Editing Secretion (section)

===Type VI secretion system (T6SS)===
{{Main|Type VI secretion system}}

Type VI secretion systems were originally identified in 2006 by the group of [[John Mekalanos]] at the Harvard Medical School (Boston, USA) in two bacterial pathogens, ''[[Vibrio cholerae]]'' and ''[[Pseudomonas aeruginosa]]''.<ref name="pmid16432199">{{cite journal | vauthors = Pukatzki S, Ma AT, Sturtevant D, Krastins B, Sarracino D, Nelson WC, Heidelberg JF, Mekalanos JJ | title = Identification of a conserved bacterial protein secretion system in Vibrio cholerae using the Dictyostelium host model system | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 103 | issue = 5 | pages = 1528–33 | date = January 2006 | pmid = 16432199 | pmc = 1345711 | doi = 10.1073/pnas.0510322103 | bibcode = 2006PNAS..103.1528P | jstor = 30048406 | doi-access = free }}</ref><ref name="pmid16763151">{{cite journal | vauthors = Mougous JD, Cuff ME, Raunser S, Shen A, Zhou M, Gifford CA, Goodman AL, Joachimiak G, Ordoñez CL, Lory S, Walz T, Joachimiak A, Mekalanos JJ | title = A virulence locus of Pseudomonas aeruginosa encodes a protein secretion apparatus | journal = Science | volume = 312 | issue = 5779 | pages = 1526–30 | date = June 2006 | pmid = 16763151 | pmc = 2800167 | doi = 10.1126/science.1128393 | bibcode = 2006Sci...312.1526M }}</ref> These were identified when mutations in the Hcp and VrgG genes in ''Vibrio cholerae'' led to decreased virulence and pathogenicity. Since then, Type VI secretion systems have been found in a quarter of all proteobacterial genomes, including animal, plant, human pathogens, as well as soil, environmental or marine bacteria.<ref name="pmid18289922">{{cite journal | vauthors = Bingle LE, Bailey CM, Pallen MJ | title = Type VI secretion: a beginner's guide | journal = Current Opinion in Microbiology | volume = 11 | issue = 1 | pages = 3–8 | date = February 2008 | pmid = 18289922 | doi = 10.1016/j.mib.2008.01.006 | url = http://sure.sunderland.ac.uk/id/eprint/3062/2/pallen_t6ss_2007_revised.pdf }}</ref><ref name="pmid18617888">{{cite journal | vauthors = Cascales E | title = The type VI secretion toolkit | journal = EMBO Reports | volume = 9 | issue = 8 | pages = 735–41 | date = August 2008 | pmid = 18617888 | pmc = 2515208 | doi = 10.1038/embor.2008.131 }}</ref> While most of the early studies of Type VI secretion focused on its role in the pathogenesis of higher organisms, more recent studies suggested a broader physiological role in defense against simple eukaryotic predators and its role in inter-bacteria interactions.<ref>{{cite journal | vauthors = Schwarz S, Hood RD, Mougous JD | title = What is type VI secretion doing in all those bugs? | journal = Trends in Microbiology | volume = 18 | issue = 12 | pages = 531–7 | date = December 2010 | pmid = 20961764 | pmc = 2991376 | doi = 10.1016/j.tim.2010.09.001 }}</ref><ref name="Coulthurst 2013 S0923-2508">{{cite journal | vauthors = Coulthurst SJ | title = The Type VI secretion system - a widespread and versatile cell targeting system | journal = Research in Microbiology | volume = 164 | issue = 6 | pages = 640–54 | year = 2013 | pmid = 23542428 | doi = 10.1016/j.resmic.2013.03.017 | doi-access = free }}</ref> The Type VI secretion system gene clusters contain from 15 to more than 20 genes, two of which, Hcp and VgrG, have been shown to be nearly universally secreted substrates of the system. Structural analysis of these and other proteins in this system bear a striking resemblance to the tail spike of the T4 phage, and the activity of the system is thought to functionally resemble phage infection.<ref name="Silverman 2012 453-472">{{cite journal | vauthors = Silverman JM, Brunet YR, Cascales E, Mougous JD | title = Structure and regulation of the type VI secretion system | journal = Annual Review of Microbiology | volume = 66 | pages = 453–72 | year = 2012 | pmid = 22746332 | pmc = 3595004 | doi = 10.1146/annurev-micro-121809-151619 }}</ref>