Morphological and Molecular Genetic Analyses of the Genus Vischeria (Eustigmatophyceae, Ochrophyta) in the Algal Collection of Soil Science Institute

Four soil eustigmatophyte algal strains isolated from gray forest soils in Moscow and Tula regions of Russia and deposited in the Algal Collection of Soil Science Institute (ACSSI) were examined by morphological and molecular genetic methods. The strains were assigned to the genus Vischeria on evidence of 18S rRNA gene and ITS2 phylogeny. The strains were morphologically similar to V. magna. However, only one of them, ACSSI 026, clustered with the authentic strain SAG 2554, while the other strains formed a separate independent group. The taxonomy of the genus is problematic because its phylogenetic tree based on the 18S rRNA gene and ITS2 is unresolved, the variable regions V4–V5 and V8–V9 of the 18S rRNA gene are noninformative, and the compensatory base change (CBC) concept fails to work (the concept states that closely related species are distinct if even a single CBC occurs in conserved secondary structure regions of ITS2). The concept of species is presumably possible to develop for Eustigmatophyceae and the genus Vischeria in particular when a greater number of eustigmatophyte algal strains are isolated from various biotopes; plastid genes are used or the total plastid genome is deeply sequenced; and ultrastructural, physiological, and biochemical characteristics are studied in more detail.