System. Appl. Microbiol. 15, 250-258 (1992) © Gustav Fischer Verlag, StuttgartlNew York Evolution of Basidiomycetous Yeasts as Deduced from Small Ribosomal Subunit RNA Sequences YVES VAN DE PEER \ LYDIA HENDRIKS \ ANNE GORIS \ JEAN-MARC NEEFSI, MARC VANCANNEYT 2 , KAREL KERSTERS 2 , JEAN-FRANCOIS BERNy 3 , GREGOIRE L. HENNEBERT 3 , and RUPERT DE WACHTER h 1 Departement Biochemie, Universiteit Antwerpen (VIA), 2610 Antwerpen, Belgium 2 Laboratorium voor Microbiologie, Rijksuniversiteit Gent, 9000 Gent, Belgium 3 Mycotheque de l'Universite Catholique de Louvain, 1348 Louvain-la-Neuve, Belgium Received July 3, 1991 Summary Complete small ribosomal subunit RNA sequences were used to infer the relationship between several basidiomycetous yeasts, and to resolve the evolutionary position of the basidiomycetes among the fungi. The sequences were determined for Rhodosporidium torula ides (anamorph Rhodotorula glutinis), Filobasidiella neoformans (anamorph Cryptococcus neoformans), Trichosporon cutaneum, Bullera alba and Sporobolomyces roseus. The sequence of Leucosporidium scottii (anamorph formerly named Candida scottii) srRNA has already been published previously (Hendriks et aI., J. Mol. Evol. 32, 167-177 (1991)). Using a tree construction program based on a distance matrix, a phylogenetic tree was constructed for all hitherto known fungal srRNA sequences, oomycetes and slime moulds not included. It showed the ascomycetes and the basidiomycetes to be sister groups, probably evolved from a zygomycete-like ancestor and diverged from each other about 840 Myr ago. Among the basidiomycetes, two clearly distinct groups can be recognized, one formed by the teliospore forming species (Rhodosporidium toruloides and Leucos- poridium scottii), and the asexual yeast Sporobolomyces roseus, and the other formed by the non- teliospore forming species Filobasidiella neoformans and the asexual yeasts Bullera alba and Trichosporon cutaneum. Key words: Small ribosomal subunit RNA - Molecular evolution - Fungi - Basidiomycetous yeast - Phylogeny of yeasts Introduction Small ribosomal subunit RNA (further abbreviated as srRNA) sequences have been used extensively to study phylogenetic relationships among all sorts of organisms, varying from eubacteria (Woese, 1987) to archae bacteria (Achenbach-Richter et al., 1988; Woese and Olsen, 1986) and eukaryotes (Hendriks et al., 1988; Field et al., 1988; Sogin, 1989; Lake, 1990; Hendriks et al., 1991a). srRNA genes are universal and apparently do not undergo lateral gene transfer, while srRNAs are structurally and function- ally conserved. Also, due to the improvement of DNA and * Corresponding author Abbreviations: srRNA = small ribosomal subunit RNA; IrRNA = large ribosomal subunit RNA; kb = kilo bases RNA sequencing techniques, the determination of the complete or nearly complete nucleotide sequence of a ribosomal RNA is relatively straightforward. This has re- sulted in a large srRNA database, which presently com- prises about 450 sequences (Neefs et al., 1991). Up to now, the complete (or nearly complete) sequences of 26 fungal species (oomycetes and slime moulds not included) have been published. This set is listed in Table 1 and in- cludes 1 chytridiomycete, 1 zygomycete, 22 ascomycetes, 1 basidiomycete, and Pneumocystis carinii whose exact taxonomic status still remains unknown. In order to sup- plement and equilibrate the number of srRNAs for the higher fungi, we determined the complete srRNA se- quences of 5 basidiomycetous yeasts, viz. Rhodospori-