Chemical and electroporated transformation of Edwardsiella ictaluri using three different plasmids


  • Editor: Craig Shoemaker

Correspondence: Riccardo Russo, United States Department of Agriculture, Agricultural Research Service, Aquatic Animal Health Research Unit, 990 Wire Road, Auburn, AL 36832, USA. Tel.: +1 334 887 3741; fax: +1 334 887 2983; e-mail:


Transfer of DNA by conjugation has been the method generally used for genetic manipulation of Edwardsiella ictaluri because, previously, attempts to transform E. ictaluri by the uptake of naked DNA have apparently failed. We report here the successful transformation of seven strains of E. ictaluri using electroporation and two different chemical procedures [conventional calcium chloride (CaCl2) and ‘one-step’ (polyethylene glycol, dimethyl sulfoxide and MgSO4) protocols]. Seven strains of E. ictaluri were transformed using three different plasmids [pZsGreen, pUC18 and pET-30a(+)]. The highest transformation efficiency was achieved by electroporation (5.5±0.2 × 104 transformants ng−1 plasmid DNA) than with the CaCl2 (8.1±6.1 × 10−1 transformants ng−1 plasmid) and the ‘one-step transformation’ protocol (2.5±2.7 transformants ng−1 plasmid). An efficient transformation by electroporation required only 0.2 ng of plasmid compared with 200 ng required for the CaCl2 and one-step protocols. The plasmids were stably maintained in E. ictaluri grown in the presence of antibiotic for 12 or more passages. The results of this study show that transformation of E. ictaluri by electroporation can be routinely used for the molecular genetic manipulation of this organism, and is a quicker and easier method than transformation performed by conjugation.