Bifidobacterium is a genus of gram-positive, non-motile, often branched anaerobic bacteria. They are ubiquitous, endosymbiotic inhabitants of the gastrointestinal tract, vagina and mouth (B. dentium) of mammals, including humans. Bifidobacteria are one of the major genera of bacteria that make up the colon flora in mammals. Some bifidobacteria are used as probiotics.
Before the 1960s, Bifidobacterium species were collectively referred to as "Lactobacillus bifidus".
In 1899, Henry Tissier, a French pediatrician at the Pasteur Institute in Paris, isolated a bacterium characterised by a Y-shaped morphology ("bifid") in the intestinal flora of breast-fed infants and named it "bifidus". The scientist observed that these bifidobacteria were dominant in the gut flora of healthy babies. He thus noticed that when the bacteria were present in an infant's intestinal flora, the baby suffered less from gastrointestinal disorders. He therefore recommended treating infants suffering from diarrhea with the bacteria.
In 1907, Elie Metchnikoff, deputy director at the Pasteur Institute, propounded the theory that lactic acid bacteria are beneficial to human health. He observed that the longevity of Bulgarian peasants was the result of their consumption of fermented milk products. Elie Metchnikoff also suggested that “oral administration of cultures of fermentative bacteria would implant the beneficial bacteria in the intestinal tract”.
Some Bifidobacterium strains are considered as important probiotics and used in the food industry. Different species and/or strains of bifidobacteria may exert a range of beneficial health effects, including the regulation of intestinal microbial homeostasis, the inhibition of pathogens and harmful bacteria that colonize and/or infect the gut mucosa, the modulation of local and systemic immune responses, the repression of procarcinogenic enzymatic activities within the microbiota, the production of vitamins, and the bioconversion of a number of dietary compounds into bioactive molecules. Bifidobacterium improve the gut mucosal barrier and lowers levels of lipopolysaccharide in the intestine.
Mother's milk contains high concentrations of lactose and lower quantities of phosphate (pH buffer). Therefore, when mother's milk is fermented by lactic acid bacteria (incl. bifidobacteria) in the infant's gastrointestinal tract, the pH may be reduced, making it more difficult for gram-negative bacteria to grow.
The genus Bifidobacterium possesses a unique fructose-6-phosphate phosphoketolase pathway employed to ferment carbohydrates.
Much metabolic research on bifidobacteria has focused on oligosaccharide metabolism as these carbohydrates are available in their otherwise nutrient-limited habitats. Interestingly, infant-associated bifidobacterial phylotypes appear to have evolved the ability to ferment milk oligosaccharides, whereas adult-associated species utilize plant oligosaccharides, consistent with what they encounter in their respective environments. As breast-fed infants often harbor bifidobacteria dominated gut consortia, there have been numerous applications to mimic the bifidogenic properties of milk oligosaccharides. These are broadly classified as plant-derived fructo-oligosaccharides or dairy-derived galacto-oligosaccharides, which are differentially metabolized and distinct from milk oligosaccharide catabolism.
Response to oxygen
The sensitivity of members of the genus Bifidobacterium to O2 generally limits probiotic activity to anaerobic habitats. Recent research has reported that some Bifidobacterium strains exhibit various types of oxic growth. Low concentrations of O2 and CO2 can have a stimulatory effect on the growth of these Bifidobacterium strains. Based on the growth profiles under different O2 concentrations, the Bifidobacterium species were classified into four classes: O2-hypersensitive, O2-sensitive, O2-tolerant, and microaerophilic. The primary factor responsible for aerobic growth inhibition is proposed to be the production of hydrogen peroxide (H2O2) in the growth medium. A H2O2-forming NADH oxidase was purified from O2-sensitive Bifidobacterium bifidum and was identified as a b-type dihydroorotate dehydrogenase. The kinetic parameters suggested that the enzyme could be involved in H2O2 production in highly aerated environments.
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- Bifidobacterium at Microbe Wiki
- Genomes Online Database contains many Bifidobacterium genome projects
- Comparative Analysis of Bifidobacterium Genomes (at DOE's IMG system)
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