Flavobacterium tructae sp. nov. and Flavobacterium piscis sp. nov., isolated from farmed rainbow trout (Oncorhynchus mykiss)

Abstract

Four Gram-staining-negative, catalase- and oxidase-positive, pale-orange pigmented bacterial strains (435-08(T), 47B-3-09, 412R-09(T) and 60B-3-09) were isolated from diseased rainbow trout. Analysis of their 16S rRNA gene sequences suggested their adscription to the genus Flavobacterium. Strains formed two phylogenetic groups represented by strains 435-08(T) and 47B-3-09 (group A), and strains 412R-09(T) and 60B-3-09 (group B) displaying 16S rRNA sequence similarities greater than 99.8-99.9% within their respective groups. Strain 435-08(T) exhibited the highest levels of similarity with Flavobacterium aquidurense WB-1.1.56(T) (98.6% sequence similarity) and strain 412R-09(T) with Flavobacterium frigidimaris KUC-1(T) and Flavobacterium aquidurense WB-1.1.56(T) (98.9% and 98.6% sequence similarity, respectively). DNA-DNA hybridization studies showed low levels of relatedness between strain 435-08(T) and strain 412R-09(T) and between both strains and the most closely related species of the genus Flavobacterium. The genomic DNA G+C contents of strains 435-08(T) and 412R-09(T) were 36.2 and 34.3 mol%, respectively. The predominant respiratory quinone of both strains was MK-6 and the major fatty acids were iso-C(15 : 0), C(16 : 1)ω7c and C(15 : 0). The two groups of strains could be distinguished from each other and from related species of the genus Flavobacterium by a number of phenotypic properties. Phylogenetic, genotypic and phenotypic evidence indicated that strains of groups A and B represent two novel species of the genus Flavobacterium, for which the names Flavobacterium tructae sp. nov. (type strain 435-08(T) = CECT 7791(T) = CCUG 60100(T)) and Flavobacterium piscis sp. nov. (type strain 412R-09(T) = CECT 7911(T) = CCUG 60099(T)) are proposed.