Toxicity to bivalve hemocytes of pathogenic Vibrio cytoplasmic extract

Using a chemiluminescence (CL) test, it had been previously demonstrated th at Vibrio pectenicida, which is pathogenic to Pecten maximus larvae, was ab le to inhibit completely the CL activity of P, maximus hemocytes and partia lly inhibit those of Crassostrea gigas, Conversely, a Vibrio sp, strain, S3 22, pathogenic to C,gigas larvae was more active in reducing the CL activit y of oyster hemocytes than of scallop hemocytes, Using this same CL biotest , V, pectenicida and S322 cytoplasmic extracts were shown to reproduce CL i nhibition while the cytoplasmic extract of a nonpathogenic strain (U1, Pseu doalteromonas) was without effect. Moreover, cytoplasmic extract as well as live V, pectenicida cells provoked, within a few hours, death of P. maximu s hemocytes adhering to a glass slide. After partial purification, it was s hown that toxic activities of V. pectenicida cytoplasmic extract was due to a toxin, named VHKT (for vibrio hemocyte-killer toxin), which is heat stab le, acid and protease resistant, and less than 3 kDa in molecular weight. A ttempts to purify VHKT by reverse-phase (C18) HPLC separated activity into the fraction eluted by water at a retention time of 4.02 min. (C) 2001 Acad emic Press.