PHYLOGENY OF DERMATOPHYTES AND DIMORPHIC FUNGI BASED ON LARGE SUBUNITRIBOSOMAL-RNA SEQUENCE COMPARISONS

The phylogeny of dermatophytes and dimorphic fungi was considered usin g the large-subunit of ribosomal RNA (25S rRNA). Aligned sequences of 595 nucleotides covering the two most divergent domains D1 and D2, per mitted a comparison of phylogenetic relationships at different levels. The dimorphic species (Onygenaceae) were significantly separated from dermatophytes (Arthrodermataceae) and from a third group including ge ophilic or very weakly pathogenic species (Onygenaceae and Gymnoascace ae). On a species level, the varietal status of Histoplasma duboisii a nd Histoplasma farciminosum, as close relations of Histoplasma capsula tum, was confirmed. The dimorphic fungus Emmonsia parva, in spite of a completely different parasitic form (adiaspores instead of yeast-like cells), clustered with Blastomyces dermatitidis which has a perfect f orm resembling that of H. capsulatum. From our data, teleomorphs of E. parva Paracoccidioides brasiliensis and H. farciminosum, three dimorp hic fungi known only under their anamorphic states, should belong to t he family of Onygenaceae and the genus Ajellomyces. Among Arthrodermat aceae, and family containing the most keratinophilic species, it was n ot possible to establish a clear hierarchy of species. Only Ctenomyces serratus, the species adapted to degrade keratin of feathers, Trichop hyton ajelloi and Trichophyton terrestre were significantly separated. The speciation of true dermatophytes resulted most likely from a very recent evolution by adaptation to parasitism. Among species used as o utgroups, the two emerging pathogens Pseudallescheria boydii (Scedospo rium apiospermum) and Scedosporium prolificans (Scedosporium inflatum) were shown to be closely related to each other.