 production was analyzed by Western immunoblotting. Transcript levels of several VirAG-regulated genes (bimA, tssA, hcp1 and tssM) were also determined using quantitative real time PCR. Consistent with previous observations, T6SS-1 was not expressed during growth of B. mallei in rich media. Curiously, growth of the organism in minimal media (M9G) or minimal media plus casamino acids (M9CG) facilitated robust expression of T6SS-1 genes whereas growth in minimal media plus tryptone (M9TG) did not. Investigation of this phenomenon confirmed a regulatory role for VirAG in this process. Additionally, T6SS-1 gene expression was significantly down-regulated by the addition of iron and zinc to M9CG. Other genes under the control of VirAG did not appear to be as tightly regulated by these divalent metals. Similar results were observed for B. pseudomallei, but not for B. thailandensis. Collectively, our findings indicate that in addition to being positively regulated by VirAG, B. mallei and B. pseudomallei T6SS-1 gene expression is negatively regulated by iron and zinc.
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85
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Institut Pasteur Minisymposium on Bacterial Membranes 2013. Res Microbiol 2013. [DOI: 10.1016/j.resmic.2013.06.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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86
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Petersen LM, Tisa LS. Friend or foe? A review of the mechanisms that driveSerratiatowards diverse lifestyles. Can J Microbiol 2013; 59:627-40. [DOI: 10.1139/cjm-2013-0343] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Found widespread around the globe, Serratia are Gram-negative bacteria capable of thriving in a diverse number of environments that include water, soil, and the digestive tracts of various animals. Known for their ability to produce a myriad of extracellular enzymes, these bacteria also produce various secondary metabolites that directly contribute to their survival. While the effects Serratia species have on other organisms range from parasitic to symbiotic, what these bacteria have in common is their ability to resist attack, respond appropriately to environmental conditions, and outcompete other microorganisms when colonizing their respective niche. This review highlights the mechanisms utilized by Serratia species that drive their ubiquitous nature, with emphasis on the latest findings. Also discussed is how secreted compounds drive these bacteria towards pathogenic, mutualistic, and antagonistic associations.
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Affiliation(s)
- Lauren M. Petersen
- Department of Molecular, Cellular, and Biomedical Sciences, University of New Hampshire, 46 College Road, Durham, NH 03824-2617, USA
| | - Louis S. Tisa
- Department of Molecular, Cellular, and Biomedical Sciences, University of New Hampshire, 46 College Road, Durham, NH 03824-2617, USA
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87
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Robert-Genthon M, Casabona MG, Neves D, Couté Y, Cicéron F, Elsen S, Dessen A, Attrée I. Unique features of a Pseudomonas aeruginosa α2-macroglobulin homolog. mBio 2013; 4:e00309-13. [PMID: 23919994 PMCID: PMC3735191 DOI: 10.1128/mbio.00309-13] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2013] [Accepted: 07/11/2013] [Indexed: 12/20/2022] Open
Abstract
UNLABELLED Human pathogens frequently use protein mimicry to manipulate host cells in order to promote their survival. Here we show that the opportunistic pathogen Pseudomonas aeruginosa synthesizes a structural homolog of the human α2-macroglobulin, a large-spectrum protease inhibitor and important player of innate immunity. Small-angle X-ray scattering analysis demonstrated that the fold of P. aeruginosa MagD (PA4489) is similar to that of the human macroglobulin and undergoes a conformational modification upon binding of human neutrophil elastase. MagD synthesis is under the control of a general virulence regulatory pathway including the inner membrane sensor RetS and the RNA-binding protein RsmA, and MagD undergoes cleavage from a 165-kDa to a 100-kDa form in all clinical isolates tested. Fractionation and immunoprecipitation experiments showed that MagD is translocated to the bacterial periplasm and resides within the inner membrane in a complex with three other molecular partners, MagA, MagB, and MagF, all of them encoded by the same six-gene genetic element. Inactivation of the whole 10-kb operon on the PAO1 genome resulted in mislocalization of uncleaved, in trans-provided MagD as well as its rapid degradation. Thus, pathogenic bacteria have acquired a homolog of human macroglobulin that plays roles in host-pathogen interactions potentially through recognition of host proteases and/or antimicrobial peptides; it is thus essential for bacterial defense. IMPORTANCE The pathogenesis of Pseudomonas aeruginosa is multifactorial and relies on surface-associated and secreted proteins with different toxic activities. Here we show that the bacterium synthesizes a 160-kDa structural homolog of the human large-spectrum protease inhibitor α2-macroglobulin. The bacterial protein is localized in the periplasm and is associated with the inner membrane through the formation of a multimolecular complex. Its synthesis is coregulated at the posttranscriptional level with other virulence determinants, suggesting that it has a role in bacterial pathogenicity and/or in defense against the host immune system. Thus, this new P. aeruginosa macromolecular complex may represent a future target for antibacterial developments.
