The Translocation and Assembly Module (TAM) ofEdwardsiella tardaIs Essential for Stress Resistance and Host Infection

Translocation and assembly module (TAM) is a protein channel known to mediate the secretion of virulence factors during pathogen infection.Edwardsiella tardais a Gram-negative bacterium that is pathogenic to a wide range of farmed fish and other hosts including humans. In this study, we examined the function of the two components of the TAM, TamA and TamB, ofE. tarda(namedtamA(Et)andtamB(Et), respectively). TamA(Et)was found to localize on the surface ofE. tardaand be recognizable by TamA(Et)antibody. Compared to the wild type, thetamAandtamBknockouts, TX01 Delta tamAand TX01 Delta tamB, respectively, were significantly reduced in motility, flagella formation, invasion into host cells, intracellular replication, dissemination in host tissues, and inducing host mortality. The lost virulence capacities of TX01 Delta tamAand TX01 Delta tamBwere restored by complementation with thetamA(Et)andtamB(Et)genes, respectively. Furthermore, TX01 Delta tamAand TX01 Delta tamBwere significantly impaired in the ability to survive under low pH and oxidizing conditions, and were unable to maintain their internal pH balance and cellular structures in acidic environments, which led to increased susceptibility to lysozyme destruction. Taken together, these results indicate that TamA(Et)and TamB(Et)are essential for the virulence ofE. tardaand required forE. tardato survive under stress conditions.