The Agrobacterium Type VI Secretion System: A Contractile Nanomachine for Interbacterial Competition

  • Chih-Feng Wu
  • Delaney A. Smith
  • Erh-Min Lai
  • Jeff H. ChangEmail author
Part of the Current Topics in Microbiology and Immunology book series (CT MICROBIOLOGY, volume 418)


The bacterial type VI secretion system (T6SS) is a contractile nanomachine dedicated to delivering molecules out of bacterial cells. T6SS-encoding loci are in the genome sequences of many Gram-negative bacteria, and T6SS has been implicated in a plethora of roles. In the majority of cases, the T6SSs deliver effector proteins in a contact-dependent manner to antagonize other bacteria. Current models suggest that the effectors are deployed to influence social interactions in microbial communities. In this chapter, we describe the structure, function, and regulation of the T6SS and its effectors. We provide focus on the T6SS of Agrobacterium tumefaciens, the causative agent of crown gall disease, and relate the role of the T6SS to the ecology of A. tumefaciens.



We thank members of the Chang lab for their stimulating discussions and insightful comments on the manuscript. We thank Dr. Devanand D Bondage for giving us permission to use his illustration. Work in the Chang lab is supported in part by the National Institute of Food and Agriculture, US Department of Agriculture award 2014-51181-22384. Funding for the Lai lab is provided by the Ministry of Science and Technology of Taiwan (MOST 104-2311-B-001-025-MY3). DAS is a 2018 Barry Goldwater Scholar.


  1. Alteri CJ, Himpsl SD, Pickens SR, Lindner JR, Zora JS, Miller JE, Arno PD, Straight SW, Mobley HL (2013) Multicellular bacteria deploy the type VI secretion system to preemptively strike neighboring cells. PLoS Pathog 9:e1003608CrossRefGoogle Scholar
  2. Barton IS, Fuqua C, Platt TG (2018) Ecological and evolutionary dynamics of a model facultative pathogen: Agrobacterium and crown gall disease of plants. Environ Microbiol 20:16–29CrossRefGoogle Scholar
  3. Basler VA (2016) Type VI secretion system substrates are transferred and reused among sister cells. Cell 167:99–110CrossRefGoogle Scholar
  4. Basler M (2015) Type VI secretion system: secretion by a contractile nanomachine. Philos Trans R Soc Lond B Biol Sci 370:20150021CrossRefGoogle Scholar
  5. Basler M, Pilhofer M, Henderson GP, Jensen GJ, Mekalanos JJ (2012) Type VI secretion requires a dynamic contractile phage tail-like structure. Nature 483:182–186CrossRefGoogle Scholar
  6. Bernal P, Allsopp LP, Filloux A, Llamas MA (2017) The Pseudomonas putida T6SS is a plant warden against phytopathogens. ISME J 11:972–987CrossRefGoogle Scholar
  7. Bladergroen MR, Badelt K, Spaink HP (2003) Infection-blocking genes of a symbiotic Rhizobium leguminosarum strain that are involved in temperature-dependent protein secretion. Mol Plant-Microbe Interact 16:53–64CrossRefGoogle Scholar
  8. Bondage DD, Lin JS, Ma LS, Kuo CH, Lai EM (2016) 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 113:E3931–E3940CrossRefGoogle Scholar
  9. Bonemann G, Pietrosiuk A, Mogk A (2010) Tubules and donuts: a type VI secretion story. Mol Microbiol 76:815–821CrossRefGoogle Scholar
  10. Borenstein DB, Ringel P, Basler M, Wingreen NS (2015) Established microbial colonies can survive Type VI secretion assault. PLoS Comp Bio 11:e1004520CrossRefGoogle Scholar