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Affiliation(s)
| | | | - David Neves
- Brazilian National Laboratory for Biosciences (LNBio), CNPEM, Campinas, São Paulo, Brazil
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88
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Whitney JC, Chou S, Russell AB, Biboy J, Gardiner TE, Ferrin MA, Brittnacher M, Vollmer W, Mougous JD. Identification, structure, and function of a novel type VI secretion peptidoglycan glycoside hydrolase effector-immunity pair. J Biol Chem 2013; 288:26616-24. [PMID: 23878199 DOI: 10.1074/jbc.m113.488320] [Citation(s) in RCA: 90] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Bacteria employ type VI secretion systems (T6SSs) to facilitate interactions with prokaryotic and eukaryotic cells. Despite the widespread identification of T6SSs among Gram-negative bacteria, the number of experimentally validated substrate effector proteins mediating these interactions remains small. Here, employing an informatics approach, we define novel families of T6S peptidoglycan glycoside hydrolase effectors. Consistent with the known intercellular self-intoxication exhibited by the T6S pathway, we observe that each effector gene is located adjacent to a hypothetical open reading frame encoding a putative periplasmically localized immunity determinant. To validate our sequence-based approach, we functionally investigate a representative family member from the soil-dwelling bacterium Pseudomonas protegens. We demonstrate that this protein is secreted in a T6SS-dependent manner and that it confers a fitness advantage in growth competition assays with Pseudomonas putida. In addition, we determined the 1.4 Å x-ray crystal structure of this effector in complex with its cognate immunity protein. The structure reveals the effector shares highest overall structural similarity to a glycoside hydrolase family associated with peptidoglycan N-acetylglucosaminidase activity, suggesting that T6S peptidoglycan glycoside hydrolase effector families may comprise significant enzymatic diversity. Our structural analyses also demonstrate that self-intoxication is prevented by the immunity protein through direct occlusion of the effector active site. This work significantly expands our current understanding of T6S effector diversity.
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89
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Fritsch MJ, Trunk K, Diniz JA, Guo M, Trost M, Coulthurst SJ. Proteomic identification of novel secreted antibacterial toxins of the Serratia marcescens type VI secretion system. Mol Cell Proteomics 2013; 12:2735-49. [PMID: 23842002 PMCID: PMC3790287 DOI: 10.1074/mcp.m113.030502] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
It has recently become apparent that the Type VI secretion system (T6SS) is a complex macromolecular machine used by many bacterial species to inject effector proteins into eukaryotic or bacterial cells, with significant implications for virulence and interbacterial competition. “Antibacterial” T6SSs, such as the one elaborated by the opportunistic human pathogen, Serratia marcescens, confer on the secreting bacterium the ability to rapidly and efficiently kill rival bacteria. Identification of secreted substrates of the T6SS is critical to understanding its role and ability to kill other cells, but only a limited number of effectors have been reported so far. Here we report the successful use of label-free quantitative mass spectrometry to identify at least eleven substrates of the S. marcescens T6SS, including four novel effector proteins which are distinct from other T6SS-secreted proteins reported to date. These new effectors were confirmed as antibacterial toxins and self-protecting immunity proteins able to neutralize their cognate toxins were identified. The global secretomic study also unexpectedly revealed that protein phosphorylation-based post-translational regulation of the S. marcescens T6SS differs from that of the paradigm, H1-T6SS of Pseudomonas aeruginosa. Combined phosphoproteomic and genetic analyses demonstrated that conserved PpkA-dependent threonine phosphorylation of the T6SS structural component Fha is required for T6SS activation in S. marcescens and that the phosphatase PppA can reverse this modification. However, the signal and mechanism of PpkA activation is distinct from that observed previously and does not appear to require cell–cell contact. Hence this study has not only demonstrated that new and species-specific portfolios of antibacterial effectors are secreted by the T6SS, but also shown for the first time that PpkA-dependent post-translational regulation of the T6SS is tailored to fit the needs of different bacterial species.
