''Bifidobacterium'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

gram-positive In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. The Gram stain is ...

, nonmotile, often branched anaerobic

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

. They are ubiquitous inhabitants of the

gastrointestinal tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the Digestion, digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascula ...

though strains have been isolated from the

vagina In mammals and other animals, the vagina (: vaginas or vaginae) is the elastic, muscular sex organ, reproductive organ of the female genital tract. In humans, it extends from the vulval vestibule to the cervix (neck of the uterus). The #Vag ...

and mouth ('' B. dentium'') of mammals, including humans. Bifidobacteria are one of the major genera of bacteria that make up the gastrointestinal tract microbiota in mammals. Some bifidobacteria are used as probiotics. Before the 1960s, ''Bifidobacterium'' species were collectively referred to as ''Lactobacillus bifidus''.

History

In 1899, Henri Tissier, a French pediatrician at the Pasteur Institute in Paris, isolated a bacterium characterised by a Y-shaped morphology ("bifid") in the intestinal microbiota of breast-fed infants and named it "bifidus". In 1907, Élie Metchnikoff, deputy director at the Pasteur Institute, propounded the theory that lactic acid bacteria are beneficial to human health. Metchnikoff observed that the

longevity Longevity may refer to especially long-lived members of a population, whereas ''life expectancy'' is defined Statistics, statistically as the average number of years remaining at a given age. For example, a population's life expectancy at birth ...

of Bulgarians was the result of their consumption of fermented milk products. Metchnikoff also suggested that "oral administration of cultures of fermentative bacteria would implant the beneficial bacteria in the intestinal tract".

Metabolism

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. Infant-associated bifidobacterial phylotypes appear to have evolved the ability to ferment milk oligosaccharides, whereas adult-associated species use plant oligosaccharides, consistent with what they encounter in their respective environments. As breast-fed infants often harbor bifidobacteria-dominated gut consortia, numerous applications attempt to mimic the bifidogenic properties of milk oligosaccharides. These are broadly classified as plant-derived

fructooligosaccharide Fructooligosaccharides (FOS) also sometimes called oligofructose or oligofructan, are oligosaccharide fructans, used as an alternative sweetener. FOS exhibits sweetness levels between 30 and 50 percent of sugar in commercially prepared syrups. ...

s or dairy-derived galactooligosaccharides, 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.

Genomes

Members of the genus ''Bifidobacterium'' have genome sizes ranging from 1.73 (''Bifidobacterium indicum'') to 3.25 Mb (''Bifidobacterium biavatii''), corresponding to 1,352 and 2,557 predicted protein-encoding open reading frames, respectively. Functional classification of ''Bifidobacterium'' genes, including the pan-genome of this genus, revealed that 13.7% of the identified bifidobacterial genes encode enzymes involved in carbohydrate metabolism.

Clinical uses

Adding ''Bifidobacterium'' as a probiotic to conventional treatment of ulcerative colitis has been shown to be associated with improved rates of remission and improved maintenance of remission. 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 In biology, homeostasis (British English, British also homoeostasis; ) is the state of steady internal physics, physical and chemistry, chemical conditions maintained by organism, living systems. This is the condition of optimal functioning fo ...

, 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. Bifidobacteria improve the gut mucosal barrier and lower levels of lipopolysaccharide in the intestine. Bifidobacteria may also improve abdominal pain in patients with irritable bowel syndrome (IBS) though studies to date have been inconclusive. Naturally occurring ''Bifidobacterium'' spp. may discourage the growth of

Gram-negative Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is that their cell envelope consists ...

pathogens in infants. A 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 (including bifidobacteria) in the infant's gastrointestinal tract, the pH may be reduced, making it more difficult for Gram-negative bacteria to grow.