  11. Borgeaud S, Metzger LC, Scrignari T, Blokesch M (2015) The type VI secretion system of Vibrio cholerae fosters horizontal gene transfer. Science 347:63–67CrossRefGoogle Scholar
  12. Boyer F, Fichant G, Berthod J, Vandenbrouck Y, Attree I (2009) Dissecting the bacterial type VI secretion system by a genome wide in silico analysis: what can be learned from available microbial genomic resources? BMC Genom 10:104CrossRefGoogle Scholar
  13. Brunet Y, Zoued A, Boyer F, Douzi B, Cascales E (2015) The Type VI secretion TssEFGK-VgrG phage-like baseplate is recruited to the TssJLM membrane complex via multiple contacts and serves as assembly platform for tail tube/sheath polymerization. PLoS Genet 11:e1005545CrossRefGoogle Scholar
  14. Burkinshaw BJ, Liang X, Wong M, Le ANH, Lam L, Dong TG (2018) A type VI secretion system effector delivery mechanism dependent on PAAR and a chaperone-co-chaperone complex. Nat Microbiol 3:632–640CrossRefGoogle Scholar
  15. Canfield ML, Moore LW (1991) Isolation and characterization of opine-utilizing strains of Agrobacterium tumefaciens and fluorescent strains of Pseudomonas spp. from rootstocks of Malus. Phytopathol 81:440–443CrossRefGoogle Scholar
  16. Carruthers MD, Nicholson PA, Tracy EN, Munson RS Jr (2013) Acinetobacter baumannii utilizes a type VI secretion system for bacterial competition. PLoS ONE 8:e59388CrossRefGoogle Scholar
  17. Chang JH, Desveaux D, Creason AL (2014) The ABCs and 123 s of bacterial secretion systems in plant pathogenesis. Annu Rev Phytopathol 52:317–345CrossRefGoogle Scholar
  18. Chatzidaki-Livanis M, Geva-Zatorsky N, Comstock LE (2016) Bacteroides fragilis type VI secretion systems use novel effector and immunity proteins to antagonize human gut Bacteroidales species. Proc Natl Acad Sci U S A 113:3627–3632CrossRefGoogle Scholar
  19. Chen H, Yang D, Han F, Tan J, Zhang L, Xiao J, Zhang Y, Liu Q (2017) The bacterial T6SS effector EvpP prevents NLRP3 inflammasome activation by inhibiting the Ca2+-dependent MAPK-Jnk pathway. Cell Host Microbe 21:47–58CrossRefGoogle Scholar
  20. Chen WJ, Kuo TY, Hsieh FC, Chen PY, Wang CS, Shih YL, Lai YM, Liu JR, Yang YL, Shih MC (2016) Involvement of type VI secretion system in secretion of iron chelator pyoverdine in Pseudomonas taiwanensis. Sci Rep 6:32950CrossRefGoogle Scholar
  21. Cianfanelli FR, Alcoforado Diniz J, Guo M, De Cesare V, Trost M, Coulthurst SJ (2016a) VgrG and PAAR proteins define distinct versions of a functional type VI secretion system. PLoS Pathog 12:e1005735CrossRefGoogle Scholar
  22. Cianfanelli FR, Monlezun L, Coulthurst SJ (2016b) Aim, load, fire: the type VI secretion system, a bacterial nanoweapon. Trends Microbiol 24:51–62CrossRefGoogle Scholar
  23. Costechareyre D, Rhouma A, Lavire C, Portier P, Chapulliot D, Bertolla F, Boubaker A, Dessaux Y, Nesme X (2010) Rapid and efficient identification of Agrobacterium species by recA allele analysis: Agrobacterium recA diversity. Microb Ecol 60:862–872CrossRefGoogle Scholar
  24. Driscoll WW, Pepper JW (2010) Theory for the evolution of diffusible external goods. Evolution 64:2682–2687CrossRefGoogle Scholar
