Taxonomical re-examination of two pathogenic Vibrio species isolated from milkfish and swimming crab

Abstract

A taxonomical re-examination of two pathogenic bacteria belonging to the genus Vibrio, one from an eye disease of milkfish (Chanos chanos) in the Philippines and the other from vibriosis of larval swimming crab (Portunus trituberculatus) in Japan, was made by examining their phenotypic features and measuring DNA-DNA relatedness. As a result, the bacterium from milkfish was identified as V. harveyi based on the high DNA homology value of above 84% between the two milkfish isolates and the type strain of V. harveyi and coincidence in phenotypic characteristics. Strain 85Z-1, the representative strain of the causative bacterium (Vibrio sp. Zoea) of vibriosis in swimming crab, showed higher DNA relatedness than 75% to other 3 strains of Vibrio sp. Zoea, about 50% relatedness to strains of V. harveyi, and lower relatedness than 46% to the other species examined. These results indicate that Vibrio sp. Zoea is a new genomic species most closely to V. harveyi. However, it is difficult to distinguish phenotypically Vibrio sp. Zoea from V. harveyi isolated from milkfish, thus species name for Vibrio sp. Zoea could not be proposed.