Tit-for-tat: type VI secretion system counterattack during bacterial cell-cell interactions

Area of Science:

• Microbiology
• Bacterial cell-cell interactions
• Protein secretion systems

Background:

• The bacterial type VI secretion system (T6SS) is a complex machine for delivering effector proteins into target cells.
• Dynamic interactions between T6SS organelles in adjacent Pseudomonas aeruginosa cells, termed "T6SS dueling," have been observed.
• T6SS dueling is hypothesized to be a mechanism for bacterial attack and defense.

Purpose of the Study:

• To investigate the influence of T6SS dueling on the predation of heterologous bacterial species by P. aeruginosa.
• To determine if prey T6SS activity affects the efficacy of P. aeruginosa T6SS-mediated killing.
• To elucidate the regulatory signals governing T6SS organelle assembly and counterattack.

Main Methods:

• Time-lapse fluorescence microscopy to observe T6SS dynamics in P. aeruginosa.
• Co-culture experiments with P. aeruginosa and prey species (Vibrio cholerae, Acinetobacter baylyi).
• Assays to quantify bacterial killing and T6SS activity in interacting populations.

Main Results:

• T6SS dueling significantly enhances the ability of P. aeruginosa to prey on other bacterial species.
• The killing of V. cholerae and A. baylyi by P. aeruginosa T6SS is strongly stimulated by the presence of T6SS activity in the prey.
• A signaling mechanism appears to regulate P. aeruginosa T6SS assembly and lethal counterattack in response to direct T6SS attack.

Conclusions:

• T6SS dueling is a critical factor in bacterial interspecies competition and predation.
• The efficacy of bacterial T6SS attacks is modulated by the defensive capabilities of the prey.
• A novel signaling pathway links T6SS attack detection to the activation of T6SS-mediated counteroffensives.