1.C.132. The TseL Toxin (TseL) Family
Comparison of multiple Vibrio cholerae strains indicated that effectors are encoded in T6SS effector modules on mobile genetic elements. Unterweger et al. 2015 identified a diverse group of chimeric T6SS adaptor proteins required for the translocation of diverse effectors encoded in modules. An example for a T6SS effector that requires T6SS adaptor protein 1 (Tap-1) is TseL found in pandemic V. cholerae O1 serogroup strains and other clinical isolates. Unterweger et al. 2015 proposed a model in which Tap-1 is required for loading TseL onto the secretion apparatus. After T6SS-mediated TseL export is completed, Tap-1 is retained in the bacterial cell to load other T6SS machines. It acts on prokaryotic as well as eukaryotic target cells (Miyata et al. 2013; Dong et al. 2013). The TseL activity is not required for T6SS activity (Liang et al. 2019). TseL, but no other effectors or physical puncture, triggers a tit-for-tat response of P. aeruginosa H1-T6SS. Although E. coli is sensitive to all periplasmically expressed effectors, P. aeruginosa is most sensitive to TseL alone. Kamal et al. 2020 identified a number of stress response pathways that confer protection against TseL.