Summerbell Richard C, Moore Mary K, Starink-Willemse Mieke, Van Iperen Arien
CBS Fungal Biodiversity Centre, Utrecht, the Netherlands.
Med Mycol. 2007 May;45(3):193-200. doi: 10.1080/13693780601087614.
Early molecular biosystematic studies of dermatophytes created considerable confusion about the taxonomic status of the horse-associated Trichophyton equinum vis-à-vis the anthropophilic T. tonsurans. Though this matter has recently been clarified, routine identification of these species based on the commonly used ribosomal internal transcribed spacer (ITS) sequence has been impractical. This is because, in the available sequences attributed to the species in GenBank, a clear species-level distinction does not appear to exist. In the present study, resequencing the ITS regions of several anomalous isolates is shown to eliminate this problem, which was mainly based on read errors in older sequences. Newly generated sequences and recent GenBank additions are analysed to show that T. equinum appears to be uniform in ITS sequence worldwide, while T. tonsurans is also uniform, excepting a single-base change found in one otherwise typical strain. Analysis also reveals a distinct, as yet incompletely classified Asian genotype that may belong to one or the other of these species. Standard ITS 'barcode sequences' are proposed for T. tonsurans and T. equinum, and a taxonomic neotype is designated to anchor the latter species. T. equinum var. autotrophicum is further evidenced as very closely related to T. equinum var. equinum, and the anomaly of its plesiomorphous phenotype is discussed in a population genetics context.
早期对皮肤癣菌的分子生物系统学研究，使与马相关的马毛癣菌相对于亲人性的断发毛癣菌的分类地位产生了相当大的混乱。尽管此事最近已得到澄清，但基于常用的核糖体内部转录间隔区（ITS）序列对这些菌种进行常规鉴定一直不切实际。这是因为，在GenBank中归因于这些菌种的现有序列中，似乎不存在明确的种级区分。在本研究中，对几个异常分离株的ITS区域进行重新测序表明可消除这一问题，该问题主要基于旧序列中的读取错误。对新生成的序列和GenBank最近新增的序列进行分析表明，马毛癣菌在全球范围内的ITS序列似乎是一致的，而断发毛癣菌也是一致的，只是在一个其他方面典型的菌株中发现了一个单碱基变化。分析还揭示了一种独特的、尚未完全分类的亚洲基因型，它可能属于这两个菌种中的一个。提出了断发毛癣菌和马毛癣菌的标准ITS“条形码序列”，并指定了一个分类新模式来确定后一个菌种。马毛癣菌嗜养变种被进一步证明与马毛癣菌马变种密切相关，并在群体遗传学背景下讨论了其近祖表型的异常情况。
