No abstract

In a previous investigation of bifidobacteria isolated from human dental caries (V. Scardovi and F. Crociani, Int. J. Syst. Bacteriol. 24:6-20, 1974), 40 strains were assigned to the new species Bifidobacterium dentiurn. In this study we examined 70 new strains of bifidobacteria isolated from dental caries. The morphological characteristics, biochemical reactions, fermentation patterns, end products from glucose metabolism, protein electrophoretic patterns, levels of DNA hybridization, and DNA G+C contents of these organisms revealed that they belong to three different taxa. One of these taxa was identified as B. dentium. The other two are described as the following new Bifidobacterium species in this paper: Bijidobacterium inopinaturn (type strain, DSM 10107) and Bijidobacterium denticolens (type strain, DSM 10105). The two new species differ from other Bijidobacterium species in their morphological characteristics (especially B. inopinatum, with its very small coccoid cells), in their carbohydrate fermentation patterns (most strains ferment dextran, and B. inopinatum does not ferment galactose), and in their DNA base compositions (especially B. inopinatum).

Genetic relatedness among 179 strains representing 13 named species and several unnamed taxa of the genus Bifidobacterium from three main habitats, i.e., (i) feces of man, (ii) feces of various other animals, and (iii) the bovine rumen, was assessed by means of deoxyribonucleic acid (DNA)-DNA hybridization by using a filter-paper technique in competition experiments. Assignment of these strains to the genus Bifidobacterium was based on the production of lactic and acetic acids as chief products from glucose, lack of gas production, fructose-6-phosphate phosphoketolase activity, and on morphology. About 180 DNA competitors were tested with 23 reference systems. Several genetically distinct groups were recognized. Little or no DNA homology was demonstrated between some of the groups, suggesting large evolutionary divergence in this genus. B. infantis, B. liberorum, and B. lactentis form one of these groups; the ecological significance of this relatedness was discussed. The DNA of the following pairs are homologous: (i) B. breve and B. parvulorum, (ii) B. thermophilum and B. ruminale, and (iii) B. pseudolongum and B. globosum. Within a number of strains assigned to B. adolescentis, many of which were isolated from waste waters, a large genetic heterogeneity was demonstrated: in addition t o B. adolescentis, at least three unrelated groups were recognized and are provisionally referred to as "dentium, " "catenulatum, " and "angulatum. " Since these groups are not related genetically to any species of the genus and are phenotypically distinct, they may represent new species. The validity of the species B. bifidum, B. longum, and B. suis was confirmed at the genetic level.

Previous studies by us and our colleagues suggested three distinctive deoxyribonucleic acid (DNA) homology groups among the bifidobacteria; these were provisionally named "catenulatum ," "dentium ," and "angulatum ." One hundred eighty-four strains isolated from sewage, in addition to many of the strains from the previous study, were investigated and their DNA homology relationships were assessed using 23 reference systems. Strains in the catenulatum group were found not to differ significantly from those of Bifidobacterium adolescentis Reuter in their main physiological characters, such as sugars fermented and temperature, pH, and oxygen relationships; however, their DNA reciprocal homology is only some 50%, their guanine plus cytosine values were 54.7 * 0.2 and 59.4 * 0.4 mol %, respectively, and there were some morphological differences between them. The DNA of the dentium group has only about 45% homology with the DNA of B. adolescentis and is even less related to other members of the genus. The dentium strains can also be distinguished from other bifidobacteria by means of their sugar fermentations. The DNA of the angulatum group has little or no homology with that of any other bifidobacteria; the angulatum group also has a distinctive pattern of sugar fermentation and a unique morphology, resembling that of the coryneform bacteria. The three groups are named and described as new species of the genus Bifidobacterium: B. catenulatum, B. dentium, and B. angulatum. The type strains of these species are B669 (= ATCC 27539), B764 (= ATCC 27534), and B677 (= ATCC 27535), respectively. DNA-DNA homology relationships are basic to currently proposed species concepts, and data are presented confirming the reliability of critical experimental parameters influencing filter-bound DNA and thus the final relative homology values (e.g., temperature and time of incubation and annealing of DNA in the presence of homologous and heterologous competitive or nonspecific DNA, and the replicability of homology values using different homologous DNA preparations with single DNA competitor and reference DNA).In a previous investigation (32), a large old cultures. However, only seven strains of B. number of bifidobacteria displaying the general fermentation pattern of Bifidobacterium adolescentis Reuter were differentiated by means of deoxyribonucleic acid (DNA)-DNA hybridization into three groups, which were named "catenulatum, " "den tium," and 'hngulatum. " The angulatum group was well characterized by an unusual and constant "V" or angular cell disposition, suggesting the "snapping" type of cell division of the corynebacteria. The other two groups could not easily be distinguished phenotypically from B. adolescentis, although strains in the group named catenulatum commonly produced cells in chains, especially in adolescentis from Reuter's collection and another strain isolated by us from adult feces were available for study, and on the basis of DNA homology relatedness we could assign only 10 strains to the catenulatum group. Th...

Page 10, column 1, paragraph 4, line 5 : Change "(0.1 N, pH 7)" t o read "(0.1 M, pH 7)." Page 18, column 2, paragraph 9, lines 2 and 3: Change "maximum, 42 to 42 C" t o read Page 19, column 1, paragraph 3, line 2: Change "(some 30%)" t o read "(some 20%)." Paragraph a, line 2: Change "counts per min per g" to read "counts per min per yg." "maximum, 42 to 43 C." 10, line 2: Change "maximum, 42 t o 42 C" t o read "maximum, 42 to 43 C.