| Summary: | Type VI secretion systems are bacterial virulence-associated nanomachines composed of proteins that are evolutionarily related to components of bacteriophage tails. Here we show that protein secretion by the type VI secretion system of Vibrio cholerae requires the action of a dynamic intracellular tubular structure that is structurally and functionally homologous to contractile phage tail sheath. Time-lapse fluorescence light microscopy reveals that sheaths of the type VI secretion system cycle between assembly, quick contraction, disassembly and re-assembly. Whole-cell electron cryotomography further shows that the sheaths appear as long tubular structures in either extended or contracted conformations that are connected to the inner membrane by a distinct basal structure. These data support a model in which the contraction of the type VI secretion system sheath provides the energy needed to translocate proteins out of effector cells and into adjacent target cells. © 2012 Macmillan Publishers Limited. Received 03 October 2011. Accepted 09 January 2012. Published online 26 February 2012. We thank T. G. Bernhardt and N. T. Peters for assistance with fluorescence microscopy, discussions and for a gift of plasmids carrying sfGFP and mCherry2 genes. We thank the Nikon Imaging Center at Harvard Medical School for help with fluorescence microscopy, and Research Precision Instruments and Hamamatsu for lending an ORCA-Flash2.8 camera. We thank the Harvard Medical School Electron Microscopy Facility for help with and supervision of transmission electron microscopy. We thank M. K. Waldor for a V. cholerae 2740-80 strain and discussions. We thank D. Ewen Cameron for a knockout construct pWM91-flgG. We thank B. Wen and Z. Li for initial cryotomographic studies. This work was supported by National Institute of Allergy and Infectious Diseases grants AI-018045 and AI-26289 to J.J.M. and National Institute of General Medical Sciences grant GM094800B to G.J.J. Author Contributions: All authors helped design and analyse ...
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