T6SSs are toxin delivery systems. It is a multiprotein complex requiring numerous core proteins (Tss proteins) including cytoplasmic, transmembrane, and outer membrane components. The needle or tube apparatus is comprised of a phage-like complex, similar to the T4 contractile bacteriophage tail, which is thought to be anchored to the membrane by a trans-envelope complex [1]. TssN proteins have multiple predicted transmembrane (TM) regions. In Flavobacterium johnsoniae, three specific components (TssN, TssO and TssP) are absent in the other sub-types of T6SS [2].

1: Type VI secretion systems of human gut Bacteroidales segregate into three genetic architectures, two of which are contained on mobile genetic elements. Coyne MJ, Roelofs KG, Comstock LE; BMC Genomics. 2016;17:58. PMID:26768901

2: Identification of protein secretion systems in bacterial genomes. Abby SS, Cury J, Guglielmini J, Neron B, Touchon M, Rocha EP; Sci Rep. 2016;6:23080. PMID:26979785