Insight into the resilience and susceptibility of marine bacteria to T6SS attack by Vibrio cholerae and Vibrio coralliilyticus.

Ryan Guillemette,Blake Ushijima,Claudia C Häse,Mihika Jalan,Farooq Azam,Surajit Das

doi:10.1371/journal.pone.0227864

Ryan Guillemette, Blake Ushijima + Show 4 more

Open Access

https://doi.org/10.1371/journal.pone.0227864

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Abstract

The type VI secretion system (T6SS) is a nanomachine capable of killing adjacent microbial cells in a contact-dependent manner. Due to limited studies, relatively little is known about the range of marine bacteria that are susceptible to T6SS attack. Here, 15 diverse marine bacterial isolates from the phyla Bacteroidetes and Ɣ-Proteobacteria were challenged against the marine bacterium and human pathogen, Vibrio cholerae, which has a well described T6SS. V. cholerae killed several of the tested Ɣ-Proteobacteria, including members of the orders Vibrionales, Alteromonadales, Oceanospirillales, and Pseudomonadales. In contrast, V. cholerae co-existed with multiple Bacteroidetes and Ɣ-Proteobacteria isolates, but was killed by Vibrio coralliilyticus. Follow-up experiments revealed that five V. coralliilyticus strains, including known coral and shellfish pathogens survived the T6SS challenge and killed V. cholerae. By using predicted protein comparisons and mutagenesis, we conclude that V. coralliilyticus protected itself in the challenge by using its own T6SS to kill V. cholerae. This study provides valuable insight into the resilience and susceptibility of marine bacteria to the V. cholerae T6SS, and provides the first evidence for a functional T6SS in V. coralliilyticus, both of which have implications for human and ocean health.

Highlights

Bacterial-bacterial antagonism plays a major role in shaping bacterial community structure and function [1,2,3,4,5]
We considered that further exploration into the range of marine bacteria that are susceptible to the T6SS should increase our understanding of the types of bacteria that a specific T6SS can kill, while helping to inform microbial ecologists on select types of bacteria, and the mechanisms, that provide resistance to T6SS attack
To test the efficacy of V. cholerae T6SS deployment against marine bacteria, we challenged a suite of marine isolates from different environmental and phylogenetic backgrounds (Table 2) against V. cholerae with an active T6SS (T6SS+), or its isogenic T6SS knockout mutant (T6SS-) derivative that was created and confirmed in a previous study

Summary

Introduction

Bacterial-bacterial antagonism plays a major role in shaping bacterial community structure and function [1,2,3,4,5]. Studies investigating marine bacterial-bacterial antagonism predominantly focused on the production and release of antibiotics by predatory bacteria as a means to inhibit their preys’ growth [6,7,8] While these findings demonstrated that select marine bacteria were capable of killing other bacteria, it has been suggested that the relatively low frequency of killing that was observed may have been due to the common use of non-marine. Experiments that used more ecologically relevant model prey (e.g. isolates from pelagic seawater, marine particles, and coral) found that killing occurred in > 50% of the competition assays [9, 10] These studies showed that some of the model prey were able to survive the challenge against select predatory bacteria that had killed other bacteria, suggesting that those surviving prey possessed defense mechanisms [9, 10]

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