A Type VI Secretion-Related Pathway in Bacteroidetes Mediates Interbacterial Antagonism

Alistair B. Russell, Aaron G. Wexler, Brittany N. Harding, John C. Whitney, Alan J. Bohn, Young Ah Goo, Bao Q. Tran, Natasha A. Barry, Hongjin Zheng, S. Brook Peterson, Seemay Chou, Tamir Gonen, David R. Goodlett, Andrew L. Goodman, and Joseph D. Mougous

Cell Host & Microbe 16, 227–236, August 13, 2014

Speaker: Meng-Ju Tsai (蔡孟儒)                                                  Time: 15:00~16:00, Dec 03, 2014

Commentator: Dr. I-Hsiu Huang (黃一修 老師)                    Place: Room 601

Abstract:

    Strains of Bacteroidetes, a phylum of Gram-negative bacteria, inhabit the gastrointestinal (GI) tract acting as mutualists in human or other mammals [1]. It has been demostrated that the pathogenic bacteria of the phylum Proteobacteria can utilize Type VI Secretion System (T6SS), which enables the Gram-negative bacteria to translocate substrates to a wide range of recipient cell, to compete with other bacteria for reducing competition from other bacteria. [2, 3]. However, it is not clear how stranis of Bacteroidetes, which are also Gram-negative, survive in a polymicrobial environment in GI tract. The authors hypothesized that Bacteroidetes may also utilize T6SS to compete with other bacteria. They first identified a cluster of genes encoding homologues of Proteobacterial T6SS-related proteins, including the T6SS core ATPase, ClpV, and core elements TssB, TssC, TssE, TssF, TssG, and TssK in Bacteroidetes species Bacteroides fagilis,Flavobacterium johnsoniae and Prevotella veroralis. They then used F. johnsoniae, a soil-associated bacterium, to determine the secretome of T6SS and the interphyla bacterial antagonism. They found that the Flavobacterium type VI secretion effector 1 (Fte1) induced cell lysis of E. coli, and F. johnsoniae used T6SS to inhibit the growth of pathogens Burkholderia thailandensis andPseudomonas putida in coculture. They further found that B. fragilis can reduce the growth of another human gut commensal B. thetaiotaomicron, which lacks a T6SS. Collectively, strains of Bacteroidetes can utilize T6SS to export antibacterial proteins to the competitor bacteria, and this may be the reason why the microbiota in GI tract can act as the barrier against pathogens.

References:

1.         Lozupone, C.A., Stombaugh, J.I., Gordon, J.I., Jansson, J.K., and Knight, R. (2012). Diversity, stability and resilience of the human gut microbiota. Nature 489, 220–230.

2.         Braun V, Pilsl H, and Groß P. (1994). Colicins: structures, modes of actions, transfer through membranes, and evolution. Arch. Microbiol. 161:199–206

3.         Riley, M.A., and Wertz, J.E. (2002). Bacteriocins: evolution, ecology, and application. Annu. Rev. Microbiol. 56, 117–137.