  25. Durand E, Cambillau C, Cascales E, Journet L (2014) VgrG, Tae, Tle, and beyond: the versatile arsenal of Type VI secretion effectors. Trends Microbiol 22:498–507CrossRefGoogle Scholar
  26. English G, Trunk K, Rao VA, Srikannathasan V, Hunter WN, Coulthurst SJ (2012) New secreted toxins and immunity proteins encoded within the Type VI secretion system gene cluster of Serratia marcescens. Mol Microbiol 86:921–936CrossRefGoogle Scholar
  27. Faist H, Keller A, Hentschel U, Deeken R (2016) Grapevine (Vitis vinifera) Crown galls host distinct microbiota. Appl Environ Microbiol 82:5542–5552CrossRefGoogle Scholar
  28. Farrand SK, Van Berkum PB, Oger P (2003) Agrobacterium is a definable genus of the family Rhizobiaceae. Int J Syst Evol Microbiol 53:1681–1687CrossRefGoogle Scholar
  29. Felisberto-Rodrigues C, Durand E, Aschtgen MS, Blangy S, Ortiz-Lombardia M, Douzi B, Cambillau C, Cascales E (2011) Towards a structural comprehension of bacterial type VI secretion systems: characterization of the TssJ-TssM complex of an Escherichia coli pathovar. PLoS Pathog 7:e1002386CrossRefGoogle Scholar
  30. Gelvin SB (2000) Agrobacterium and plant genes involved in T-DNA transfer and integration. Annu Rev Plant Mol Biol 51:223–256CrossRefGoogle Scholar
  31. Heckel BC, Tomlinson AD, Morton ER, Choi JH, Fuqua C (2014) Agrobacterium tumefaciens exoR controls acid response genes and impacts exopolysaccharide synthesis, horizontal gene transfer, and virulence gene expression. J Bacteriol 196:3221–3233CrossRefGoogle Scholar
  32. Hood RD et al (2010) A type VI secretion system of Pseudomonas aeruginosa targets a toxin to bacteria. Cell Host Microbe 7:25–37CrossRefGoogle Scholar
  33. Hsu F, Schwarz S, Mougous JD (2009) TagR promotes PpkA-catalysed type VI secretion activation in Pseudomonas aeruginosa. Mol Microbiol 72:1111–1125CrossRefGoogle Scholar
  34. Julou T, Mora T, Guillon L, Croquette V, Schalk IJ, Bensimon D, Desprat N (2013) Cell-cell contacts confine public goods diffusion inside Pseudomonas aeruginosa clonal microcolonies. Proc Natl Acad Sci U S A 110:12577–12582CrossRefGoogle Scholar
  35. Kapitein N, Bonemann G, Pietrosiuk A, Seyffer F, Hausser I, Locker JK, Mogk A (2013) ClpV recycles VipA/VipB tubules and prevents non-productive tubule formation to ensure efficient type VI protein secretion. Mol Microbiol 87:1013–1028CrossRefGoogle Scholar
  36. Kirchberger PC, Unterweger D, Provenzano D, Pukatzki S, Boucher Y (2017) Sequential displacement of Type VI Secretion System effector genes leads to evolution of diverse immunity gene arrays in Vibrio cholerae. Sci Rep 7:45133CrossRefGoogle Scholar
  37. Lassalle F et al (2011) Genomic species are ecological species as revealed by comparative genomics in Agrobacterium tumefaciens. Genome Bio Evol 3:762–781CrossRefGoogle Scholar
  38. Leiman PG, Basler M, Ramagopal UA, Bonanno JB, Sauder JM, Pukatzki S, Burley SK, Almo SC, Mekalanos JJ (2009) Type VI secretion apparatus and phage tail-associated protein complexes share a common evolutionary origin. Proc Natl Acad Sci U S A 106:4154–4159CrossRefGoogle Scholar
  39. Li L, Jia Y, Hou Q, Charles TC, Nester EW, Pan SQ (2002) A global pH sensor: Agrobacterium sensor protein ChvG regulates acid-inducible genes on its two chromosomes and Ti plasmid. Proc Natl Acad Sci U S A 99:12369–12374CrossRefGoogle Scholar
