Cutting a Gordian Knot: Emended Classification and Description of the Genus Flavobacterium, Emended Description of the Family Flavobacteriaceae, and Proposal of Flavobacterium hydatis nom. nov. (Basonym, Cytophaga aquatilis Strohl and Tait 1978)

The phylogenetic positions and G+C contents of most species belonging to the genera Flavobacterium, Cytophaga, and Flexibacter and several related taxa were determined. Most of the strains included in this study belong to rRNA superfamily V, as shown by DNA-rRNA hybridization data, but the three main genera are highly polyphyletic. Several so-called Cytophaga and Flexibacter species isolated from soil and freshwater cluster with the type species of the genus Flavobacterium, Flavobacterium aquatile, and with Flavobacterium branchiophilum. The fatty acid and protein profiles of members of this group of organisms were determined. We provide an emended description of the genus Flavobacterium and propose new combinations for the following 7 of the 10 validly described species included in this genus: Flavobacterium columnare, Flavobacterium flevense, Flavobacterium johnsoniae (we also correct the specific epithet of this taxon), Flavobacterium pectinovarum, Flavobacterium psychrophilum, Flavobacterium saccharophilum, and Flavobacterium succinicans. A new name, Flavobacterium hydatis, is proposed for [Cytophaga] aquatilis Strohl and Tait 1978. The emended genus Flavobacterium contains bacteria that have the following main characteristics: gram-negative rods that are motile by gliding, produce yellow colonies on agar, are chemoorganotrophs and aerobes, decompose several polysaccharides but not cellulose, and are widely distributed in soil and freshwater habitats. Three Flavobacterium species are pathogenic for fish. The G+C contents of Flavobacterium DNAs range from 32 to 37 mol%. An emended description of the family Flavobacteriaceae is also provided.