Abstract
Although the genus Bifidobacterium was originally named for its bifid morphology, not all bifidobacterial species have a similar structure, and very few of them adopt a bifid shape under stress conditions. The exposure of respective bifidobacterial species to various conditions, such as different pH, temperatures, medium components, in vivo growth in Caenorhabditis elegans, and subculture, did not affect their diverse morphologies. Extensive scanning electron microscopy studies suggested that the bifid shape of B. adolescentis are maintained irrespective of the conditions. Hence, we conclude that the bifid morphology is intrinsic to B. adolescentis. Most bifidobacterial species are anaerobic and rod-shaped, whereas, after the first generation, they become microaerophilic or aerophilic. CaCl2 (treatment of B. animalis) signaling triggered a change from the rod shape to the bifid shape and vice versa in B. adolescentis.
Highlights
The genus Bifidobacterium is so designated because in the reference species, one end was a rocketshaped and the other, longitudinally split (Tissier, 1900)
We examine the polymorphic morphologies of the Bifidobacterium, and conclude that the bifid morphology is an intrinsic characteristic of B. adolescentis, whereas other species, including B. animalis, display polymorphic behavior only under stress conditions
We conclude that the Bifidobacterium species are microaerophilic because they can grow in the presence of a certain level of oxygen after the first generation
Summary
The genus Bifidobacterium is so designated because in the reference species, one end was a rocketshaped and the other, longitudinally split (Tissier, 1900). The lack of cutting-edge research into the taxonomy of the genus Bifidobacterium has meant that these species have been retained in Bifidobacterium, regardless of morphological differences. Because very few bifidobacterial strains have a bifid shape, even though some are polymorphic both rod-shaped and bifid-shaped species are retained in the single genus Bifidobacterium. Exposure to stress conditions causes the latter to adopt pleomorphic forms, including the bifid form. These observations were confirmed by Rodella (1908), Cruickshank (1925), Roos (1927), and Synder et al (1967) who reported that the alternative forms are uncommon and give an illusion of branching.
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