The type VI secretion systems (T6SSs) are a class of sophisticated cell contact-dependent apparatuses involved in mediating antagonistic or synergistic interactions between bacteria or between bacteria and eukaryotes. These apparatuses have recently been found to be widely distributed among Gram-negative bacterial species.
To date, only a limited number of databases of T6SSs is available, such as the T6SS core components recorded by KEGG ( and MicrobeWiki ( And HoPaCI-DB provides host-pathogen interaction data from the pathogenic bacteria P. aeruginosa and C. burnetii, including nineteen H1-3 T6SS associated regulation processes in P. aeruginosa.

SecReT6: a web-based resource for type VI secretion systems found in bacteria
The open-access database SecReT6 offers a unique, readily explorable archive of known and putative T6SSs and cognate effectors in bacteria. A broad range of T6SS gene cluster prediction, comparative analyses, similarity searches, phylogenetic analysis, primer design and other functional analysis tools are readily accessible via SecReT6.

SecReT6 v2.0 released on Jun. 28th, 2014.
SecReT6 v2.0 currently contains data on 10,891 core T6SS components belonging to 873 T6SSs found in 478 bacterial strains representing 221 species, as well as a collection of over six hundred associated references. Also collated and archived were 1,277 diverse candidate secreted effectors which were experimentally demonstrated and/or predicted to be delivered by T6SSs into target eukaryotic and/or prokaryote cells as well as 174 immunity proteins.

SecReT6 v1.0 released on Aug. 15th, 2013.
SecReT6 v1.0 contains data on 9,664 core T6SS components mapping to 782 T6SSs found in 431 bacterial strains representing 216 species, as well as a collection of over four hundred directly relevant references.

T6SS conserved components
Table 1. List of core components found in the well-documented T6SS representatives
ComponentFunctionCluster of Orthologous Groups
TssA unknown COG3515
TssB (IglA, VipA) Tubular complex COG3516
TssC (IglB, VipB) Tubular complex COG3517
TssD (Hcp) Hexameric ring COG3157
TssE Cytoplasmic protein COG3518
TssF unknown COG3519
TssG unknown COG3520
TssH (ClpV) ATPase COG0542
TssI (VgrG) Needle-like structure COG3501
TssJ Transmembrane spanning structure COG3521
TssK Cytoplasmic protein COG3522
TssL (DotU) Transmembrane spanning structure COG3455
TssM (IcmF) Transmembrane spanning structure COG3523
More details at the Excel file.

The prediction strategy used by SecReT6 to identify T6SS-encoding loci