Bifidobacterium animalis

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File:Http://microbewiki.kenyon.edu/index.php/Bifidobacterium
Scientific classification
Kingdom: Bacteria Phylum: Firmicutes Class: Actinobacteria Order: Bifidobacteriales Family: Bifidobacteriaceae Genus: Bifidobacterium Species: B. animalis
Binomial name
Bifidobacterium animalis

Description and significance

Gram positive (staining purple), Basillus (rod-shaped), anaerobic (no oxygen necessary for growth), non-spore forming and non-motile bacteria. This bacteria is occasionally found in a large intestine of most mammals including humans. These bacteria are recognized as the ones that play a crucial role in keeping the microbial balance of a healthy intestinal tract. These bacteria are commonly used as probiotics(dietary supplements of live bacteria that are beneficial for the host's health). Bifidobacteria help digest food, they are also associated with the decreased occurrence of allergies. Moreover, this bacteria are considered to prevent several forms of tumor growth. The probiotics are usually obtained through dairy products and dried food supplements. These bacteria posses a heterofermentative ability, hence they can make lactic acid and ethanol along with several short-chain fatty acids-this includes acidic acid and formic acid. It has also been suggested by a various investigators that the production of small amounts of succinic acid as well as carbon dioxide is also possible by Bifidobacterium strains. The change of intestinal ph happening during carbohydrate fermentation which is created by acidic metabolites has the ability to inhibit the growth of not-desirable, potentially harmful (pathogenic) bacteria. Bifidobacteria yet induces various other significant benefits to their host (symbiotic relationship), those benefits include: production of vitamins, immunostimulating effects(yielding a protection against infections), the lowering of a cholesterol.

Genome structure

The main biological functions are coded by a single circular chromosome which is approximately 1,933,965 bp.There are no plasmids present. The genome codes for 1,528 coding sequences, two rRNA operons, and 52 tRNA genes. There are no functional prophages that were identified so far from this particular genome sequence, though a few phage-related genes including integrases were discovered. There is a fos gene cluster that has been identified through the genome analysis, this cluster is directly involved in the processing of the health promoting fructooligosachirides - also known as the bifidogenic factors. A substantial portion of the genome approximately 787 kb is suggested to be devoted to the polysaccharide synthesis. Polysaccharides that are synthesized in the gut microorganisms are considered as candidates for probiotic factors. There is a gene (bla_1379) that encodes the bile salt hydrolase. The genome sequencing suggests that this may be a factor responsible for the bacterium's successive tolerance to bile acids. Even though there was a substantial amount of research done so far, the entire genome structure of Bifidobacterium still appears to be meager.

Cell structure and metabolism

The temperature in a range 37-41 C appears to be the most optimal for the growth. Moreover, no growth appears at the temperature below 20 C, and above 46 C. Bifidobacterium are considered acid-tolerant species. The ph around 6.5-7 is considered to be optimal. No growth occurs at ph lower than 4.5, and above 8.5. Bifidobacterium are defined as anaerobic, nonetheless the oxygen sensitivity varies within the species, and between the strains of each species respectively. The fructose-6-phosphate phosphoketolase is believed to be the key enzyme of the hexose catabolism in Bifidobacteria. The enzyme splits the hexose phosphate into erythrose-4-phosphate and acetyl phosphate. Furthermore, from hexose phosphates and tetrose, via the subsequent action of transaldolase and transketolase, pentose phosphates are made, which then, undergo the 2,3 cleavage yield the lactic acid and the extra amounts of the acetic acid. The synthesis of the formic acid and ethanol can effect the fermentation equilibrium. Hence, various organisms make different amounts of acetate, lactate ethanol and formate under the relative equal conditions. Bifidobacterium requires substances such as N-acetylglucosamine, B-substitute disacchride, N-acetyllactosamine which are components that are found in milk, those components promote bacterial growth.

The Bifidubacterium has a cell wall structure that is typical representative of the Gram positive bacteria structure. It consists of a thick peptydoglican envelope with polysaccharides, proteins and teichoic acids embedded in it. The composition of amino acids varies among species, this permits the actual differentiation between them. The polymers to be excreted may have the structure that results from repeated subunits of glucose, galactose, and small amounts of uronic acids and hexoamines. The links that are formed by the union of lipoteichoic acids with the polysaccharide chains are believed to be crucial factors of cell adhesion to the wall of intestine. Some members of the Bifidebacteria possess the lipoglycans of different structure, in this case the amino acid L-alanine is substituted by its D-isomer. The further immunochemical studies demonstrate that the lipoteichoic acids are also a common antigens within the entire genus of Bifidobacterium. Therefore, proteins and lipoteichoic acids determine the hydrophobicity of the surface of this bacteria. Moreover, the research upon the nature of the hydrolyzing enzymes of the cell wall of Bifidobacterium illustrated several kinds of such enzymes that vary in molecular weight based on a strain.

References

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