Abstract

Secretion systems allow bacteria to transport macromolecules such as proteins into host cells during pathogenesis or bacterial cells during competition in various ecological settings. Type VI Secretion Systems (T6SS) are encoded by a cluster of 15-20 genes that is present in at least one copy in approximately 25% of all sequenced Gram-negative bacteria. Several T6SS components are structural homologs of components of a contractile bacteriophage tail and assemble into a large structure that can be studied using whole cell electron cryo tomography and live cell fluorescence microscopy. A combination of these techniques allows to obtain high resolution structure of T6SS in situ and to follow T6SS assembly in time. This provides an unprecedented level of understanding of this dynamic nanomachine. I will discuss structure, function and dynamics of T6SS in various model organisms as well as a mechanism of T6SS activation and substrate delivery.