Ichthyobacterium seriolicida gen. nov., sp nov., a member of the phylum 'Bacteroidetes', isolated from yellowtail fish (Seriola quinqueradiata) affected by bacterial haemolytic jaundice, and proposal of a new family, Ichthyobacteriaceae fam. nov.

A novel Gram-stain-negative, rod-shaped (0.3 x 4-6 mu m), non-flagellated, aerobic strain with gliding motility, designated JBKA-6(T), was isolated in 1991 from a yellowtail fish, Seriola quinqueradiata, showing symptoms of bacterial haemolytic jaundice. 16S rRNA gene sequence analysis showed that strain JBKA-6(T) was related most closely to members of the family Flavobacteriaceae in the phylum 'Bacteroidetes'. Furthermore, based on gyrB gene sequence analysis, JBKA-6(T) was classified into a single clade within the order Flavobacteriales, which was distinct from the known clades of the families Flavobacteriaceae, Blattabacteriaceae and Cryomorphaceae. The predominant isoprenoid quinone was identified as MK-6 (97.9 %), and the major cellular fatty acids (>10 %) were C-14 : 0 and iso-C-15 : 0. The main polar lipids were phosphatidylethanolamine, three unidentified phospholipids, two unidentified aminophospholipids and two unidentified polar lipids. The DNA G + C content of JBKA-6(T), as derived from its whole genome, was 33.4 mol%. The distinct phylogenetic position and phenotypic traits of strain JBKA-6(T) distinguish it from all other described species of the phylum 'Bacteroidetes', and therefore it was concluded that strain JBKA-6(T) represents a new member of the phylum 'Bacteroidetes', and the name Ichthyobacterium seriolicida gen. nov., sp. nov. is proposed. The type strain of Ichthyobacterium seriolicida is JBKA-6(T) (=ATCC BAA-2465(T)=JCM 18228(T)). We also propose that Icthyobacterium gen. nov. is the type genus of a novel family, Ichthyobacteriaceae fam. nov.