Bifidobacteria and the infant gut

The human infant gut is relatively sterile up until birth, where it takes up bacteria from its surrounding environment and its mother. The microbiota that makes up the infant gut differs from the adult gut. An infant reaches the adult stage of their microbiome at around three years of age, when their microbiome diversity increases, stabilizes, and the infant switches over to solid foods. Breast-fed infants are colonized earlier by ''Bifidobacterium'' when compared to babies that are primarily formula-fed. ''Bifidobacterium'' is the most common bacteria in the infant gut microbiome. There is more variability in genotypes over time in infants, making them less stable compared to the adult ''Bifidobacterium''. Infants and children under three years old show low diversity in microbiome bacteria, but more diversity between individuals when compared to adults. Reduction of ''Bifidobacterium'' and increase in diversity of the infant gut microbiome occurs with less breast-milk intake and increase of solid food intake. Mammalian milk all contain oligosaccharides showing natural selection . Human milk oligosaccharides are not digested by enzymes and remain whole through the digestive tract before being broken down in the colon by microbiota. ''Bifidobacterium'' species genomes of '' B. longum, B. bifidum, B. breve'' contain genes that can hydrolyze some of the human milk oligosaccharides and these are found in higher numbers in infants that are breast-fed. Glycans that are produced by the humans are converted into food and energy for the ''B. bifidum.'' showing an example of coevolution.

