Abstract. Microalgae culture collections enable the practical use of the products of their metabolism and provide an overview of the morphological, genetic and physiological diversity known in nature. However, despite the fact that diatoms are a unique object, a little number of species is maintained in culture in world collections compared to their huge diversity. The Department of Cell Ultrastructure of the Limnological Institute of the Siberian Branch of the Russian Academy of Sciences (LIN SB RAS) has created a collection of monoclonal cultures of diatoms isolated from different regions of Lake Baikal and other water bodies. Currently, the collection is represented by 144 strains of planktonic and benthic diatoms belonging to 20 species. Regularly reseeded cultures are used to solve a number of problems related to ecology, taxonomy, cell biology, molecular genetic research, as well as for use in biotechnology.

Abstract. Ulnaria a us is a cosmopolitan freshwater diatom. As a rule, diatom populations represent a combination of different genotypes. In early study, using a fragment of the rbcL gene of U. acus strains isolated from geographically distant regions, no significant genetic differences were found in the populations of this species. In this paper, we analyzed 41 strains isolated from different regions of Eurasia. Based on the analysis of the 18S rRNA gene fragment, it was shown that all strains form a single clade consisting of U. acus. Phylogenetic analysis of cox1 genes revealed that Eurasian strains of U. acus form three clades. Strains of U. acus from Lake Ritsa (Abkhazia) and Lake Matano (Indonesia) are not heterogeneous. Strains of U. acus isolated from Lake Baikal (Russia) and the r. Erdre (France) contained two clades and we can suggest that the genetic structure of the populations of this species is heterogeneous. All studied populations are conspecific taking into account their sexual compatibility of at least two generations.

Algal-bacterial associations were studied in unialgal xenic cultures of Synedra acus subsp. radians, Asterionella formosa and Fragillaria crotonensis planktonic diatoms from Lake Baikal, using epifluorescent and scanning electron microscopy. It was found that rod- and ovoid-shaped bacteria colonized cell walls of diatoms. Cloning and sequencing of fragments of 16S rRNA gene in diatom cultures revealed members of Gammaproteobacteria (Pseudomonas sp.), Betaproteobacteria (Janthinobacterium sp., Hydrogenophaga sp., Methylophilus sp.), Bacteroidetes (Flavobacterium sp., Pedobacter sp.), and Acinobacteria (Nocardioides sp.).

The existence of the cluster of duplicated sit silicon transporter genes in the chromosome of the diatom Synedra acus subsp. radians was shown for the first time. Earlier, the localization of sit genes in the same chromosome and cluster formation caused by gene duplication was shown only for the marine raphid pennate diatom P. tricornutum. Only non-clustered sit genes were found in the genomes of other diatoms. It is reasonable to assume that sit tandem (sit-td) and sit triplet (sit-tri) genes of S. acus subsp. radians occurred as a result of gene duplication followed by divergence of gene copies.