Abstract
The eth hemolysin gene locus of Edwardsiella tarda encodes the hemolysin EthA protein and its accessory protein EthB. We constructed mutants by site directed marker insertion mutagenesis in ethA or ethB by a method employing the integration of a mobilizable suicide plasmid containing a portion of the ethA or ethB coding sequence into the chromosome. Both the ethA- and ethB-matants lacked extracellular, cell-associated, and intracellular hemolytic activities. These results indicate that the EthB protein is essential for the hemolytic activity of EthA. The EthA protein may be activated in the periplasmic region of the cell by the EthB protein which is located on the outer membrane of the cell. The loss of hemolytic activity of the ethA- and ethB-deficient mutants suggests that E. tarda has only one hemolysin gene locus in the genome.
