Ye. V. Likhoshway

Conserved motif CMLD in silicic acid transport proteins of diatoms

Sequenced fragments of genes coding for silicon transporters (SITs) were analyzed for diatoms of evolutionarily distant classes (centric Chaetoceros muelleri Lemmermann, pennate araphid Synedra acus Kützing, pennate raphid Phaeodactylum tricornutum Bohlin, and pennate Cylindrotheca fusiformis Reimann et Lewin with a keeled raphe system). SITs were found to contain a conserved motif, CMLD. Hydropathy profiles showed that the motif CMLD is between two transmembrane domains lacking Lys and Arg, and the domains were consequently assumed to play a role in the formation of a channel mediating silicic acid transport. The motif CMLD proved to be rare. Since Zn2+ is necessary for silica incorporation into diatom cells, a hypothesis was advanced that the motif CMLD acts as a Zn-binding site. Diatom growth suppression was observed in the presence of the alkylating agent N-iodoacetylamidoethyl-1-aminonaphthalene-5-sulfonic acid (AEDANS), which does not penetrate into the cell. Cys of the motif CMLD was assumed to act as a target for AEDANS. Zinc ions inhibited Cys alkylation in the synthetic peptide NCMLDY, testifying to the above hypothesis.

Chloroplast structure of diatoms of different classes

The diversity of chloroplast forms, and their number and cellular location, as well as pyrenoid structure, distinguishes diatoms from other groups of heterokont algae. The fine chloroplast structure is considered to be informative for taxonomic and phylogenetic studies of diatoms. Six species of diatoms belonging to different classes have been examined with transmission electron microscopy. New data on the chloroplast structure have been obtained. Characteristics of the pyrenoid ultrastructure of diatoms belonging to various phylogenetic clades have been defined more precisely. The results specify the ultrastructure of pyrenoids for different phylogenetic clades of diatoms and contribute to the previously obtained data.

Aberration of morphogenesis of siliceous frustule elements of the diatom Synedra acus in the presence of germanic acid.

Addition of germanic acid into the culture medium of the diatom Synedra acus subsp. radians (Kutz.) Skabitsch. had nearly no influence on the culture growth at the Ge/Si molar ratio 0.01, but stopped it at ratios 0.05 and higher. It was shown by mass-spectrometry that at the Ge/Si ratio 0.01 germanium was incorporated in both the cytoplasm and siliceous valves, whereas at Ge/Si 0.05 it was incorporated into the cytoplasm but almost failed to accumulate in the valves. At Ge/Si 0.1 germanium was accumulated in the cytoplasm, but its incorporation into the valves terminated. Studies on the cell morphology by light, epifluorescence, and transmission electron microscopy showed that high concentrations of germanic acid induced disorders in morphogenesis of the siliceous frustule and accumulation of large rhodamine-stainable electron-dense inclusions. Model chemical experiments with over-saturated solutions of silicic acid in the presence of polyallylamine revealed that addition of 5% germanic acid considerably accelerated coagulation of silica. Hence, the toxic effect of germanic acid on diatoms could be caused by changes in coagulation of silica.

Chrysophycean cysts (stomatocysts) from Lake Baikal and Irkutsk Reservoir, Siberia

Chrysophycean cysts (stomatocysts, statospores) from Lake Baikal and Irkutsk Reservoir, Siberia, Russia have been investigated by means of scanning electron microscopy for the first time. The paper contains descriptions and illustrations of 7 particularly distinctive forms. Five of the cyst types described here are new to the literature. Two are very similar to cysts previously described from lake sediments in North America, but differ in details of surface ornamentation and cyst collar construction.

Fine structure of the velum and girdle bands in Aulacoseira baicalensis

The fine structure of Aulacoseira (Melosird) baicalensis frustules has been studied by means of scanning and transmission electron microscopy. It appears that the form of the suture spines is conservative. Areolae are of two types. Type 1 areolae are loculate and are covered internally with a velum, with an additional finely perforate membrane, which is bell-shaped. Areolae of type 2 are laminar (non-loculate) with vela of the vola and rota types and do not have fine membranes, or have only minute ones. Intermediate forms are also present. The fine structure of the copulae has been investigated: they are perforated by fine pores (20–40 nm in diameter) in regular rows.

