Title: Bacterial warfare mediated by the type VI protein secretion system

Presenter: Dr. Tao Dong

University: University of Calgary, Canada

Time: 10:00-11:00, October 26, 2015

Venue: Room A202, Institute of Microbiology, Chinese Academy of Sciences

Abstract: Microbes employ various attack and defense systems for survival in multispecies communities. However, the strategies utilized by different microbes to coexist despite their antagonistic interactions with other species are not well understood. The type VI secretion system (T6SS) is a lethal weapon Gram-negative bacteria use to deliver toxic effectors to neighboring cells through direct contact. For self-protection, the T6SS deploys immunity proteins to neutralize the toxicity of cognate effectors delivered between sister cells. Identification of effectors is required for understanding the pivotal role that the T6SS plays in dictating interbacterial and bacterial-host dynamics. Here we report a new approach to systematically identify T6SS effectors. We demonstrate that secretion of effectors requires interaction with a set of novel, cognate effector-binding chaperone proteins that we name T6SS effector chaperone (TEC) proteins. The TEC proteins share a highly conserved domain (DUF4123) and are genetically encoded upstream of their cognate effector genes. Using the conserved TEC domain sequence, we identified a large family of TEC genes coupled to putative T6SS effectors in Gram-negative bacteria. We then use a number of T6SS active killer species including Vibrio cholerae, Aeromonas hydrophila, and Acinetobacter baylyi, to demonstrate that T6SS effectors confer protection in interspecies interaction by increasing the competitive fitness of T6SS organisms. Mutants lacking effector proteins are readily killed by competing species. Using time-lapse fluorescence microscopy analysis, we report that the antagonistic interaction mediated by the T6SS drives the formation of clonal single-species clusters from mixed populations, defining the social boundary of a multispecies community. In summary, our results suggest that, “The best defense is a good offence”, a military motto, also applies to the warfare of primitive microbes in complex multispecies environments.

Dong’s lab website: http://ucalgary.ca/donglab/