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90
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Lin JS, Ma LS, Lai EM. Systematic dissection of the agrobacterium type VI secretion system reveals machinery and secreted components for subcomplex formation. PLoS One 2013; 8:e67647. [PMID: 23861778 PMCID: PMC3702570 DOI: 10.1371/journal.pone.0067647] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2012] [Accepted: 05/22/2013] [Indexed: 11/18/2022] Open
Abstract
The type VI secretion system (T6SS) is widely distributed in pathogenic Proteobacteria. Sequence and structural analysis of T6SS reveals a resemblance to the T4 bacteriophage tail, in which an outer sheath structure contracts an internal tube for injecting nucleic acid into bacterial cells. However, the molecular details of how this phage tail-like T6SS structure is assembled in vivo and executed for exoprotein or effector secretion remain largely unknown. Here, we used a systematic approach to identify T6SS machinery and secreted components and investigate the interaction among the putative sheath and tube components of Agrobacterium tumefaciens. We showed that 14 T6SS components play essential roles in the secretion of the T6SS hallmark exoprotein Hcp. In addition, we discovered a novel T6SS exoprotein, Atu4347, that is dispensable for Hcp secretion. Interestingly, Atu4347 and the putative tube components, Hcp and VgrG, are mainly localized in the cytoplasm but also detected on the bacterial surface. Atu4342 (TssB) and Atu4341 (TssC41) interact with and stabilize each other, which suggests that they are functional orthologs of the sheath components TssB (VipA) and TssC (VipB), respectively. Importantly, TssB interacts directly with the three exoproteins (Hcp, VgrG, and Atu4347), in which Hcp also interacts directly with VgrG-1 on co-purification from Escherichia coli. Further co-immunoprecipitation and pulldown assays revealed these subcomplex(es) in A. tumefaciens and thereby support T6SS functioning as a contractile phage tail-like structure.
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Affiliation(s)
- Jer-Sheng Lin
- Institute of Plant and Microbial Biology, Academia Sinica, Taipei, Taiwan
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91
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Benz J, Reinstein J, Meinhart A. Structural Insights into the Effector - Immunity System Tae4/Tai4 from Salmonella typhimurium. PLoS One 2013; 8:e67362. [PMID: 23826277 PMCID: PMC3695027 DOI: 10.1371/journal.pone.0067362] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2013] [Accepted: 05/17/2013] [Indexed: 11/19/2022] Open
Abstract
Type-6-secretion systems of Gram-negative bacteria are widely distributed needle-like multi-protein complexes that are involved in microbial defense mechanisms. During bacterial competition these injection needles dispense effector proteins into the periplasm of competing bacteria where they induce degradation of the peptidoglycan scaffold and lead to cell lysis. Donor cells co-produce immunity proteins and shuttle them into their own periplasm to prevent accidental toxication by siblings. Recently, a plethora of previously unidentified hydrolases have been suggested to be peptidoglycan degrading amidases. These hydrolases are part of effector/immunity pairs that have been associated with bacterial warfare by type-6-secretion systems. The Tae4 and Tai4 operon encoded by Salmonella typhimurium is one of these newly discovered effector/immunity pairs. The Tae4 effector proteins induce cell lysis by cleaving the γ-D-glutamyl-L-meso-diaminopimelic acid amide bond of acceptor stem muropeptides of the Gram-negative peptidoglycan. Although homologues of the Tae4/Tai4 system have been identified in various different pathogens, little is known about the functional mechanism of effector protein activity and their inhibition by the cognate immunity proteins. Here, we present the high-resolution crystal structure of the effector Tae4 of S. typhimurium in complex with its immunity protein Tai4. We show that Tae4 contains a classical NlpC/P60-peptidase core which is common to other effector proteins of the type-6-secretion system. However, Tae4 has unique structural features that are exclusively conserved within the family of Tae4 effectors and which are important for the substrate specificity. Most importantly, we show that although the overall structure of Tai4 is different to previously described immunity proteins, the essential mode of enzyme inhibition is conserved. Additionally, we provide evidence that inhibition in the Tae4/Tai4 heterotetramer relies on a central Tai4 dimer in order to acquire functionality.
