The Pseudomonas aeruginosa Tse4 toxin assembles ion-selective and voltage-sensitive ion channels to couple membrane depolarisation with K+ efflux

Pseudomonas aeruginosa employs the Type VI secretion system (T6SS) to outcompete other bacteria in its environment. Among the effectors secreted by the T6SS of P. aeruginosa PAO1, Tse4 is known for its potent antibacterial activity. This study elucidates the molecular function of Tse4, which promotes cell depolarisation in competing bacteria. Our results show that Tse4 spontaneously incorporates into lipid monolayers and forms multiionic channels in planar bilayers, with either ohmic conduction or diode-like rectifying currents and a preference for cations over anions. These observations allow us to propose a model of action whereby Tse4 channels couple cell depolarisation with K+ efflux. These insights into Tse4s pore-forming activity enhance our understanding of bacterial competition and exemplify a finely tuned antibacterial strategy, coupling its ability to cause membrane depolarisation with potassium efflux that synergises with other T6SS effectors. These results highlight the sophistication of Pseudomonas aeruginosas competitive arsenal.