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PLoS Pathog. 2015 Aug 25;11(8):e1005128. doi: 10.1371/journal.ppat.1005128. eCollection 2015 Aug.

Type VI Secretion System Toxins Horizontally Shared between Marine Bacteria.

Author information

1
Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America.
2
Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America.
3
Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America.
4
Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America; Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America; Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America.
5
Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America; Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America.

Abstract

The type VI secretion system (T6SS) is a widespread protein secretion apparatus used by Gram-negative bacteria to deliver toxic effector proteins into adjacent bacterial or host cells. Here, we uncovered a role in interbacterial competition for the two T6SSs encoded by the marine pathogen Vibrio alginolyticus. Using comparative proteomics and genetics, we identified their effector repertoires. In addition to the previously described effector V12G01_02265, we identified three new effectors secreted by T6SS1, indicating that the T6SS1 secretes at least four antibacterial effectors, of which three are members of the MIX-effector class. We also showed that the T6SS2 secretes at least three antibacterial effectors. Our findings revealed that many MIX-effectors belonging to clan V are "orphan" effectors that neighbor mobile elements and are shared between marine bacteria via horizontal gene transfer. We demonstrated that a MIX V-effector from V. alginolyticus is a functional T6SS effector when ectopically expressed in another Vibrio species. We propose that mobile MIX V-effectors serve as an environmental reservoir of T6SS effectors that are shared and used to diversify antibacterial toxin repertoires in marine bacteria, resulting in enhanced competitive fitness.

PMID:
26305100
PMCID:
PMC4549250
DOI:
10.1371/journal.ppat.1005128
[Indexed for MEDLINE]
Free PMC Article

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