  40. Lin J, Zhang W, Cheng J, Yang X, Zhu K, Wang Y, Wei G, Qian PY, Luo Z, Shen X (2017) A Pseudomonas T6SS effector recruits PQS-containing outer membrane vesicles for iron acquisition. Nat Commun 8:14888CrossRefGoogle Scholar
  41. Lin J, Ma LS, Lai EM (2013) Systematic dissection of the Agrobacterium type VI secretion system reveals machinery and secreted components for subcomplex formation. PLoS ONE 8:e67647CrossRefGoogle Scholar
  42. Lin JS, Pissaridou P, Wu HH, Tsai MD, Filloux A, Lai EM (2018) TagF-mediated repression of bacterial type VI secretion systems involves a direct interaction with the cytoplasmic protein Fha. J Biol Chem. (In press)Google Scholar
  43. Lin JS, Wu HH, Hsu PH, Ma LS, Pang YY, Tsai MD, Lai EM (2014) Fha interaction with phosphothreonine of TssL activates type VI secretion in Agrobacterium tumefaciens. PLoS Pathog 10:e1003991CrossRefGoogle Scholar
  44. Lossi NS, Manoli E, Forster A, Dajani R, Pape T, Freemont P, Filloux A (2013) The HsiB1C1 (TssB-TssC) complex of the Pseudomonas aeruginosa type VI secretion system forms a bacteriophage tail sheathlike structure. J Biol Chem 288:7536–7548CrossRefGoogle Scholar
  45. Ma AT, Mekalano J (2010) In vivo actin cross-linking induced by Vibrio cholerae type VI secretion system is associated with intestinal inflammation. Proc Natl Acad Sci U S A 107:4365–4370CrossRefGoogle Scholar
  46. Ma LS, Hachani A, Lin JS, Filloux A, Lai EM (2014) Agrobacterium tumefaciens deploys a superfamily of type VI secretion DNase effectors as weapons for interbacterial competition in planta. Cell Host Microbe 16:94–104CrossRefGoogle Scholar
  47. Ma LS, Lin J, Lai EM (2009) An IcmF family protein, ImpLM, is an integral inner membrane protein interacting with ImpKL, and its walker a motif is required for type VI secretion system-mediated Hcp secretion in Agrobacterium tumefaciens. J Bacteriol 191:4316–4329CrossRefGoogle Scholar
  48. McNally L, Bernardy E, Thomas J, Kalziqi A, Pentz J, Brown SP, Hammer BK, Yunker PJ, Ratcliff WC (2017) Killing by Type VI secretion drives genetic phase separation and correlates with increased cooperation. Nat Commun 8:14371CrossRefGoogle Scholar
  49. Miyata ST, Bachmann V, Pukatzki S (2013) Type VI secretion system regulation as a consequence of evolutionary pressure. J Med Microbiol 62:663–676CrossRefGoogle Scholar
  50. Mougous JD et al (2006) A virulence locus of Pseudomonas aeruginosa encodes a protein secretion apparatus. Science 312:1526–1530CrossRefGoogle Scholar
  51. Mougous JD, Gifford CA, Ramsdell TL, Mekalanos JJ (2007) Threonine phosphorylation post-translationally regulates protein secretion in Pseudomonas aeruginosa. Nat Cell Biol 9:797–803CrossRefGoogle Scholar
  52. Nadell CD, Foster KR, Xavier JB (2010) Emergence of spatial structure in cell groups and the evolution of cooperation. PLoS Comput Biol 6:e1000716CrossRefGoogle Scholar
  53. Nadell CD, Drescher K, Foster KR (2016) Spatial structure, cooperation and competition in biofilms. Nat Rev Microbiol 14:589–600CrossRefGoogle Scholar
  54. Planamente S, Salih O, Manoli E, Albesa-Jove D, Freemont PS, Filloux A (2016) TssA forms a gp6-like ring attached to the type VI secretion sheath. EMBO J 35:1613–1627CrossRefGoogle Scholar
