意大利帕爾馬大學(xué)的微生物學(xué)家對(duì)齒雙歧桿菌(Bifidobacterium dentium)基因組測(cè)序發(fā)現(xiàn)，齒雙歧桿菌能使大量的糖產(chǎn)生代謝變化,，并在酸性環(huán)境中存活,，可抵抗漱口水的沖洗,。
Marco Ventura最初開始對(duì)齒雙歧桿菌進(jìn)行研究時(shí)，他并未想過它們與蛀牙有關(guān),。事實(shí)上,，他只是對(duì)整個(gè)雙歧桿菌屬感興趣——它們構(gòu)成了消化道中的大部分細(xì)菌，并且被認(rèn)為對(duì)健康有益,。然而齒雙歧桿菌可能并不會(huì)促進(jìn)健康,。這種細(xì)菌被發(fā)現(xiàn)于牙齒的空洞中，并被認(rèn)為是造成蛀牙的罪魁禍?zhǔn)?。為了搞清是什么讓齒雙歧桿菌與它的親戚有如此大的差別，Ventura和同事對(duì)這種細(xì)菌的基因組進(jìn)行了測(cè)序,。
齒雙歧桿菌的基因組揭示了一些為在口腔中生存而作出的一流改變,。研究小組在12月24日的《科學(xué)公共圖書館—遺傳學(xué)》雜志網(wǎng)絡(luò)版上報(bào)告了這一研究成果。與其他位于消化道中的雙歧桿菌相比,，齒雙歧桿菌擁有更多基因,，旨在合成用來分解糖的酶——與生活在消化道中的細(xì)菌能夠穩(wěn)定地得到來自胃部的碳水化合物不同，生活在口腔中的齒雙歧桿菌不得不學(xué)會(huì)在任何條件下抓住任何機(jī)會(huì)分解到手的糖分,。
對(duì)齒雙歧桿菌基因組的研究同時(shí)也揭示了它們?yōu)槭裁词侨绱穗y以被抑制,。它們通過大量基因增加了自己在酸性環(huán)境中的表達(dá)，這或許有助于它們?cè)谘狼恢械拇婊?mdash;—這里的酸性物質(zhì)破壞了牙齒的琺瑯質(zhì),。齒雙歧桿菌甚至已經(jīng)進(jìn)化出了一種使自己免遭口腔衛(wèi)生行為攻擊的方法——當(dāng)Ventura和同事在不同的漱口水和殺菌劑中培養(yǎng)齒雙歧桿菌后,，他們發(fā)現(xiàn)，這種細(xì)菌會(huì)調(diào)整幾種基因的活性,，后者能夠合成與有毒化合物捆綁在一起并可使它們無害的蛋白質(zhì),。
美國波士頓市Forsyth研究所的微生物學(xué)家Floyd Dewhirst表示，如今,，科學(xué)家已經(jīng)知道齒雙歧桿菌是怎樣運(yùn)作的,，或許他們很快就會(huì)研制出消滅這種細(xì)菌的方法。例如,，研究人員可以開發(fā)出一種藥物,，用來攻擊細(xì)菌控制其內(nèi)部pH值的酶。
然而Ventura強(qiáng)調(diào),，在口腔中還有其他許多能夠?qū)е轮赖募?xì)菌,，因此僅僅消滅一種細(xì)菌并不會(huì)讓牙科醫(yī)生下崗。英國布里斯托爾大學(xué)的口腔微生物學(xué)家Howard Jenkinson補(bǔ)充說,，在很多情況下,，我們已經(jīng)知道如何防止牙齒的腐蝕,。他表示：“防止蛀牙的最佳方式是通過氟化物，以及教育人們不要飲用含糖的飲料,。”（生物谷Bioon.com）
生物谷推薦原始出處：
PLoS Genet 5(12): e1000785. doi:10.1371/journal.pgen.1000785
The Bifidobacterium dentium Bd1 Genome Sequence Reflects Its Genetic Adaptation to the Human Oral Cavity
Marco Ventura1*, Francesca Turroni1, Aldert Zomer2, Elena Foroni1, Vanessa Giubellini1, Francesca Bottacini1, Carlos Canchaya1, Marcus J. Claesson2, Fei He3, Maria Mantzourani4, Laura Mulas5, Alberto Ferrarini6, Beile Gao7, Massimo Delledonne6, Bernard Henrissat8, Pedro Coutinho8, Marco Oggioni5, Radhey S. Gupta7, Ziding Zhang3, David Beighton4, Gerald F. Fitzgerald2, Paul W. O'Toole2, Douwe van Sinderen2*
1 Laboratory of Probiogenomics, Department of Genetics, Biology of Microorganisms, Anthropology, and Evolution, University of Parma, Parma, Italy, 2 Alimentary Pharmabiotic Centre and Department of Microbiology, Bioscience Institute, National University of Ireland, Cork, Ireland, 3 College of Biological Sciences, China Agricultural University, Beijing, China, 4 Department of Microbiology, The Henry Wellcome Laboratories for Microbiology and Salivary Research, Kings College London Dental Institute, London, United Kingdom, 5 Department of Molecular Biology, University of Siena, Siena, Italy, 6 Dipartimento Sientifico Tecnologico, Università degli Studi di Verona, Verona, Italy, 7 Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario, Canada, 8 Glycogenomics, Databases, and Bioinformatics, Architecture et Fonction des Macromolécules Biologiques, Universités Aix-Marseille, Marseille, France
Bifidobacteria, one of the relatively dominant components of the human intestinal microbiota, are considered one of the key groups of beneficial intestinal bacteria (probiotic bacteria). However, in addition to health-promoting taxa, the genus Bifidobacterium also includes Bifidobacterium dentium, an opportunistic cariogenic pathogen. The genetic basis for the ability of B. dentium to survive in the oral cavity and contribute to caries development is not understood. The genome of B. dentium Bd1, a strain isolated from dental caries, was sequenced to completion to uncover a single circular 2,636,368 base pair chromosome with 2,143 predicted open reading frames. Annotation of the genome sequence revealed multiple ways in which B. dentium has adapted to the oral environment through specialized nutrient acquisition, defences against antimicrobials, and gene products that increase fitness and competitiveness within the oral niche. B. dentium Bd1 was shown to metabolize a wide variety of carbohydrates, consistent with genome-based predictions, while colonization and persistence factors implicated in tissue adhesion, acid tolerance, and the metabolism of human saliva-derived compounds were also identified. Global transcriptome analysis demonstrated that many of the genes encoding these predicted traits are highly expressed under relevant physiological conditions. This is the first report to identify, through various genomic approaches, specific genetic adaptations of a Bifidobacterium taxon, Bifidobacterium dentium Bd1, to a lifestyle as a cariogenic microorganism in the oral cavity. In silico analysis and comparative genomic hybridization experiments clearly reveal a high level of genome conservation among various B. dentium strains. The data indicate that the genome of this opportunistic cariogen has evolved through a very limited number of horizontal gene acquisition events, highlighting the narrow boundaries that separate commensals from opportunistic pathogens.
