The experiment was repeated three times. Uninfected cells lysed in PBS with 0.1% deoxycholate served as a positive control and was arbitrarily set as 100%; the results were expressed relative to the positive control. Data analysis and statistical methods Statistical significances were determined using paired, two-tailed Student’s t-tests. Acknowledgements We thank Lenore Johansson for assistance with the electron microscopy, Kun Sun #4SC-202 randurls[1|1|,|CHEM1|]# for help with generating constructs for the bacterial 2-hybrid assay, and Konstantin Kadzhaev for aid with constructing the primers for the pdpC deletion mutant. This work was supported by grant 2009-5026 from the Swedish

Research Council and a grant from the Medical Faculty, Umeå University, Umeå, Sweden. The work was performed in part at the Umeå Centre for Microbial Research (UCMR). Electronic supplementary material Additional file 1: Table S1: Stress sensitivity tests; Table S2. Bacterial strains and plasmids; Table S3. Primers used in this study. (DOC 160 KB) References 1. Bingle LE, Bailey CM, Pallen MJ: Type VI secretion: a beginner’s guide. Curr Opin Microbiol 2008,11(1):3–8.PubMedCrossRef 2. Boyer F, Fichant G, Berthod J, Vandenbrouck Y, Attree I: Dissecting the bacterial type VI secretion system by a genome wide in silico analysis: what can

be learned from available microbial genomic resources? BMC Genomics 2009,10(104):104.PubMedCrossRef 3. Filloux A: The type VI secretion system: a tubular story. EMBO J 2009,28(4):309–310.PubMedCrossRef 4. Hood RD, Singh P, Hsu F, Guvener T, Carl MA, Trinidad Protein Tyrosine Kinase inhibitor RR, Silverman JM, Ohlson BB, Hicks KG, Plemel RL, et al.: A type VI secretion system of Pseudomonas aeruginosa targets a toxin to bacteria. Cell Host Microbe 2010,7(1):25–37.PubMedCrossRef 4-Aminobutyrate aminotransferase 5. Murdoch SL, Trunk K, English G, Fritsch MJ, Pourkarimi E, Coulthurst SJ: The opportunistic

pathogen Serratia marcescens utilizes type VI secretion to target bacterial competitors. J Bacteriol 2011,193(21):6057–6069.PubMedCrossRef 6. Russell AB, Hood RD, Bui NK, LeRoux M, Vollmer W, Mougous JD: Type VI secretion delivers bacteriolytic effectors to target cells. Nature 2011,475(7356):343–347.PubMedCrossRef 7. Basler M, Pilhofer M, Henderson GP, Jensen GJ, Mekalanos JJ: Type VI secretion requires a dynamic contractile phage tail-like structure. Nature 2012,483(7388):182–186.PubMedCrossRef 8. Oyston PC, Sjöstedt A, Titball RW: Tularaemia: bioterrorism defence renews interest in Francisella tularensis. Nat Rev Microbiol 2004,2(12):967–978.PubMedCrossRef 9. Bröms JE, Sjöstedt A, Lavander M: The role of the Francisella tularensis pathogenicity island in type VI secretion, intracellular survival, and modulation of host cell signaling. Front Microbiol 2010,1(136):136.PubMed 10. Nano FE, Schmerk C: The Francisella pathogenicity island. Ann N Y Acad Sci 2007, 1105:122–137.PubMedCrossRef 11.