Species

The genus ''Bifidobacterium'' comprises the following species: * '' B. actinocoloniiforme'' Killer et al. 2011 * '' B. adolescentis'' Reuter 1963 (Approved Lists 1980) * '' B. aemilianum'' Alberoni et al. 2019 * '' B. aerophilum'' Michelini et al. 2017 * '' B. aesculapii'' Modesto et al. 2014 * '' B. amazonense'' Lugli et al. 2021 * '' B. angulatum'' Scardovi and Crociani 1974 (Approved Lists 1980) * '' B. animalis'' (Mitsuoka 1969) Scardovi and Trovatelli 1974 (Approved Lists 1980) * '' B. anseris'' Lugli et al. 2018 * '' B. apousia'' Chen et al. 2022 * '' B. apri'' Pechar et al. 2017 * '' B. aquikefiri'' Laureys et al. 2016 * '' B. asteroides'' Scardovi and Trovatelli 1969 (Approved Lists 1980) * '' B. avesanii'' Michelini et al. 2019 * '' B. biavatii'' Endo et al. 2012 * '' B. bifidum'' (Tissier 1900) Orla-Jensen 1924 (Approved Lists 1980) * '' B. bohemicum'' Killer et al. 2011 * '' B. bombi'' Killer et al. 2009 * '' B. boum'' Scardovi et al. 1979 (Approved Lists 1980) * '' B. breve'' Reuter 1963 (Approved Lists 1980) * '' B. callimiconis'' Duranti et al. 2019 * '' B. callitrichidarum'' Modesto et al. 2018 * '' B. callitrichos'' Endo et al. 2012 * '' B. canis'' Neuzil-Bunesova et al. 2020 * '' B. castoris'' Duranti et al. 2019 * '' B. catenulatum'' Scardovi and Crociani 1974 (Approved Lists 1980) * '' B. catulorum'' Modesto et al. 2018 * '' B. cebidarum'' Duranti et al. 2020 * '' B. choerinum'' Scardovi et al. 1979 (Approved Lists 1980) * '' B.choladohabitans '' Chen et al. 2022 * '' B. choloepi'' Modesto et al. 2020 * '' B. colobi'' Lugli et al. 2021 * '' B. commune'' Praet et al. 2015 * '' B. criceti'' Lugli et al. 2018 * "'' B. crudilactis''" Delcenserie et al. 2007 * '' B.cuniculi '' Scardovi et al. 1979 (Approved Lists 1980) * '' B. dentium'' Scardovi and Crociani 1974 (Approved Lists 1980) * '' B. dolichotidis'' Duranti et al. 2019 * "'' B. eriksonii''" Cato et al. 1970 * '' B. erythrocebi'' Neuzil-Bunesova et al. 2021 * '' B. eulemuris'' Michelini et al. 2016 * '' B. faecale'' Choi et al. 2014 * '' B. felsineum'' Modesto et al. 2020 * '' B. gallicum'' Lauer 1990 * '' B. gallinarum'' Watabe et al. 1983 * '' B. globosum'' (ex Scardovi et al. 1969) Biavati et al. 1982 * '' B. goeldii'' Duranti et al. 2019 * '' B. hapali'' Michelini et al. 2016 * '' B. '' Lugli et al. 2018 * '' B. indicum'' Scardovi and Trovatelli 1969 (Approved Lists 1980) * '' B. italicum'' Lugli et al. 2018 * '' B. jacchi'' Modesto et al. 2019 * '' B. lemurum'' Modesto et al. 2015 * '' B. leontopitheci'' Duranti et al. 2020 * '' B. longum'' Reuter 1963 (Approved Lists 1980) * '' B. magnum'' Scardovi and Zani 1974 (Approved Lists 1980) * '' B.margollesii '' Lugli et al. 2018 * '' B. merycicum'' Biavati and Mattarelli 1991 * '' B. miconis'' Lugli et al. 2021 * '' B. miconisargentati'' Lugli et al. 2021 * '' B. minimum'' Biavati et al. 1982 * '' B. mongoliense'' Watanabe et al. 2009 * '' B. moraviense'' Neuzil-Bunesova et al. 2021 * '' B. moukalabense'' Tsuchida et al. 2014 * '' B. myosotis'' Michelini et al. 2016 * '' B. oedipodis'' Neuzil-Bunesova et al. 2021 * '' B. olomucense'' Neuzil-Bunesova et al. 2021 * '' B. panos'' Neuzil-Bunesova et al. 2021 * '' B. parmae'' Lugli et al. 2018 * "'' B. platyrrhinorum''" Modesto et al. 2020 * '' B. pluvialisilvae'' Lugli et al. 2021 * '' B. polysaccharolyticum'' Chen et al. 2022 * '' B. pongonis'' Lugli et al. 2021 * '' B. porcinum'' (Zhu et al. 2003) Nouioui et al. 2018 * '' B. primatium'' Modesto et al. 2020 * '' B. pseudocatenulatum'' Scardovi et al. 1979 (Approved Lists 1980) * '' B. pseudolongum'' Mitsuoka 1969 (Approved Lists 1980) * '' B. psychraerophilum'' Simpson et al. 2004 * '' B. pullorum'' Trovatelli et al. 1974 (Approved Lists 1980) * '' B. ramosum'' Michelini et al. 2017 * '' B. reuteri'' Endo et al. 2012 * '' B. rousetti'' Modesto et al. 2021 * "'' B. ruminale''" Scardovi et al. 1969 * '' B. ruminantium'' Biavati and Mattarelli 1991 * '' B. saguini'' Endo et al. 2012 * '' B. saguinibicoloris'' Lugli et al. 2021 * "'' B. saimiriisciurei''" Modesto et al. 2020 * '' B. samirii'' Duranti et al. 2019 * '' B. santillanense'' Lugli et al. 2021 * '' B. scaligerum'' Modesto et al. 2020 * '' B. scardovii'' Hoyles et al. 2002 * '' B. simiarum'' Modesto et al. 2020 * '' B. simiiventris'' Lugli et al. 2021 * '' B. stellenboschense'' Endo et al. 2012 * '' B. subtile'' Biavati et al. 1982 * '' B. thermacidophilum'' Dong et al. 2000 * '' B. thermophilum'' corrig. Mitsuoka 1969 (Approved Lists 1980) * '' B. tibiigranuli'' Eckel et al. 2020 * '' B. tissieri'' corrig. Michelini et al. 2016 * '' B. tsurumiense'' Okamoto et al. 2008 * "'' B. urinalis''" Hojo et al. 2007 * '' B. vansinderenii'' Duranti et al. 2017 * '' B. vespertilionis'' Modesto et al. 2021 * '' B. xylocopae'' Alberoni et al. 2019

References

External links

Bifidobacterium
a
Microbe Wiki

Genomes Online Database
contains many Bifidobacterium genome projects
Comparative Analysis of Bifidobacterium Genomes
(at DOE's IMG system)
''Bifidobacterium'' at Bac''Dive'' - the Bacterial Diversity MetadatabaseSpotlight on BifidobacteriaRadiolab podcast
Bifidobacterium Infantis in particular {{Authority control Bifidobacteriales Gut flora bacteria Bacterial vaginosis Bacteria genera