Species distinction of the ascomycetous heterothallic yeast-like fungus Stephanoascus ciferrii complex: description of Candida allociferrii sp. nov. and reinstatement of Candida mucifera Kocková-Kratochvílová et Sláviková.

The nucleotide sequences of the 18S rRNA gene (rDNA) from nine strains of the heterothallic ascomycetous Stephanoascus ciferrii complex were determined and the strains were separated into three groups according to their sequences. 18S rDNA sequences were identical within the same group. In group A the 18S rDNA sequences had no introns; in group B there was one group I intron, Sc1506-1 at position 1506; and in group C there were two group I introns, Sc943 at position 943 and Sc1506-2 at position 1506. Sc1506-1 and Sc1506-2 at position 1506 exhibited 19 base differences but were very similar. Therefore, it is suggested that these introns existed in the common ancestor of groups B and C, and that they were vertically inherited. DNA similarity values showed that the strains within the same group were of identical species. Group B included the isotype strains of Stephanoascus ciferrii and the type strains of Candida ciferrii and Sporothrix catenata; this confirmed that group B strains correspond to Stephanoascus ciferrii and that Candida ciferrii and Sporothrix catenata are synonyms of Stephanoascus ciferrii. The single member of group C, strain IFO 10918T, corresponds to the type strain of Candida mucifera and was independent of the other tested strains. Thus, Candida mucifera should be regarded as an independent species from Stephanoascus ciferrii. It is suggested that group A strains might comprise a new Stephanoascus species, but since group A strains could not form asci by themselves in this study they are described as a new species for which the name Candida allociferrii sp. nov. (type strain IFO 10194T) is proposed.