Use of Bacillus strains to assay diarrhetic and paralytic shellfish toxins in scallops, Patinopecten yessoensis

Two bacterial strains the growth of which was inhibited by extracts of the hepatopancreas of scallops, Patinopecten yessoensis, were isolated from soil and identified as being Bacillus spp. The growth of both strains was inhibited by the addition of okadaic acid or saxitoxin to the medium. The growth of Bacillus OH-D decreased to 30% with 10 microgram of okadaic acid per 10 ml of broth, and was inhibited completely with 25 microgram of this acid per 10 ml of the broth. There were clear growth-inhibition zones around cylinders containing saxitoxin on a carpet of Bacillus OH-P with the width of the zone proportional to the concentration of saxitoxin. Crude and partially purified fractions of hepatopancreas containing diarrhetic or paralytic shellfish toxins inhibited the growth of strains OH-D or OH-P, respectively. Free fatty acids in the hepatopancreas did not interfere with the inhibition of growth by these toxins. Our findings suggested microbial titration could be used to assay shellfish toxins instead of assays of lethality in mice