Molecular phylogenetics of the genus trichosporon inferred from mitochondrial cytochrome B gene sequences

Abstract

Mitochondrial cytochrome b (cyt b) genes of 42 strains representing 23 species of the genus Trichosporon were partially sequenced to determine their molecular phylogenetic relationships. Almost half of the 22 strains investigated (from 11 different species) contained introns in their sequences. Analysis of a 396-bp coding sequence from each strain of Trichosporon under investigation showed a total of 141 (35.6%) variable nucleotide sites. A phylogenetic tree based on the cyt b gene sequences revealed that all species of Trichosporon except Trichosporon domesticum and Trichosporon montevideense had species-specific cyt b genes. Trichosporon sp. strain CBS 5581 was identified as Trichosporon pullulans, and one clinical isolate, IFM 48794, was identified as Trichosporon faecale. Analysis of 132-bp deduced amino acid sequences showed a total of 34 (25.75%) variable amino acid sites. T. domesticum and T. montevideense, Trichosporon asahii and Trichosporon asteroides, and Trichosporon gracile and Trichosporon guehoae had identical amino acid sequences. A phylogenetic tree constructed with the ascomycetes Saccharomyces douglasii and Candida glabrata taken as outgroup species and including representative species from closely related genera species of Trichosporon clustered with other basidiomycetous yeasts that contain xylose in their cell wall compositions. These results indicate the effectiveness of mitochondrial cyt b gene sequences for both species identification and the phylogenetic analysis of Trichosporon species.

FIG. 1.

Comparison of the deduced amino acid sequences encoded by the cyt b genes of species of the genus Trichosporon. Dots, amino acids that are identical to those of T. aquatile. Arrows indicate positions of introns.

FIG. 2.

Phylogenetic tree based on the nucleotide sequences of the cyt b gene. The tree was constructed by using UPGMA. Abbreviations for species names are shown in Fig. 1, and numbers shown are IFM strain numbers (our culture collections) (Table 1). T, type strain. Bar, number of nucleotide substitutions per nucleotide site.

FIG. 3.

Phylogenetic tree based on the deduced amino acid sequences encoded by the cyt b gene. The tree was constructed by using UPGMA. Abbreviations for species names are shown in Fig. 1, and numbers shown are IFM strain numbers (our culture collections) (Table 1). T, type strain.

FIG. 4.

Phylogenetic trees based on nucleotide sequences of cyt b genes. Trees were constructed by using the NJ, ML, and MP methods.