Small subunit ribosomal DNA sequence shows Paracoccidioides brasiliensis closely related to Blastomyces dermatitidis

The similarities of paracoccidioidomycosis and blastomycosis are highly sug gestive of a close relation of the two etiological agents. Whereas the agen t of the first disease is exclusively endemic in Latin America, the agent o f the latter one is endemic in North America and Africa. In symptomatic tra velers visiting both areas of endemicity, differentiation of the diseases m ight be impossible, even though therapy and prognosis for these two disease s differ significantly. In order to identify differences in the 18S rRNA ge ne (rDNA) for use as molecular diagnostic tools, we sequenced this gene fro m five isolates of Paracoccidioides brasiliensis and compared them to known sequences of other fungi. Neighbor-joining, maximum parsimony, and maximum likelihood analyses and, finally, the Kishino-Hasegawa test revealed that P. brasiliensis, Blastomyces dermatitidis, and Emmonsia parva are more clos ely related than Histoplasma capsulatum and B. dermatitidis, whose teleomor phic forms belong to one genus, Ajellomyces, In accordance with the work of other investigators who have used internal transcribed spacer and large su bunit rDNA sequences, our small subunit rDNA data show that the dimorphic f ungus P, brasiliensis must be grouped within the order Onygenales and is cl osely related to members of the family Onygenaceae, There are hints in the molecular phylogenetic analysis that the family Onygenaceae might be furthe r divided into two families. The subgroup that includes P. brasiliensis com prises all zoopathogenic species. The differences in the 18S rDNAs appear t o be too small to allow species identification of the members of the family Onygenaceae pathogenic for humans by use of target sequences within this g ene.