Abstract
Eight unidentified fish pathogens and 10 strains received as "Flexibacter columnaris," Cytophaga psychrophila," and Flexibacter maritimus were compared with the type strains of all previously described species in the genera Cytophaga and Flexibacter and with seven Flavobacterium species by determining levels of deoxyribonucleic acid (DNA) relatedness (S1 nuclease method) and by performing phenotypic tests. The name Flexibacter columnaris sp. nov. is revived for a DNA relatedness group comprising eight strains that are 75 to 100% related to strain TG 39/87 and 0 to 8% related to all of the other species studied. These strains produce flat rhizoid colonies which adhere to agar, show strong gliding movement, absorb Congo red, reduce nitrate to nitrite, and produce H2S. The guanine-plus-cytosine content of the DNA is 32 mol%. The type strain is strain NCMB 2248 (= ATCC 23463). The name Flexibacter psychrophilus sp. nov. is revived for a DNA relatedness group comprising seven strains that are 90 to 100% related to strain NCMB 1947T (T = type strain) and 0 to 5% related to all of the other species studied. These strains produce circular, convex colonies that have regular or spreading margins and do not adhere to agar, show very slow gliding movement, do not absorb Congo red, do not reduce nitrate, and do not produce H2S. The guanine-plus-cytosine content of the DNA is 33 mol%. The type strain is strain NCMB 1947. Both F. columnaris and F. psychrophilus produce the flexirubin type of pigments, are strongly proteolytic, and do not hydrolyze (or produce acid from) any carbohydrate. Flexibacter maritimus (three strains) was shown to constitute a DNA relatedness group that is 0 to 8% related to all of the other species tested. Furthermore, this organism can be differentiated by phenotypic tests. The presence of F. maritimus in Europe is shown for the first time.

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