ABSTRACT
The genus Cryptobacterium was proposed by Nakazawa et al. in 1999 for strains of asaccharolytic, anaerobic, short gram-positive rods.1 Initially, these strains were isolated from human oral cavities as Eubacterium-like organisms. The genus Eubacterium has been deŠned mainly on the basis of negative metabolic characteristics.2 Because of its broad deŠ- nition, a large number of novel gram-positive rods isolated from oral cavities have been classiŠed previously as members of the genus Eubacterium. Therefore, it is inevitable that considerable heterogeneity exists among the species within the genus. In fact, it is described that the genus Eubacterium contains many gram-positive rods that are phylogenetically unrelated, and some of which qualify as members of the genus Eubacterium but could not be assigned to any of the named species.2-8 In addition, several novel genera have been proposed for some of asaccharolytic, anaerobic, short grampositive rods (e.g., Cryptobacterium, Slackia, Eggerthella, and Mogibacterium), and some species of Eubacterium have been transferred to the novel genera according to their phylogenetic characteristics.1,9,10
Cryptobacterium curturn is the sole species in the genus Cryptobacterium on the basis of morphological and biochemical characteristics, SDS-PAGE of whole-cell protein and Western immunoblotting analysis, G + C content, DNA-DNA hybridization, and 16S rRNA gene sequence data as member of the family Coriobacteriaceae.1 To date, the family Coriobacteriaceae is deŠned only in terms of the 16S rRNA gene signature nucleotide, just like the subclass Coriobacteridae and the order Coriobacteriales.11 Indeed, it would seem appropriate to
examine the value of chemotaxonomy in improving the deŠnition of the order and family. At the time of writing, the family Coriobacteriaceae proposed by Stackebrandt et al. comprises the following 13 genera: Adlercreutzia, Asaccharobacter, Atopobium, Collinsella, Coriobacterium, Cryptobacterium, Denitrobacterium, Eggerthella, Enterorhabdus, Gordonibacter, Olsenella, Paraeggerthella, and Slackia.1,10,12-23
Cryptobacterium cells are very short (0.4 × 0.8-1.0 μm), obligate anaerobic, nonmotile, nonspore forming rods that occur singly or in masses. The growing cells are grampositive, but occasionally cells in older cultures are gramnegative. Transmission electron micrographs of thin sections of cell of C. curtum 12-3T (=ATCC 700863) showed a singlelayer cell wall approximately 10 nm in thickness (Figure 7.1), which is typical cell wall of gram-positive bacteria. Pili-or ³agella-like structures were not found. The scanning electron micrograph of C. curtum 12-3T, occurring in chains, is also available.24
