Isolation of a divergent strain of Candida saitoana from the Anyui mummy of a steppe bison (Bison priscus)

Abstract

Yeasts are a traditional model for investigation of eukaryotic genetics. Yeasts are also a convenient model for developing the principles of phylogenetic classification and the species concept due to the com� paratively small size of the group and the previously accumulated knowledge on both the phenotypic and molecular biological characteristics of yeast species. The main criteria for classification of yeast species have initially been morphological, with subsequent investigation of their physiological characteristics. The present stage, while considering all accumulated knowledge, is based on the application of molecular biological techniques, primarily, the analysis of con� servative rDNA regions. Until recently, the reference point for establishing the criterion of a phylogenetic species in yeasts has been the percentage of differences in the ribosomal genes, more specifically, in the D1/D2 domains of the 26S (LSU) rDNA [1]. Quite recently, another rDNA region, ITS, was chosen as such a universal barcode marker for the whole king� dom of Fungi [2]. However, a large amount of data indicates that in some cases, including yeasts, inde� pendent application of these two regions is not always applicable, so it is necessary to use them jointly [3]. Moreover, the level of differences in the ribosomal genes for differentiation between yeast species is being discussed [4]. It is impossible to solve this problem without taking into account all the possible deviations from the type strains, which are stored in collections as “standard” strains. The discovery of genetically diver� gent strains makes it possible to specify the phyloge� netic boundaries of the species, and also contributes to development of the understanding that a phylogenetic species is not something discrete; slight deviations are always possible, and their level is to be studied in the future. In 2012, in the course of the investigation of the yeasts associated with the Pleistocene bison (steppe bison) mummy found recently in permafrost in the lower reach of Anyui River (Chukotka, Russia), the strain Candida saitoana VKPM Y�3988 was isolated, which had substantially divergent rDNA nucleotide sequences, as well as certain specific phenotypic fea� tures. The strain was isolated from the wool sampled from the surface of the carcass. Its identification was carried out by analyzing the nucleotide sequences of