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Affiliation(s)
- Juliane Benz
- Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, Heidelberg, Germany
| | - Jochen Reinstein
- Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, Heidelberg, Germany
| | - Anton Meinhart
- Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, Heidelberg, Germany
- * E-mail:
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92
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Expression of a Yersinia pseudotuberculosis Type VI Secretion System Is Responsive to Envelope Stresses through the OmpR Transcriptional Activator. PLoS One 2013; 8:e66615. [PMID: 23840509 PMCID: PMC3686713 DOI: 10.1371/journal.pone.0066615] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2012] [Accepted: 05/07/2013] [Indexed: 01/06/2023] Open
Abstract
The Type VI secretion system (T6SS) is a macromolecular complex widespread in Gram-negative bacteria. Although several T6SS are required for virulence towards host models, most are necessary to eliminate competitor bacteria. Other functions, such as resistance to amoeba predation, biofilm formation or adaptation to environmental conditions have also been reported. This multitude of functions is reflected by the large repertoire of regulatory mechanisms shown to control T6SS expression, production or activation. Here, we demonstrate that one T6SS gene cluster encoded within the Yersinia pseudotuberculosis genome, T6SS-4, is regulated by OmpR, the response regulator of the two-component system EnvZ-OmpR. We first identified OmpR in a transposon mutagenesis screen. OmpR does not control the expression of the four other Y. pseudotuberculosis T6SS gene clusters and of an isolated vgrG gene, and responds to osmotic stresses to bind to and activate the T6SS-4 promoter. Finally, we show that T6SS-4 promotes Y. pseudotuberculosis survival in high osmolarity conditions and resistance to deoxycholate.
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93
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Braun V, Patzer SI. Intercellular communication by related bacterial protein toxins: colicins, contact-dependent inhibitors, and proteins exported by the type VI secretion system. FEMS Microbiol Lett 2013; 345:13-21. [PMID: 23701660 DOI: 10.1111/1574-6968.12180] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2013] [Revised: 05/15/2013] [Accepted: 05/16/2013] [Indexed: 12/15/2022] Open
Abstract
Bacteria are in constant conflict with competing bacterial and eukaryotic cells. To cope with the various challenges, bacteria developed distinct strategies, such as toxins that inhibit the growth or kill rivals of the same ecological niche. In recent years, two toxin systems have been discovered - the type VI secretion system and the contact-dependent growth inhibition (CDI) system. These systems have structural and functional similarities and share features with the long-known gram-negative bacteriocins, such as small immunity proteins that bind to and inactivate the toxins, and target sites on DNA, tRNA, rRNA, murein (peptidoglycan), or the cytoplasmic membrane. Colicins, CdiA proteins, and certain type VI toxins have a modular design with the transport functions localized in the N-terminal region and the activity functions localized in the C-terminal region. Despite these common properties, the sequences of toxins and immunity proteins of colicins, CDI systems, and type VI systems show little similarity.
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Affiliation(s)
- Volkmar Braun
- Department of Protein Evolution, Max Planck Institute for Developmental Biology, Tübingen, Germany.
