High frequency intragenomic heterogeneity of the ribosomal DNA intergenic spacer region in Trichophyton violaceum

Department of Medical Laboratory Science and Biotechnology; and Department of Dermatology, College of Medicine, National Cheng Kung University, 1 University Road, Tainan, 701, Taiwan; Mycology Reference Centre, The General Infirmary at Leeds, Leeds LS1 3EX, UK; School of Medicine, Swansea University, Singleton Park, Swansea SA2 8PP, UK

^* To whom correspondence should be addressed. Email: jcjc{at}mail.ncku.edu.tw.

	Abstract

The intergenic spacer (IGS) of the ribosomal RNA genes was analyzed from the dermatophyte Trichophyton violaceum isolated from cases of tinea capitis in Taiwan and Iran. T. violaceum strains were cultured from different colonies, from single conidial colonies derived by dilution plating and from micromanipulation of single conidium from clinical samples. A ribosomal DNA probe hybridizing to multiple EcoRI fragments was used to compare restriction fragment length polymorphisms (RFLP) in different T. violaceum isolates. The arthroconidia of T. violaceum that form in vivo during infection were shown to contain a single nucleus by transmission electron microscopy. IGS regions from an isolate cultured from a single conidium were amplified, cloned and sequenced. The results identified that heterogeneity exists between IGS regions within a single T. violaceum genome due to different copy numbers of a 171 bp tandem repeat. This suggests that the IGS of T. violaceum is partially excluded from the concerted evolution of the rRNA gene locus. The heterogeneous character of the IGS regions in T. violaceum contrasts with the closely related dermatophyte, Trichophyton rubrum posing further questions on the phylogeny and the evolution of dermatophyte fungi.