Evolutionary Affinities of Heterobasidiomycetous Yeasts Estimated from 18S and 25S Ribosomal RNA Sequence Divergence

Abstract

Summary Phylogenetic relationships among heterobasidiomycetous yeasts, including anamorphic and teleomorphic taxa, have been compared from the sequence similarity of small (18S) and large (25S) subunit ribosomal RNA. Species examined were Cystofilobasidium capitatum, Filobasidiella neoformans, Filobasidium floriforme, Leucosporidium scottii, Malassezia furfur, M. pachydermatis, Phaffia rhodozyma, Rhodosporidium toruloides, Sporidiobolus johnsonii, Sterigmatosporidium polymorphum, Trichosporon beigelii, T. cutaneum and T. pullulans. The taxa cluster into three main groups. One group contains the nonteliospore forming genera Sterigmatosporidium, Filobasidiella, Filobasidium and the anamorphic species T. beigelii and T. cutaneum. The teliospore formers Leucosporidium, Rhodosporidium and Sporidiobolus, all of which have simple septal pores, cluster into a single group, despite the heterogeneity of carotenoid formation. By contrast, C. capitatum appears separate, not only from Rhodosporidium, but also from the Filobasidiaceae with which it shares a primitive dolipore septum. The uniqueness of the genus Malassezia among yeasts is confirmed, and one might predict from nucleotide sequence similarity that teleomorphs of those lipophilic organisms would form teliospores whereas Trichosporon beigelii and T. cutaneum appear related to the family Filobasidiaceae.