The morphology of diatom siliceous is a primary basis for their species identification. This study aims to measure the range of morphological changes induced in the monoclonal cultures of Fragilaria radians strains 280 and A6 and Ulnaria danica strain BK17 by cultivation in the lab for a year or more. The scanning electron microscopy revealed that the number of abnormal valves increases during the first year of culture maintenance. Specific abnormalities observed include curved valves and apices, axial areas and rimoportulae shifted from their normal positions, disordered or otherwise abnormal striae, and various growths on the valves. Similar morphological abnormalities are known to occur in diatoms exposed to microtubule inhibitors. These results show the limits of morphological variance in studied species and could be used to estimate the effect of toxic agents in natural and experimental conditions.

Diatoms from the extreme cold habitats in northern areas of East Siberia are still poorly studied. Ecological significance of the lakes of the Pole of Cold of the Northern Hemisphere consists in their pristine environment characterized by special environmental factors, such as the long ice cover period, low temperatures, short vegetative period, low photosynthetically active radiation, deficiency of nutrients. Such water systems can thus be used as sensitive indicators of environmental changes. The diatom Ulnaria ulna (Nitzsch) Compere from the genus Ulnaria (Kutzing) Compere is wide-spread in fresh and brackish waters of the world, both in plankton and in benthos, which raises questions about the actual distribution of this species and the presence of cryptic species hidden under this name. In this study, monoclonal cultures of Ulnaria were isolated from epilithic micro-phytobenthos collected in Lake Labynkyr, located in the northern Pole of Cold region in the Sakha Republic (Yakutia), and were investigated in detail by light and scanning electron microscopy and phylogenetic analysis of the rbcL gene fragments. Cells in culture were able to attach to the substrate with mucilage strands secreted through the pore fields of both valves at one end of the cell. The results of the morphometric and phylogenetic analyses enabled to identify the isolated clones as Ulnaria pilum Kulikovskiy & Lange-Bertalot and showed that species morhoplogical variability is larger than originally described.

Silicon transporters (SIT) are the proteins, which capture silicic acid in the aquatic environment and direct it across the plasmalemma to the cytoplasm of diatoms. Diatoms utilize silicic acid to build species-specific ornamented exoskeletons and make a significant contribution to the global silica cycle, estimated at 240 ±40 Tmol a year. Recently SaSIT genes of the freshwater araphid pennate diatom Synedra acus subsp. radians are found to be present in the genome as a cluster of two structural genes (SaSIT-TD and SaSIT-TRI) encoding several concatenated copies of a SIT protein each. These structural genes could potentially be transformed into “mature” SIT proteins by means of posttranslational proteolytic cleavage. In the present study, we discovered three similar structural SuSIT genes in the genome of a closely related freshwater diatom Synedra ulna subsp. danica. Structural gene SuSIT1 is identical to structural gene SuSIT2, and the two are connected by a non-coding nucleotide DNA sequence. All the putative “mature” SITs contain conserved amino acid motifs, which are believed to be important in silicon transport. The data obtained suggest that the predicted “mature” SIT proteins may be the minimal units necessary for the transport of silicon is S. ulna subsp. danica. The comparative analysis of all available multi-SITs has allowed us to detect two conservative motifs YQXDXVYL and DXDID, located between the “mature” proteins. Aspartic acid-rich DXDID motif can, in our opinion, serve as a proteolysis site during the multi-SIT cleavage. The narrow distribution of the distances between CMLD and DXDID motifs can serve as additional evidence to the conservation of their function.

On-site measurement of methanethiol (CH3SH) was performed for three years on ships and cars near a pulp and paper plant standing on the shore of Lake Baikal in Siberia, Russia, to investigate the behavior and impact of atmospheric CH3SH emitted from a point source. Despite its strong odor, there are few reports on atmospheric CH3SH, while many investigations have been carried out on dimethyl sulfide (DMS). In this work, CH3SH and DMS were measured every 15 min by a recently developed automated instrument based on single column trapping/separation and chemiluminescence measurement. Hydrogen sulfide, sulfur dioxide and ozone were also measured simultaneously by individual instruments. Of these sulfur compounds, CH3SH was dominant and its concentration sometimes reached several tens of ppbv. The concentration of CH3SH was high at night, because of the lack of photodecomposition and local winds from the mountain to the lake. Such time variation was marked in the summer. The CH3SH level decreased significantly downwind, while decreases in concentrations of other compounds such as DMS and SO2 were relatively small. From these temporal and spatial variations, the behavior of CH3SH is described in this paper. The impact of CH3SH near the Siberian big sources is discussed with the presented data. (C) 2010 Elsevier Ltd. All rights reserved.

The planktonic diatoms, Asterionella formosa Kutz. and Synedra acus Hass., were cultivated in 96-well flat-bottom plastic plates with 100 mu L of medium per well. At regular time intervals, cells were counted using an inverted microscope. Typically, the number of cells per well increased over 10 days from 50-200 to >1000. The first growth inhibition experiments were successfully run at room temperature using natural illumination. However, for better control of the growth conditions, a special micro-incubator was manufactured. This device hosted two incubation plates and was equipped with Peltier elements for cooling below room temperature, and a small luminescent lamp. For automatic counting, two digital micro-photographs of each well were taken, first at a 0.2 msec exposure and the second at a 5 msec exposure. The images were treated by means Of custom software based on ImagePro to identify and count the diatom cells. Cultivation of diatoms on the micro-scale proved to be a convenient technique. Using this technique, we were able to study the effects of (2+) on A. formosa and Cu2+, Hg2+, Cd2+ and phenanthroline upon the rnercaptoethanol, Cu2+ oil A. formosa and Cu2+, Hg2+, Cd2+ and plienanthroline upon the growth of S. acus.

It is proposed that the conserved Cys-Met-Leu(I1e)-Asp [CML(I)D] motif of silicic acid transport proteins of diatom algae binds Zn2+ which, in its turn, takes part in binding and transport of silicic acid. We noticed a conservative motif CMLD in the amino acid sequences of silicic acid transport proteins (SITs) predicted from the published nucleotide sequences of the corresponding genes from Cylindrotheca fusformis Reimann et Lewin (Hildebrand et al. 1997, 1998), Phaeodactylum tricornutum Bohlin (Scala et al. 2002), Synedra acus Kutzing (Grachev et al. 2002), and Chaetoceros muelleri Lemmermann (Masyukova et al. 2004, Sherbakova et al. 2005). It was proposed that the functional groups of the C, M and D residues of this motif can form a binding site for Zn2', which is known to be necessary for the uptake of silicic acid by diatoms (Reuter & Morel 1981). According to our hypothesis, Zn2+ takes part in binding of silicic acid by SITs and, acting as a Lewis acid, facilitates nucleophilic attack of the silicon atom by either a second molecule of silicic acid, or, more probably, a functional group of SIT (Fig. I). In an accord with the hypothesis, Zn2+ inhibits the alkylation of cysteine