The Agrobacterium Type VI Secretion System: A Contractile Nanomachine for Interbacterial Competition
The bacterial type VI secretion system (T6SS) is a contractile nanomachine dedicated to delivering molecules out of bacterial cells. T6SS-encoding loci are in the genome sequences of many Gram-negative bacteria, and T6SS has been implicated in a plethora of roles. In the majority of cases, the T6SSs deliver effector proteins in a contact-dependent manner to antagonize other bacteria. Current models suggest that the effectors are deployed to influence social interactions in microbial communities. In this chapter, we describe the structure, function, and regulation of the T6SS and its effectors. We provide focus on the T6SS of Agrobacterium tumefaciens, the causative agent of crown gall disease, and relate the role of the T6SS to the ecology of A. tumefaciens.
We thank members of the Chang lab for their stimulating discussions and insightful comments on the manuscript. We thank Dr. Devanand D Bondage for giving us permission to use his illustration. Work in the Chang lab is supported in part by the National Institute of Food and Agriculture, US Department of Agriculture award 2014-51181-22384. Funding for the Lai lab is provided by the Ministry of Science and Technology of Taiwan (MOST 104-2311-B-001-025-MY3). DAS is a 2018 Barry Goldwater Scholar.
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