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.
Among the several thousand bifidobacteria of our collection, 244 strains from the feces of rabbits and suckling pigs, the rumen of cattle, the feces of breast-and bottle-fed infants, the feces of calves, and from sewage are recognized by means of deoxyribonucleic acid (DNA)-DNA hybridization (competition filter method) as belonging to four new, distinct DNA homology groups. Twenty reference DNA preparations from the type strains of the currently known species or from reference strains of the homology groups of Bifidobacterium were used for comparison. The phenotypic traits which distinguish these four groups from previously described species of the genus Bifidobacterium include gross morphology, fermentation characteristics, guanine plus cytosine content of the DNA, the interpeptide bridge of the cell-wall peptidoglycan, and the transaldolase and 6-phosphogluconate dehydrogenase isozyme pattern (by starch gel electrophoresis). The four groups are named and described as new species of the genus Bifido bacterium: B. cuniculi, B. choerinum, B. boum, and B. pseudocatenulatum. The type strains of these species are RA93 (=ATCC 27916), SU806 (=ATCC 27686), RU917 (=ATCC 27917), and B1279 (=ATCC 27919), respectively.Several species and provisional groups of bifidobacteria isolated from the feces of adult rabbits have been named and described (17,20,24). One of the provisional groups was referred to by Trovatelli et al. (24) as deoxyribonucleic acid (DNA) homology group 11. In the present study, this group of bifidobacteria, here referred to as the cuniculi DNA homology group, is described in detail and is recognized as a new species.Bifidobacteria from the feces of piglets were isolated and studied by Zani et al. (26). Most of the strains were identified on the basis of DNA homology relationships as members of Bifidobacterium suis, B. thermophilum, B. globosum, or B. pseudolongum. These authors also reported that 13 of 95 strains examined were distinct from previously described species. This group was designated homology group coirinense. A few fermentation characteristics and the DNA homology relationships to other organisms from this habitat were reported (26), but the taxonomic status of this group was not established. In the present work, this group, referred to here as the choerinum DNA homology group, is also described and recognized as a new species.The rumen is an important habitat of bifidobacteria, especially when the animals are fed carbohydrate-rich diets (25). Indeed, isolates from sheep rumen were used for our fmst studies on the fructose 6-phosphate shunt mechanism of glucose degradation by bifidobacteria (15). Species reported from this habitat include B. globosum and B. ruminale. B. ruminale was found to be identical with B. thermophilum, a species isolated by Mitsuoka (6) from the feces of swine. Other bifidobacteria from the rumen (strains RU276, RU348, and RU354) at first appeared to be variants of B. ruminale (ref. 18, p. 290 Table 10, p. 292). In recent investigations on the effect of diet on the ...
Summary. Ninety‐five strains of bifidobacteria isolated from 52 specimens of piglet faeces collected at 19 farms were studied. The main phenotypic characters of the strains were determined; however their assignment to known species of the genus Bifidobacterium was based primarily on their deoxyribonucleic acid homology relationships following DNA‐DNA hybridization tests. The majority of the strains were recognized as Bifidobacterium suis Matteuzzi et al. Some strains could not be assigned to any known species of the genus so they were allotted provisionally to 2 unassigned bacterial groups.
Among 130 strains of bifidobacteria isolated from the feces of rabbits, 26 were distinctive in: (i) having large cellular dimensions (4 to 5 by 17 t o 20 pm); (ii) requiring an initial pH of 5.3 to 5.5 for optimum growth; and (iii) having a need for Tween 80 for optimal development in Trypticase-phytone-yeast extract-glucose medium. The other characters of these 26 strains, such as their temperature and oxygen relationships, catalase production, nitrate reduction, end products from glucose fermentation, enzymes of the hexose catabolic pathway, the percent of guanine plus cytosine in the deoxyribonucleic acid (DNA), etc., are similar to those of most bifidobacteria. However, DNA-DNA hybridization studies revealed little or n o polynucleotide sequence similarity to any other members of the genus Bifidobacterium. We therefore regard these 26 strains as constituting a new species, for which we propose the name Bifidobacterium magnum. The type strain of this new species is RA3 (= ATCC 27 5 40).
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