Advances of the Gram-negative bacterial type Ⅵ secretion system and its function for metal ion acquisition

Abstract:

Bacterial secretion systems can deliver specific effector molecular to outer environment or directly into target cells, resulting in the adaptive advantage from interaction between bacteria and host or bacteria in microbial communities. The type Ⅵ secretion system (T6SS) is a macromolecular secretory apparatus which is functionally and structurally analogous to the needle-like contractile tail of bacteriophages, wide-spreading in Gram-negative bacteria. It can translocate diverse enzyme and toxins of bacteria into eukaryotic or prokaryotic target cells in a contact-dependent manner. After delivery, the effector proteins can make an impact on both interbacterial competition and pathogenicity. In addition, some effectors can also enter the extracellular milieu in a non-contact dependent manner to help bacteria obtain scarce metal ions, which is essential for the maintenance of intracellular metal homeostasis under stress conditions. In this review, we summarize the advances in understanding the relevant aspects from the structure and assembly to the function of T6SS. We also focus on the broad area of T6SS effector and its mechanism of metal ion translocation, which contributes to our comprehension of the crucial role of T6SS in the microbial competition and host infection.