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94
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Salomon D, Gonzalez H, Updegraff BL, Orth K. Vibrio parahaemolyticus type VI secretion system 1 is activated in marine conditions to target bacteria, and is differentially regulated from system 2. PLoS One 2013; 8:e61086. [PMID: 23613791 PMCID: PMC3628861 DOI: 10.1371/journal.pone.0061086] [Citation(s) in RCA: 152] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2012] [Accepted: 03/06/2013] [Indexed: 12/21/2022] Open
Abstract
Vibrio parahaemolyticus is a marine bacterium that thrives in warm climates. It is a leading cause of gastroenteritis resulting from consumption of contaminated uncooked shellfish. This bacterium harbors two putative type VI secretion systems (T6SS). T6SSs are widespread protein secretion systems found in many Gram-negative bacteria, and are often tightly regulated. For many T6SSs studied to date, the conditions and cues, as well as the regulatory mechanisms that control T6SS activity are unknown. In this study, we characterized the environmental conditions and cues that activate both V. parahaemolyticus T6SSs, and identified regulatory mechanisms that control T6SS gene expression and activity. We monitored the expression and secretion of the signature T6SS secreted proteins Hcp1 and Hcp2, and found that both T6SSs are differentially regulated by quorum sensing and surface sensing. We also showed that T6SS1 and T6SS2 require different temperature and salinity conditions to be active. Interestingly, T6SS1, which is found predominantly in clinical isolates, was most active under warm marine-like conditions. Moreover, we found that T6SS1 has anti-bacterial activity under these conditions. In addition, we identified two transcription regulators in the T6SS1 gene cluster that regulate Hcp1 expression, but are not required for immunity against self-intoxication. Further examination of environmental isolates revealed a correlation between the presence of T6SS1 and virulence of V. parahaemolyticus against other bacteria, and we also showed that different V. parahaemolyticus isolates can outcompete each other. We propose that T6SS1 and T6SS2 play different roles in the V. parahaemolyticus lifestyles, and suggest a role for T6SS1 in enhancing environmental fitness of V. parahaemolyticus in marine environments when competing for a niche in the presence of other bacterial populations.
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Affiliation(s)
- Dor Salomon
- Department of Molecular Biology, University of Texas Southwestern, Medical Center, Dallas, Texas, United States of America
| | - Herman Gonzalez
- Department of Molecular Biology, University of Texas Southwestern, Medical Center, Dallas, Texas, United States of America
| | - Barrett L. Updegraff
- Department of Molecular Biology, University of Texas Southwestern, Medical Center, Dallas, Texas, United States of America
| | - Kim Orth
- Department of Molecular Biology, University of Texas Southwestern, Medical Center, Dallas, Texas, United States of America
- * E-mail:
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95
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Coulthurst SJ. The Type VI secretion system - a widespread and versatile cell targeting system. Res Microbiol 2013; 164:640-54. [PMID: 23542428 DOI: 10.1016/j.resmic.2013.03.017] [Citation(s) in RCA: 135] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2012] [Accepted: 02/05/2013] [Indexed: 12/31/2022]
Abstract
The Type VI secretion system (T6SS) is the most recently described of the Gram-negative bacterial secretion systems and is widely distributed amongst diverse species. T6SSs are currently believed to be complex molecular machines which inject effector proteins into target cells and which incorporate a bacteriophage-like cell-puncturing device. T6SSs have been implicated in eukaryotic cell targeting and virulence in a range of important pathogens. More recently, 'antibacterial' T6SSs have been reported, which are used to efficiently target competitor bacterial cells by the injection of antibacterial toxins. Although it is clear that T6SSs can be deployed as versatile weapons to compete with other bacteria or attack simple or higher eukaryotes, much remains to be determined about this intriguing system.
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Affiliation(s)
- Sarah J Coulthurst
- Department of Molecular Microbiology, College of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK.
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96
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Carruthers MD, Nicholson PA, Tracy EN, Munson RS. Acinetobacter baumannii utilizes a type VI secretion system for bacterial competition. PLoS One 2013; 8:e59388. [PMID: 23527179 PMCID: PMC3602014 DOI: 10.1371/journal.pone.0059388] [Citation(s) in RCA: 95] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2012] [Accepted: 02/14/2013] [Indexed: 11/18/2022] Open
Abstract
Type VI secretion systems (T6SS) are a class of macromolecular secretion machines that are utilized by a number of bacteria for inter-bacterial competition or to elicit responses in eukaryotic cells. Acinetobacter baumannii is an opportunistic pathogen that causes severe infections in humans. These infections, including pneumonia and bacteremia, are important, as they are often associated with hospitals and medical-settings where they disproportionally affect critically ill patients like those residing in intensive care units. While it is known that A. baumannii genomes carry genes whose predicted products have homology with T6SS-associated gene products from other bacteria, and secretion of a major T6SS structural protein Hcp has been demonstrated, no additional work on an A. baumannii T6SS has been reported. Herein, we demonstrated that A. baumannii strain M2 secretes Hcp and this secretion was dependent upon TssB, an ortholog of a bacteriophage contractile sheath protein, confirming that strain M2 produces a functional T6SS. Additionally, we demonstrated that the ability of strain M2 to out-compete Escherichia coli was reliant upon the products of tssB and hcp. Collectively, our data have provided the first evidence demonstrating function in inter-bacterial competition, for a T6SS produced by A. baumannii.
