Higher Order Classification
Description and Significance
Bifidobacterium animalis is a branched, rod-shaped (diplobicillus) gram-positive bacteria. This bacteria is generally found in the large intestines of mammals such as: cats, cows, and humans. Discovered by Henry Tissier in 1900 Bifidobacterium animalis was isolated from a breast-fed infant.
Although it was discovered in 1900, research on this bacterium did not ensue until the interest in probiotics in 1950. Probiotics are microorganisms that are ingested either in combination or as a single organism in an effort to normalize intestinal microbiota and potentially improve intestinal barrier function. It has long been speculation that probiotics are useful in alleviating or curing the symptoms associated with irritable bowel syndrome, ulcerative collitis, diarrhea, and atopic dermatitis.
Bifidobacterium animalis contains one circular chromosome consisting of 1, 943, 990 base pairs with a G-C content of 60.5% which is similar to all members of Bifidobacterium. The bacterium carries 1,560 open reading frames (OFRs), 52 tRNA operons, 4 rRNA operons, and a 36 base pair cluster of regularly interspersed short palindromic repeat (CRISPR).
Cell Structure, Metabolism and Life Cycle
Bifidobacterium animalis contains all of the traditional elements of rod-shaped bacteria including organelles, a plasmid, a cell membrane, and cell wall but not a flagella. Recent studies of the extracellular polysaccharides of the cell envelope have found high RHa residue and terminal Gal furanoside, which has been postulated to interact with the mucous community of the intestines.
Bifidobacterium animalis is an anaerobic chemoorganotroph that undergoes lactic acid fermentation. Lactic acid fermentation is the process by which six-carbon sugars like glucose are converted into cellular energy and lactate in the absence of oxygen. Lactic acid in the intestines is hypothesized to aid in the hydrolysis of lactose which is not easily broken down. "Bifidobacteria can utilize a diverse range of dietary carbohydrates that escape degradation in the upper parts of the intestine, many of which are plant-derived oligo- and polysaccharides" .
Like most prokaryotic bacteria, Bifidobacterium animalis reproduces and continues it's life cycle through binary fission which is a form of asexual reproduction that involves replicating the cell's genetic material followed by the parent cell dividing into two equal sized daughter cells that are clones. 
Bifidobacterium animalis has an ecological habitat that helps make up the colon flora of most mammals. It resides mainly in the large intestine in a pH from 5.5-7. This bacterium is commonly cultured in a MRS broth at 37 degrees Celsius.
Much research has gone into deciphering what element plays into the symbiotic relationship that probiotics like Bifidobacterium animalis form with the gastrointestinal tract of most mammals. The formation of lactic acid allows for the hydrolysis of lactose and other complex sugars, and it is believed that sugars present on the membrane of the bacterium are capable of interacting with the mucous lining of the large intestines. This structure of sugars along the membrane are believed to contribute to the bacteria's ability to regulate biological and physiological functionalities in the host gastrointestinal tract.
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Page authored by Paul Proctor & Benjamin McKinnon-Duggins, student of Prof. Jay Lennon at IndianaUniversity.