Studies on the Taxonomy of Causative Organisms of Fish Vibriosis

Molecular biological classification of representative strains

Abstract

The ratio of GC composition and DNA-DNA homology among the representative strains of each phenon and between the five phenons and six single member-clusters, as described in a previous report (TAJIMA et al., 1985b), were examined. All of the strains tested exhibited GC values in a range from 43 to 46 %. From these results, the strains used were reconfirmed as Vibrio. The DNA of reference strains (phenon I: V-7 NCMB 6, V-116 NCMB 407, phenon II: V-105 NOAA V-1669) of phenon I (V. anguillarum) and phenon II (Vibrio sp.) were genetically homologous with isolates belonging to the corresponding phenons, while they were very distantly related to the isolates belonging to phenons III, IV, V and other single member-clusters. A homology of 77-80% of DNA for phenon II isolates against the reference DNA (V-7 NCMB 6) of phenon I was comparable to that of DNA for phenon I isolates. According to the numerical taxonomy carried out previously, we considered phenon I and phenon II to be different species due to similarities of less than 57 %, but the present results of the DNA-DNA homology indicated that these two phenons probably belong to the same species.