Taxonomic characterization of the microorganisms associated with the cultivable diatom Synedra acus from Lake Baikal

Determination of the taxonomic position of microorganisms associated with diatoms was carried out using microscopic, microbiological, and phylogenetic methods. Examination of the cultures of the fresh-water diatom Synedra acus grown in Lake Baikal water by epifluorescence and electron microscopy revealed that bacterial cells colonized the mucilage surrounding the cells of living microalgae and their cell surfaces and penetrate into the frustules of dead diatoms. A total of 13 strains of heterotrophic bacteria were isolated in pure cultures and described. Based on the results of analysis of their morphological, physiological, and biochemical properties, as well as on data obtained by 16S rRNA gene analysis, the following strains were identified to the species level: Sphingomonas sp., Variovorax paradoxus, Pseudomonas fluorescens, Microbacterium trichothecenolyticum, Rhodococcus sp., Caulobacter vibrioides, and Brevundimonas vesicularis.

VALVE MORPHOGENESIS IN AN ARAPHID DIATOM SYNEDRA ACUS SUBSP. RADIANS

Valve morphogenesis stages in the araphid Synedra acus subsp. radians (Kütz.) Skabitch. were studied using of the light, fluorescent and electron microscopes. The most interesting and complete results were obtained with transmission electron microscope (TEM). Morphogenesis begins by the formation of a thin silica strand (sternum) with little branches (future virgae). Virgae begin to grow as semi-transparent siliceous branches which often consist of two parts. Later, the distance between growing virgae are fuse by wimines from the sternum to the edge of valve and then areolae are formed into striae. The rimoportula and apical pore field start to form at an early stage of valve formation. In the beginning, the forming rimoportula looks like a loop of silica filament which often substitutes for an areola of the apical areola row. After the mantle begins to form, apical pore fields start to grow as series of small spines which subsequently evolve into ribs separating rows of porae. At the end of morphogenesis, the valve becomes thicker and attains the mature size and outline.

Similarity of structure of taxonomic bacterial communities in the photic layer of Lake Baikal’s three basins differing in spring phytoplankton composition and abundance

Pyrosequencing of amplicons V3-V4 of the 16S rRNA gene of 30 samples from the photic layer across the three basins of Lake Baikal has revealed 44 958 sequences of the domain Bacteria. The most representative phylums among all classified sequences in the samples were Actinobacteria, Bacteroidetes, Verrucomicrobia, Proteobacteria, Acidobacteria, and Cyanobacteria. As much as 38.5% of the total number of sequences has been determined to the level of genus. The taxonomic composition of bacterial communities was similar regardless of some differences in the composition and abundance of spring phytoplankton. Closely related or identical sequences of bacteria inhabiting the epilimnion of other lakes worldwide have been discovered for most sequences. This confirms the similarity of microbial communities in freshwater ecosystems.

Sequencing of the complete genome of an araphid pennate diatom Synedra acus subsp. radians from Lake Baikal

High-throughput method of sequencing was applied to determine the complete nucleotide sequence of an araphid pennate diatom Synedra acus subsp. radians from Lake Baikal (East Siberia). The assembled genome has a total length of 98 Mbp, the mean coverage is 33x. Structure-functional annotation of the genome was performed.

Detection of the silicic acid transport protein in the freshwater diatom Synedra acus by immunoblotting and immunoelectron microscopy.

295 Silicic acid transport proteins, or silicon transporters (SITs), ensure the key function of Bacillariophyta—the ability to capture silicic acid from the environment and transport it into cells for forming new silica frustules [1]. Silica cycle is one of the most large-scale processes in the biosphere [2]. Progress in understanding the mechanism of silica transport is restrained by the fact that individual SIT proteins have not been isolated thus far, and their location in the cell remains obscure.