An accessory protein of the iron-regulated hemolysin of Edwardsiella tardais necessary for hemolytic activity

The eth hemolysin gene locus of Edwardsiella tarda encodes the hemolysin Et hA protein and its accessory protein EthB. We constructed mutants by site d irected marker insertion mutagenesis in ethA or ethB by a method employing the integration of a mobilizable suicide plasmid containing a portion of th e ethA or ethB coding sequence into the chromosome. Both the ethA- and ethB -mutants 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 pe riplasmic region of the cell by the EthB protein which is located on the ou ter membrane of the cell. The loss of hemolytic activity of the ethA- and e thB-deficient mutants suggests that E. tarda has only one hemolysin gene lo cus in the genome.