意大利帕尔马大学的微生物学家对齿双歧杆菌(Bifidobacterium dentium)基因组测序发现，齿双歧杆菌能使大量的糖产生代谢变化，并在酸性环境中存活，可抵抗漱口水的冲洗。
Marco Ventura最初开始对齿双歧杆菌进行研究时，他并未想过它们与蛀牙有关。事实上，他只是对整个双歧杆菌属感兴趣——它们构成了消化道中的大部分细菌，并且被认为对健康有益。然而齿双歧杆菌可能并不会促进健康。这种细菌被发现于牙齿的空洞中，并被认为是造成蛀牙的罪魁祸首。为了搞清是什么让齿双歧杆菌与它的亲戚有如此大的差别，Ventura和同事对这种细菌的基因组进行了测序。
齿双歧杆菌的基因组揭示了一些为在口腔中生存而作出的一流改变。研究小组在12月24日的《科学公共图书馆—遗传学》杂志网络版上报告了这一研究成果。与其他位于消化道中的双歧杆菌相比，齿双歧杆菌拥有更多基因，旨在合成用来分解糖的酶——与生活在消化道中的细菌能够稳定地得到来自胃部的碳水化合物不同，生活在口腔中的齿双歧杆菌不得不学会在任何条件下抓住任何机会分解到手的糖分。
对齿双歧杆菌基因组的研究同时也揭示了它们为什么是如此难以被抑制。它们通过大量基因增加了自己在酸性环境中的表达，这或许有助于它们在牙腔中的存活——这里的酸性物质破坏了牙齿的珐琅质。齿双歧杆菌甚至已经进化出了一种使自己免遭口腔卫生行为攻击的方法——当Ventura和同事在不同的漱口水和杀菌剂中培养齿双歧杆菌后，他们发现，这种细菌会调整几种基因的活性，后者能够合成与有毒化合物捆绑在一起并可使它们无害的蛋白质。
美国波士顿市Forsyth研究所的微生物学家Floyd Dewhirst表示，如今，科学家已经知道齿双歧杆菌是怎样运作的，或许他们很快就会研制出消灭这种细菌的方法。例如，研究人员可以开发出一种药物，用来攻击细菌控制其内部pH值的酶。
然而Ventura强调，在口腔中还有其他许多能够导致蛀牙的细菌，因此仅仅消灭一种细菌并不会让牙科医生下岗。英国布里斯托尔大学的口腔微生物学家Howard Jenkinson补充说，在很多情况下，我们已经知道如何防止牙齿的腐蚀。他表示：“防止蛀牙的最佳方式是通过氟化物，以及教育人们不要饮用含糖的饮料。”（生物谷Bioon.com）
生物谷推荐原始出处：
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.
