Tke5 is a novel Pseudomonas putida toxin that depolarises membranes killing plant pathogens

The soil bacterium Pseudomonas putida injects toxic proteins into neighbouring competitors, including resilient phytopathogens, using the Type VI secretion system (T6SS). The secretion of toxins endows P. putida with a significant fitness advantage, allowing this biocontrol agent to thrive in plant-related polymicrobial environments and prevent phytopathogen infections. Despite its agricultural significance, the toxin repertoire of P. putida, particularly those secreted via the K2- and K3-T6SSs, remains poorly understood. We present the first comprehensive molecular study of Tke5, a potent toxin encoded within the K3-T6SS, which represents the first comprehensive functional analysis of the BTH_I2691 protein family. Our biophysical data demonstrate that Tke5 is a pore-forming toxin that disrupts bacterial membranes through selective ion transport, inducing membrane depolarisation and cell death. Unlike conventional detergent-like pore-forming toxins, Tke5 preserves overall membrane integrity, avoiding large, non-specific disruptions. This unique mechanism offers a powerful approach to targeting resilient phytopathogens. This study reveals a previously undescribed mode of action within a widespread yet understudied toxin family. Our findings highlight the potential of P. putida as a biocontrol agent, offering alternatives to chemical pesticides by exploiting novel toxin mechanisms. Understanding these bacterial toxins is crucial for developing effective strategies to combat plant pathogens.