Generation of Edwardsiella tarda ghosts by bacteriophage PhiX174 lysis gene E

Bacterial ghosts generated by the controlled expression of the PhiX174 lysis gene E in Gram-negative bacteria have been known to retain the functional and antigenic determinants of the envelope with their living counterparts and thus represent ideal vaccine candidates. The objective of this study was to examine the potential utility of the PhiX174 E gene driven by the PR/cI regulatory system for the generation of Edwardsiella tarda ghosts. The lysis kinetics in E. tarda were also compared with those in Escherichia coli. Generation of ghosts in the transformants of E. coli and E. tarda carrying plasmid pλPR-cI-Elysis was performed successfully by increasing the incubation temperature up to 42 °C. Compared to E. coli, in which lysis was observed within 30 min and was completed 2 h after induction of E gene expression, onset of E. tarda lysis occurred 2 h after temperature elevation and the lysis process was completed 16 h after induction. At the end of the lysis process, the efficiency of ghost induction in non-lyophilized E. tarda was 99.99 ± 0.01%, as the results of 10 replicate experiments showed. However, no bacterial growth was detected in lyophilized E. tarda. Holes ranging from 80 to 400 nm in diameter were observed in E. tarda ghosts by scanning electron microscopy. The present advance, especially regarding the tight control of 'E-lysis' and complete cell killing activity, will provide a new opportunity to improve the efficiency of vaccination against edwardsiellosis.