Oral Biosciences, Faculty of Dentistry, The University of Hong Kong, Prince Philip Dental Hospital, 34 Hospital Road, Sai Ying Pun, Hong Kong.
BMC Microbiol. 2013 Feb 4;13:24. doi: 10.1186/1471-2180-13-24.
The oral spirochete bacterium Treponema denticola is associated with both the incidence and severity of periodontal disease. Although the biological or phenotypic properties of a significant number of T. denticola isolates have been reported in the literature, their genetic diversity or phylogeny has never been systematically investigated. Here, we describe a multilocus sequence analysis (MLSA) of 20 of the most highly studied reference strains and clinical isolates of T. denticola; which were originally isolated from subgingival plaque samples taken from subjects from China, Japan, the Netherlands, Canada and the USA.
The sequences of the 16S ribosomal RNA gene, and 7 conserved protein-encoding genes (flaA, recA, pyrH, ppnK, dnaN, era and radC) were successfully determined for each strain. Sequence data was analyzed using a variety of bioinformatic and phylogenetic software tools. We found no evidence of positive selection or DNA recombination within the protein-encoding genes, where levels of intraspecific sequence polymorphism varied from 18.8% (flaA) to 8.9% (dnaN). Phylogenetic analysis of the concatenated protein-encoding gene sequence data (ca. 6,513 nucleotides for each strain) using Bayesian and maximum likelihood approaches indicated that the T. denticola strains were monophyletic, and formed 6 well-defined clades. All analyzed T. denticola strains appeared to have a genetic origin distinct from that of 'Treponema vincentii' or Treponema pallidum. No specific geographical relationships could be established; but several strains isolated from different continents appear to be closely related at the genetic level.
Our analyses indicate that previous biological and biophysical investigations have predominantly focused on a subset of T. denticola strains with a relatively narrow range of genetic diversity. Our methodology and results establish a genetic framework for the discrimination and phylogenetic analysis of T. denticola isolates, which will greatly assist future biological and epidemiological investigations involving this putative 'periodontopathogen'.
口腔螺旋体细菌 Treponema denticola 与牙周病的发生和严重程度都有关。尽管文献中已经报道了相当数量的 T. denticola 分离株的生物学或表型特性，但它们的遗传多样性或系统发育从未得到系统研究。在这里，我们描述了对 20 株最受研究的参考株和临床分离株的多基因序列分析（MLSA）；这些分离株最初是从来自中国、日本、荷兰、加拿大和美国的受试者的龈下菌斑样本中分离出来的。
成功地为每个菌株确定了 16S 核糖体 RNA 基因和 7 个保守的蛋白质编码基因（flaA、recA、pyrH、ppnK、dnaN、era 和 radC）的序列。使用各种生物信息学和系统发育软件工具对序列数据进行了分析。我们没有发现蛋白质编码基因内存在正选择或 DNA 重组的证据，种内序列多态性水平从 18.8%（flaA）到 8.9%（dnaN）不等。使用贝叶斯和最大似然方法对串联蛋白质编码基因序列数据（每个菌株约 6513 个核苷酸）进行的系统发育分析表明，T. denticola 菌株是单系的，形成了 6 个明确的分支。所有分析的 T. denticola 菌株似乎都具有与“Treponema vincentii”或苍白密螺旋体不同的遗传起源。没有建立特定的地理关系；但是，一些来自不同大陆的分离株在遗传水平上似乎密切相关。
我们的分析表明，以前的生物学和生物物理研究主要集中在遗传多样性相对狭窄的 T. denticola 菌株子集上。我们的方法和结果为 T. denticola 分离株的鉴别和系统发育分析建立了遗传框架，这将极大地帮助未来涉及这种假定的“牙周病原体”的生物学和流行病学研究。
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