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Type VI Secretion System Toxins Horizontally Shared between Marine Bacteria.

Salomon D, Klimko JA, Trudgian DC, Kinch LN, Grishin NV, Mirzaei H, Orth K - PLoS Pathog. (2015)

Bottom Line: Using comparative proteomics and genetics, we identified their effector repertoires.We also showed that the T6SS2 secretes at least three antibacterial effectors.We demonstrated that a MIX V-effector from V. alginolyticus is a functional T6SS effector when ectopically expressed in another Vibrio species.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Biology, 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.

No MeSH data available.


Related in: MedlinePlus

Antibacterial activities of V. alginolyticus T6SSs are differentially regulated by salinity and temperature.Viability of E. coli prey before (0h) and after (4h) co-culture with indicated V. alginolyticus attacker strains or alone. Co-cultures were incubated for 4 hours on (A) LB or (B) MLB agar plates at 30°C or 37°C. None = medium only. WT = wild-type.
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ppat.1005128.g001: Antibacterial activities of V. alginolyticus T6SSs are differentially regulated by salinity and temperature.Viability of E. coli prey before (0h) and after (4h) co-culture with indicated V. alginolyticus attacker strains or alone. Co-cultures were incubated for 4 hours on (A) LB or (B) MLB agar plates at 30°C or 37°C. None = medium only. WT = wild-type.

Mentions: We previously reported that VaT6SS1 mediates bacterial killing on LB agar plates at 30°C [16]. As V. alginolyticus is a marine bacterium that thrives during warm months under various conditions in the environment and the host [22,28], we set out to determine how environmental conditions such as salinity and temperature affect the activity of VaT6SS1. To this end, we monitored the viability of E. coli before and after co-culture with wild-type V. alginolyticus, a Δhcp1 derivative in which VaT6SS1 is inactive, or alone on LB or MLB plates (containing 1% and 3% NaCl, respectively), at 30°C or 37°C. When co-cultured at 37°C, V. alginolyticus was unable to kill E. coli on LB plates (Fig 1A), but it was able to kill E. coli on MLB plates (Fig 1B). Surprisingly, whereas deletion of hcp1 largely abrogated the antibacterial toxicity of V. alginolyticus on LB at 30°C, it had only a marginal effect when co-cultures were grown on MLB plates at 30°C (Fig 1). This result suggested that there is another antibacterial determinant other than VaT6SS1 that can mediate interbacterial competition under high salt conditions.


Type VI Secretion System Toxins Horizontally Shared between Marine Bacteria.

Salomon D, Klimko JA, Trudgian DC, Kinch LN, Grishin NV, Mirzaei H, Orth K - PLoS Pathog. (2015)

Antibacterial activities of V. alginolyticus T6SSs are differentially regulated by salinity and temperature.Viability of E. coli prey before (0h) and after (4h) co-culture with indicated V. alginolyticus attacker strains or alone. Co-cultures were incubated for 4 hours on (A) LB or (B) MLB agar plates at 30°C or 37°C. None = medium only. WT = wild-type.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4549250&req=5

ppat.1005128.g001: Antibacterial activities of V. alginolyticus T6SSs are differentially regulated by salinity and temperature.Viability of E. coli prey before (0h) and after (4h) co-culture with indicated V. alginolyticus attacker strains or alone. Co-cultures were incubated for 4 hours on (A) LB or (B) MLB agar plates at 30°C or 37°C. None = medium only. WT = wild-type.
Mentions: We previously reported that VaT6SS1 mediates bacterial killing on LB agar plates at 30°C [16]. As V. alginolyticus is a marine bacterium that thrives during warm months under various conditions in the environment and the host [22,28], we set out to determine how environmental conditions such as salinity and temperature affect the activity of VaT6SS1. To this end, we monitored the viability of E. coli before and after co-culture with wild-type V. alginolyticus, a Δhcp1 derivative in which VaT6SS1 is inactive, or alone on LB or MLB plates (containing 1% and 3% NaCl, respectively), at 30°C or 37°C. When co-cultured at 37°C, V. alginolyticus was unable to kill E. coli on LB plates (Fig 1A), but it was able to kill E. coli on MLB plates (Fig 1B). Surprisingly, whereas deletion of hcp1 largely abrogated the antibacterial toxicity of V. alginolyticus on LB at 30°C, it had only a marginal effect when co-cultures were grown on MLB plates at 30°C (Fig 1). This result suggested that there is another antibacterial determinant other than VaT6SS1 that can mediate interbacterial competition under high salt conditions.

Bottom Line: Using comparative proteomics and genetics, we identified their effector repertoires.We also showed that the T6SS2 secretes at least three antibacterial effectors.We demonstrated that a MIX V-effector from V. alginolyticus is a functional T6SS effector when ectopically expressed in another Vibrio species.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Biology, 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.

No MeSH data available.


Related in: MedlinePlus