The family cytophagaceae

Abstract

The family Cytophagaceae, which spans at least 25 genera and 80 species, is one of the largest families in the phylum Bacteroidetes. The members of the family are diverse in terms of physiology and habitat, but some common properties can be identified. Members of the family Cytophagaceae are commonly isolated from marine, freshwater, and terrestrial habitats. All known members are heterotrophic and most are aerobic with primarily respiratory metabolism. Menaquinones of type 7 (MK7) are the major respiratory quinones, a feature that they share with other members of the class Cytophagia but that distinguishes them from physiologically similar bacteria from the family Flavobacteriaceae, which have menaquinones of type 6 (MK6). Most species have rod-shaped cells, with some exhibiting filamentation and others forming curved, spiral, or ring-shaped cells. Most species are pigmented yellow, orange, red, or pink as a result of flexirubin pigments, carotenoids, or both. Movement over surfaces by gliding motility is common but not universal, whereas other forms of motility have apparently not been observed. Most species are mesophilic, but a few are psychrophilic. Many members of the family digest macromolecules such as polysaccharides or proteins. Members of the type genus, Cytophaga, are proficient at digestion of insoluble cellulose, as are members of the closely related genus Sporocytophaga. Cellulose utilization by members of the genus Cytophaga appears to involve an apparently novel collection of glycosyl hydrolases. Obvious cellobiohydrolases that are often associated with cellulose utilization by other bacteria are lacking. Cellulose utilization may involve novel cell-surface machinery for initial digestion of cellulose and for uptake of the resulting cellodextrins across the outer membrane. Other noteworthy members of the family include gliding bacteria of the genera Flexibacter and Microscilla, spiral and curved bacteria of the genera Arcicella, Flectobacillus, Larkinella, Runella, and Spirosoma, desiccation and radiation resistant members of the genus Hymenobacter, and strongly adherent bacteria of the genus Adhaeribacter. Phylogenetic analyses based on 16S rRNA sequences revealed multiple potential problems with the family as currently described. The family Cytophagaceae appears to encompass two divergent clades of bacteria that are not well resolved from members of the families Cyclobacteriaceae and Flammeovirgaceae. A restructuring of the family Cytophagaceae may be necessary, either splitting it into two or more families or combining it with the families Cyclobacteriaceae and Flammeovirgaceae.