  55. Pukatzki S, Ma AT, Revel AT, Sturtevant D, Mekalanos JJ (2007) Type VI secretion system translocates a phage tail spike-like protein into target cells where it cross-links actin. Proc Natl Acad Sci U S A 104:15508–15513CrossRefGoogle Scholar
  56. Pukatzki S, Ma AT, Sturtevant D, Krastins B, Sarracino D, Nelson WC, Heidelberg JF, Mekalanos JJ (2006) Identification of a conserved bacterial protein secretion system in Vibrio cholerae using the Dictyostelium host model system. Proc Natl Acad Sci U S A 103:1528–1533CrossRefGoogle Scholar
  57. Rao PS, Yamada Y, Tan YP, Leung KY (2004) Use of proteomics to identify novel virulence determinants that are required for Edwardsiella tarda pathogenesis. Mol Microbiol 53:573–586CrossRefGoogle Scholar
  58. Rigard M et al (2016) Francisella tularensis IglG belongs to a novel family of PAAR-like T6SS proteins and harbors a unique N-terminal extension required for virulence. PLoS Pathog 12:e1005821CrossRefGoogle Scholar
  59. Roest HP, Mulders IH, Spaink HP, Wijffelman CA, Lugtenberg BJ (1997) A Rhizobium leguminosarum biovar trifolii locus not localized on the sym plasmid hinders effective nodulation on plants of the pea cross-inoculation group. Mol Plant-Microbe Interact 10:938–941CrossRefGoogle Scholar
  60. Russell AB, Hood RD, Bui NK, LeRoux M, Vollmer W, Mougous JD (2011) Type VI secretion delivers bacteriolytic effectors to target cells. Nature 475:343–347CrossRefGoogle Scholar
  61. Russell A, LeRoux M, Hathazi K, Agnello DM, Ishikawa T, Wiggins PA, Wai SN, Mougous JD (2013) Diverse type VI secretion phospholipases are functionally plastic antibacterial effectors. Nature 496:508–512CrossRefGoogle Scholar
  62. Russell AB, Peterson SB, Mougous JD (2014) Type VI secretion system effectors: poisons with a purpose. Nat Rev Microbiol 12:137–148CrossRefGoogle Scholar
  63. Sana TG, Flaugnatti N, Lugo KA, Lam LH, Jacobson A, Baylot V, Durand E, Journet L, Cascales E, Monack DM (2016) Salmonella Typhimurium utilizes a T6SS-mediated antibacterial weapon to establish in the host gut. Proc Natl Acad Sci U S A 113:E5044–E5051CrossRefGoogle Scholar
  64. Schlieker C, Zentgraf H, Dersch P, Mogk A (2005) ClpV, a unique Hsp100/Clp member of pathogenic proteobacteria. Biol Chem 386:115–1127CrossRefGoogle Scholar
  65. Schwarz S, West TE, Boyer F, Chiang WC, Carl MA, Hood RD, Rohmer L, Tolker-Nielsen T, Skerrett SJ, Mougous JD (2010) Burkholderia type VI secretion systems have distinct roles in eukaryotic and bacterial cell interactions. PLoS Pathog 6:e1001068CrossRefGoogle Scholar
  66. Shalom G, Shaw JG, Thomas MS (2007) In vivo expression technology identifies a type VI secretion system locus in Burkholderia pseudomallei that is induced upon invasion of macrophages. Microbiology 153:2689–2699CrossRefGoogle Scholar
  67. Shneider MM, Buth SA, Ho BT, Basler M, Mekalanos JJ, Leiman PG (2013) PAAR-repeat proteins sharpen and diversify the type VI secretion system spike. Nature 500:350–353CrossRefGoogle Scholar
  68. Si M, Zhao C, Burkinshaw B, Zhang B, Wei D, Wang Y, Dong TG, Shen X (2017) Manganese scavenging and oxidative stress response mediated by type VI secretion system in Burkholderia thailandensis. Proc Natl Acad Sci U S A 114:E2233–e2242CrossRefGoogle Scholar
  69. Silverman JM, Agnello DM, Zheng H, Andrews BT, Li M, Catalano CE, Gonen T, Mougous JD (2013) Haemolysin coregulated protein is an exported receptor and chaperone of type VI secretion substrates. Mol Cell 51:584–593CrossRefGoogle Scholar
