A mutualistic model bacterium is lethal to non-symbiotic hosts via the type VI secretion system

Area of Science:

• Microbiology
• Symbiosis Research
• Pathogen Discovery

Background:

• Bacteria are often classified as pathogenic or non-pathogenic, but this binary view is an oversimplification.
• Vibrio fischeri is an exclusive mutualistic symbiont of Hawaiian bobtail squid, yet employs molecules and behaviors typically associated with pathogenicity.
• Understanding how V. fischeri establishes beneficial symbiosis while exhibiting potentially harmful traits is crucial.

Purpose of the Study:

• To investigate the pathogenic potential of Vibrio fischeri towards non-symbiotic hosts.
• To determine if V. fischeri can induce disease phenotypes and mortality in aquatic organisms.
• To elucidate the role of the type VI secretion system 1 (T6SS1) in V. fischeri's interactions with eukaryotic cells.

Main Methods:

• Exposure of zebrafish embryos and Artemia nauplii to V. fischeri.
• Observation of mortality, growth delays, and disease phenotypes in exposed organisms.
• Genetic analysis to assess the role of the type VI secretion system 1 (T6SS1) in observed effects.

Main Results:

• Vibrio fischeri induced significant mortality in zebrafish embryos and Artemia nauplii.
• Non-lethal V. fischeri doses resulted in zebrafish growth delays and disease-indicative phenotypes.
• The conserved type VI secretion system 1 (T6SS1) on chromosome I was implicated in V. fischeri-induced mortality.

Conclusions:

• Vibrio fischeri demonstrates pathogenic capabilities, causing harm to aquatic organisms outside of its symbiotic context.
• The type VI secretion system 1 (T6SS1) of V. fischeri plays a role in its interactions with and potential harm to eukaryotic cells.
• This study challenges the traditional view of V. fischeri as solely a beneficial symbiont, revealing its capacity for pathogenicity towards non-symbiotic hosts.