The phospholipase effector Tle1Vc promotes Vibrio cholerae virulence by killing competitors and impacting gene expression

Vibrio cholerae utilizes the Type VI secretion system (T6SS) to gain an advantage in interbacterial competition by delivering antiprokaryotic effectors in a contact-dependent manner. However, the impact of T6SS and its secreted effectors on physiological behavior remains poorly understood. In this study, we present Tle1Vc, a lipase effector in atypical pathogenic V. cholerae E1 that is secreted by T6SS via its interaction with VgrG1E1. Tle1Vc contains a DUF2235 domain and belongs to the Tle1 (type VI lipase effector) family. Bacterial toxicity assays, lipase activity assays, and site-directed mutagenesis revealed that Tle1Vc-induced toxicity required two aspartic acid residues (D417 and D496) and a serine residue (S356). Cell intoxication with Tle1Vc leads to membrane depolarization and altered membrane permeability. Tli1tox-, a cognate immunity protein, directly interacts with Tle1Vc to neutralize its toxicity. Moreover, Tle1Vc can kill multiple microorganisms and promote in vivo fitness of V. cholerae. Tle1Vc induces bacterial motility by increasing the expression of flagellar-related genes independently of functional T6SS and the tit-for-tat (TFT) response, where Pseudomonas aeruginosa uses its T6SS-H1 cluster to counterattack other offensive attackers. Our study also demonstrated that the physical puncture of E1 T6SS can induce a moderate TFT response, which is essential to the Tle1Vc-mediated strong TFT response, maximizing effector functions. Overall, our study characterized the Tle1Vc lipase effector and its physiological significance.