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Affiliation(s)
- Michael D. Carruthers
- Center for Microbial Pathogenesis, The Research Institute at Nationwide Children’s Hospital and Department of Pediatrics, College of Medicine, The Center for Microbial Interface Biology, The Ohio State University, Columbus, Ohio, United States of America
| | - Paul A. Nicholson
- Center for Microbial Pathogenesis, The Research Institute at Nationwide Children’s Hospital and Department of Pediatrics, College of Medicine, The Center for Microbial Interface Biology, The Ohio State University, Columbus, Ohio, United States of America
| | - Erin N. Tracy
- Center for Microbial Pathogenesis, The Research Institute at Nationwide Children’s Hospital and Department of Pediatrics, College of Medicine, The Center for Microbial Interface Biology, The Ohio State University, Columbus, Ohio, United States of America
| | - Robert S. Munson
- Center for Microbial Pathogenesis, The Research Institute at Nationwide Children’s Hospital and Department of Pediatrics, College of Medicine, The Center for Microbial Interface Biology, The Ohio State University, Columbus, Ohio, United States of America
- * E-mail:
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97
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Kapitein N, Mogk A. Deadly syringes: type VI secretion system activities in pathogenicity and interbacterial competition. Curr Opin Microbiol 2013; 16:52-8. [DOI: 10.1016/j.mib.2012.11.009] [Citation(s) in RCA: 71] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2012] [Revised: 11/12/2012] [Accepted: 11/26/2012] [Indexed: 11/26/2022]
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98
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Identification of T6SS-dependent effector and immunity proteins by Tn-seq in Vibrio cholerae. Proc Natl Acad Sci U S A 2013; 110:2623-8. [PMID: 23362380 DOI: 10.1073/pnas.1222783110] [Citation(s) in RCA: 209] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Type VI protein secretion system (T6SS) is important for bacterial competition through contact-dependent killing of competitors. T6SS delivers effectors to neighboring cells and corresponding antagonistic proteins confer immunity against effectors that are delivered by sister cells. Although T6SS has been found in more than 100 gram-negative bacteria including many important human pathogens, few T6SS-dependent effector and immunity proteins have been experimentally determined. Here we report a high-throughput approach using transposon mutagenesis and deep sequencing (Tn-seq) to identify T6SS immunity proteins in Vibrio cholerae. Saturating transposon mutagenesis was performed in wild type and a T6SS null mutant. Genes encoding immunity proteins were predicted to be essential in the wild type but dispensable in the T6SS mutant. By comparing the relative abundance of each transposon mutant in the mutant library using deep sequencing, we identified three immunity proteins that render protection against killing by T6SS predatory cells. We also identified their three cognate T6SS-secreted effectors and show these are important for not only antibacterial and antieukaryotic activities but also assembly of T6SS apparatus. The lipase and muramidase T6SS effectors identified in this study underscore the diversity of T6SS-secreted substrates and the distinctly different mechanisms that target these for secretion by the dynamic T6SS organelle.
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99
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The type VI secretion system encoded in Salmonella pathogenicity island 19 is required for Salmonella enterica serotype Gallinarum survival within infected macrophages. Infect Immun 2013; 81:1207-20. [PMID: 23357385 DOI: 10.1128/iai.01165-12] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Salmonella enterica serotype 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 that S. Gallinarum harbors a type VI secretion system (T6SS) encoded in Salmonella pathogenicity 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 observed in vivo. Expression analyses revealed that SPI-19 T6SS core components are expressed and produced under in vitro bacterial 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 vitro bacterial 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 after Salmonella uptake. Furthermore, infection of RAW264.7 and HD11 macrophages with deletion mutants of SPI-19 or strains with genes encoding specific T6SS core components (clpV and vgrG) revealed that SPI-19 T6SS contributes to S. Gallinarum survival within macrophages at 20 h postuptake. SPI-19 T6SS function was not linked to Salmonella-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 by Salmonella to survive within host cells.
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