Tit-for-Tat: Type VI Secretion System Counterattack during Bacterial Cell-Cell Interactions

Marek Basler, Brian T. Ho, and John J. Mekalanos.  Cell 152, 884–894, February 14, 2013

Speaker: Feng Ru Hung (洪鳳嬬)                    Time: 14:00~15:00, April. 21, 2013

Commentator: Dr. Ching-Hao Teng(鄧景浩 博士)    Place: Room 601

Abstract

    The interactions between bacterial species range from cooperative to competitive, and one of the competitive behaviors is related to type VI secretion system (T6SS). About 25% of all sequenced Gram-negative bacteria possess T6SS gene cluster, which has been implicated in the virulence of several human pathogens¹. This secretion system is a dynamic apparatus that can translocate effector proteins between bacterial cells by using a bacteriophage sheath-like tail. The secretion activity of  T6SS, like sheath extension, contraction and disassembly, can be visualized by time-lapse microscopy with fluoresent fusion proteins. With this technique, the authors have previously found that the Pseudomonas aureginosa cell can repond to the T6SS attack of an adjecent sister cell by increasing its own T6SS activity, and such response is called T6SS dueling. To understand how T6SS dueling is triggered, the authors studied the ability of P. aeruginosa to prey upon T6SS+ and T6SS- Vibrio cholerae and Acinetobacter baylyi. They found that the antibacterial P. aeruginosa T6SS dueling response could specifically target T6SS+ V. cholerae that had attacked P. aeruginosafirst. They further tested whether Tse1, Tse2 and Tse3, the effectors of T6SS², were invoved in dueling. They showed that although P. aeruginosa T6SS delivered Tse effectors into V. cholerae, they were not required for dueling. Finally, they determined whether the TagQRST-PpkA-Fha1-PppA T6SS regulatory system was involved in T6SS dueling, and demonstrated that this signaling cascade was essential for P. aeruginosa T6SS dueling and prey selection. More, T6SS apparatus assembly and lethal counterattack were regulated by a signal triggered at the location attacked by the other aggressive T6SS+ bacterial cell.

References

1. Mougous, J.D. et al. (2007). Threonine phosphorylation post-translationally regulates protein secretion in Pseudomonas aeruginosa. Nat. Cell Biol. 9, 797–803.

2. Russell, A.B. et al. (2011). Type VI secretion delivers bacteriolytic effectors to target cells. Nature 475, 343–347.