The phospholipase effector Tle1 Vc 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 anti-prokaryotic 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 Tle1 Vc , a phospholipase effector in atypical pathogenic V. cholerae E1 that is secreted by T6SS via its interaction with VgrG1 E1 . Tle1 Vc 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 Tle1 Vc possessed phospholipase A 1 activity and phospholipase A 2 activity, and that Tle1 Vc -induced toxicity required a serine residue (S356) and two aspartic acid residues (D417 and D496). Cells intoxication with Tle1 Vc lead to membrane depolarization and alter membrane permeability. Tli1 tox- , a cognate immunity protein, directly interacts with Tle1 Vc to neutralize its toxicity. Moreover, Tle1 Vc can kill multiple microorganisms by T6SS and promote in vivo fitness of V. cholerae through mediating antibacterial activity. Tle1 Vc 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 Tle1 Vc -mediated strong TFT response, maximizing effector functions. Overall, our study characterized the antibacterial mechanism of phospholipase effector Tle1 Vc and its multiple physiological significance.