ビフィズス菌

Bifidobacterium/ja
	ビフィドバクテリウム・アドレッセンティス
Scientific classification
Domain:	Bacteria
Phylum:	Actinomycetota
Class:	Actinomycetia
Order:	Bifidobacteriales
Family:	Bifidobacteriaceae
Genus:	Bifidobacterium; Orla-Jensen 1924 (Approved Lists 1980)
Type species
	Bifidobacterium bifidum/ja; (Tissier 1900) Orla-Jensen 1924 (Approved Lists 1980)
Species
	See text.

乳酸菌(Bifidobacterium)は、グラム陽性で非運動性、しばしば分岐した嫌気性細菌の属である。ビフィズス菌は消化管に偏在しているが、ヒトを含む哺乳類の膣や口腔（B. dentium）からも分離されている。ビフィズス菌は、哺乳類の消化管微生物叢を構成する主要な細菌属のひとつである。一部のビフィズス菌はプロバイオティクスとして使用されている。

1960年代以前は、ビフィドバクテリウム種はラクトバチルス・ビフィズスと総称されていた。

歴史

アクティヴィアヨーグルトのサンプルから見つかったビフィドバクテリウム・アニマリス菌の一部: 目盛りの数字の目盛りは10マイクロメートル離れている。

1899年、パリのパスツール研究所のフランス人小児科医であったアンリ・ティシエは、母乳で育てられた乳児の腸内細菌叢からY字型の形態（「ビフィズス」）を特徴とする細菌を分離し、「ビフィズス菌」と命名した。1907年、パスツール研究所の副所長であったエリー・メチニコフは、乳酸菌が人間の健康に有益であるという理論を提唱した。メチニコフはブルガリア人の長寿は発酵乳製品の摂取の結果であると観察した。メチニコフはまた、「発酵菌の培養物を経口投与することで、腸管内に有益な細菌が着床する」とも示唆した。

代謝

ビフィズス菌属は、炭水化物を発酵させるために使用されるユニークなフルクトース-6-リン酸ホスホケトラーゼ経路を持っている。

ビフィズス菌の代謝研究の多くはオリゴ糖代謝に焦点を当てている。乳児に関連するビフィズス菌の系統型はミルクオリゴ糖を発酵する能力を進化させたようであるが、成人に関連する種は植物オリゴ糖を使用し、それぞれの環境で遭遇するものと一致している。母乳栄養の乳児はビフィズス菌が優勢な腸内コンソシアを持つことが多いため、ミルクオリゴ糖のビフィズス形成特性を模倣しようとする応用が数多く試みられている。これらは植物由来のフラクトオリゴ糖または乳製品由来のガラクトオリゴ糖に大別され、ミルクオリゴ糖異化とは異なる代謝を受ける。

酸素への反応

ビフィズス菌属のメンバーは酸素₂に敏感であるため、一般的にプロバイオティクスの活性は嫌気性の生息環境に限定される。最近の研究では、いくつかのビフィドバクテリウム株が様々なタイプのoxic増殖を示すことが報告されている。低濃度のO₂やCO₂は、これらのビフィズス菌株の増殖に刺激的な効果をもたらす。異なるO₂濃度下での増殖プロファイルに基づき、Bifidobacterium種は4つのクラスに分類された： O₂-過敏性、O₂-感受性、O₂-耐性、そして微好気性である。好気性増殖阻害の主な要因は、増殖培地中の過酸化水素（H₂O₂）の生成であると提唱されている。O₂感受性のBifidobacterium bifidumを精製し、H₂O₂を形成するNADH オキシダーゼが発見された。b型ジヒドロオロテートデヒドロゲナーゼと同定した。この酵素は、高好気性環境におけるH₂O₂産生に関与している可能性が示唆された。

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, 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 pathogens in infants.

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

外部リンク

Bifidobacterium at Microbe Wiki
Genomes Online Database contains many Bifidobacterium genome projects
Comparative Analysis of Bifidobacterium Genomes (at DOE's IMG system)
Bifidobacterium at BacDive - the Bacterial Diversity Metadatabase
Spotlight on Bifidobacteria