  70. Slater SC et al (2009) Genome sequences of three agrobacterium biovars help elucidate the evolution of multichromosome genomes in bacteria. J Bacteriol 191:2501–2511CrossRefGoogle Scholar
  71. Stachel SE, Messens E, Montagu MV, Zambryski P (1985) Identification of the signal molecules produced by wounded plant cells that activate T-DNA transfer in Agrobacterium tumefaciens. Nature 318:624–629CrossRefGoogle Scholar
  72. Suarez G, Sierra JC, Erova TE, Sha J, Horneman AJ, Chopra AK (2010) A type VI secretion system effector protein, VgrG1, from Aeromonas hydrophila that induces host cell toxicity by ADP ribosylation of actin. J Bacteriol 192:155–168CrossRefGoogle Scholar
  73. Thomas J, Watve SS, Ratcliff WC, Hammer BK (2017) Horizontal gene transfer of functional Type VI killing genes by natural transformation. mBio 8:e00654–17CrossRefGoogle Scholar
  74. Unterweger D, Kostiuk, Otjengerdes R, Wilton A, Diaz-Satizabal L, Pukatzki S (2015) Chimeric adaptor proteins translocate diverse type VI secretion system effectors in Vibrio cholerae. EMBO J 34:2198–2210CrossRefGoogle Scholar
  75. Wang T et al (2015) Type VI secretion system transports Zn2+ to combat multiple stresses and host immunity. PLoS Pathog 11:e1005020CrossRefGoogle Scholar
  76. Wong M, Liang X, Smart M, Tang L, Moore R, Ingalls B, Dong TG (2016) Microbial her protection mediated by antagonistic interaction in polymicrobial communities. Appl Environ Microbiol 82:6881–6888CrossRefGoogle Scholar
  77. Wu CF, Lin JS, Shaw GC, Lai EM (2012) Acid-induced type VI secretion system is regulated by ExoR-ChvG/ChvI signaling cascade in Agrobacterium tumefaciens. PLoS Pathog 8:e1002938CrossRefGoogle Scholar
  78. Wu HY, Chung PC, Shih HW, Wen S, Lai EM (2008) Secretome analysis uncovers an Hcp-family protein secreted via a type VI secretion system in Agrobacterium tumefaciens. J Bacteriol 190:2841–2850CrossRefGoogle Scholar
  79. Yuan ZC, Liu P, Saenkham P, Kerr K, Nester EW (2008) Transcriptome profiling and functional analysis of Agrobacterium tumefaciens reveals a general conserved response to acidic conditions (pH 5.5) and a complex acid-mediated signaling involved in Agrobacterium-plant interactions. J Bacteriol 190:494–507CrossRefGoogle Scholar
  80. Zheng J, Ho B, Mekalanos JJ (2011) Genetic analysis of anti-amoebae and anti-bacterial activities of the type VI secretion system in Vibrio cholerae. PLoS ONE 6:e23876CrossRefGoogle Scholar
  81. Zoued A, Brunet YR, Durand E, Aschtgen MS, Logger L, Douzi B, Journet L, Cambillau C, Cascales E (2014) Architecture and assembly of the Type VI secretion system. Biochimi Biophys Acta 1843:1664–1673CrossRefGoogle Scholar

Copyright information

© Springer International Publishing AG, part of Springer Nature 2018

Authors and Affiliations

  • Chih-Feng Wu
    • 1
  • Delaney A. Smith
    • 1
  • Erh-Min Lai
    • 2
  • Jeff H. Chang
    • 1
    • 3
    Email author
  1. 1.Department of Botany and Plant PathologyOregon State UniversityCorvallisUSA
  2. 2.Institute of Plant and Microbial Biology, Academia SinicaTaipeiTaiwan
  3. 3.Center for Genome Research and Biocomputing, Oregon State UniversityCorvallisUSA

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