Yelena V. Likhoshway

The Distribution of Diatoms Near a Thermal Bar in Lake Baikal

Studies of the spatial distribution of suspended matter and of diatoms across a thermal bar in Lake Baikal revealed that waters sinking at the thermal bar front (2 km off-shore) move to the bottom along the underwater slope, and may be traced to a depth of at least 700 m, 5 km off-shore. The distributions of 11 diatom species across the thermal bar were significantly different, reflecting their different ecological requirements. Maximum concentrations of Asterionella formosa, Nitzschia acicularis, Aulacoseira islandica occur near the shore. The distribution of Stephanodiscus hantzschii, a species characteristic of the Selenga River, suggests that riverine waters penetrate far into the lake along its eastern shore. Another species typical of the Selenga River, Stephanodiscus minutulus, was found both near the shore, and in the surface waters of the open lake. Endemic spring baikalian diatoms Aulacoseira baicalensis and Cyclotella baicalensis were found at highest concentrations in the deep waters far off-shore, beyond the thermal bar. Another endemic diatom, the autumn species Cyclotella minuta was evenly distributed over the open lake at all depths. The data obtained shed new light on the dynamics of water masses near thermal bars, and on the ecology of the diatom species studied.

Novel fluorescent dyes based on oligopropylamines for the in vivo staining of eukaryotic unicellular algae

Weakly basic fluorescent dyes are used to visualize organelles within live cells due to their affinity to acidic subcellular organelles. In particular, they are used to stain the silica deposited in the silica deposition vesicles (SDVs) of diatoms during the course of their frustule synthesis. This study involved the synthesis of fluorescent dyes derived from oligopropylamines, compounds similar to those found in diatoms. The dyes were obtained by reacting oligopropylamines with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole. The reaction was realized using methylated oligopropylamines with two or three nitrogen atoms and yielded two novel fluorescent dyes: NBD-N2 and NBD-N3. The dyes appeared to be highly efficient in the in vivo staining of growing siliceous frustules of diatoms at concentrations at least 10 times lower than those required for staining with HCK-123. NBD-N3 also efficiently stained other subcellular vesicles of eukaryotic unicellular algae. NBD-N2 stained only growing diatom frustules, whereas NBD-N3 also stained various subcellular organelles of different eukaryotic unicellular algae. NBD-N2 and NBD-N3 were not removed from stained diatom frustules by drastic treatments with H(2)SO(4) and H(2)O(2). Fluorescent silica can also be obtained by its chemical precipitation in the presence of NBD-N2 and NBD-N3.

Silicon nanotechnologies of pigmented heterokonts

Many pigmented heterokonts are able to synthesize elements of their cell walls (the frustules) of dense biogenic silica. These include diatom algae, which occupy a significant place in the biosphere. The siliceous frustules of diatoms have species‐specific patterns of surface structures between 10 and a few hundred nanometers. The present review considers possible mechanisms of uptake of silicic acid from the aquatic environment, its transport across the plasmalemma, and intracellular transport and deposition of silica inside the specialized Silica Deposition Vesicle (SDV) where elements of the new frustule are formed. It is proposed that a complex of silicic acid with positively charged proteins silaffins and polypropylamines remains a homogeneous solution during the intracellular transport to SDV, where biogenic silica precipitates. The high density of the deposited biogenic silica may be due to removal of water from the SDV by aquaporins followed by syneresis—a process during which pore water is expelled from the network of the contracting gel. The pattern of aquaporins in the silicalemma, the membrane embracing the SDV, can determine the pattern of species‐specific siliceous nanostructures. BioEssays 30:328–337, 2008.

THE FRUSTULE STRUCTURE OF ORIGINAL MATERIAL OF AULACOSEIRA DISTANS (EHRENBERG) SIMONSEN

The original material from which Ehrenberg described Gallionella distans has been examined with light and electron microscopy with a view to understanding the morphology of a taxon that is now within the genus Aulacoseira and has a number of varieties. Aulacoseira distans has a distinctive heterovalvy, the “separation valves” that have no spines; areolae over the whole of the valve face; spines on the mantle edge are usually positioned between rows of areolae on the mantle which are in more or less straight rows; and a deep, thick ringleist with numerous rimoportulae against its inner side. Cells are found in short chains. This combination of characters does not match that in most published illustrations of A. distans and brings into question the taxonomic relationships of some of the published varieties. A lectotype has been chosen and deposted at BHU (the Ehrenberg collection at the Museum fur Naturkunde der Humboldt-Universitat in Berlin, and an isolectotype at BRM, (Bremerhaven).

Morphology and Identity of Aulacoseira italica and typification of Aulacoseira (Bacillariophyta)

Original material of Ehrenbergs from Santa Fiora (Tuscany, Italy) was examined to establish the identity of the diatom to which Ehrenberg gave the name Gaillonella italica. It was compared with other Ehrenberg material, notably from New England, and with numerous other samples, both fossil and recent, with a view to understanding the taxonomy of this species. Although Ehrenberg later discarded the name, it was validly published and we consider it synonymous with G. crenulata. However, despite the earlier publication of G. italica, G. crenulata remains the type of the name of the genus Aulacoseira. New observations on the rimoportulae and the velum together with recent illustrations of separation valves have been added to the features used to distinguish the species from others in the genus, of which, the most important, though hitherto neglected, is the curving of the pore rows to the left (sinistrorse). We draw attention to the fact that A. italica has often been confused with A. valida.

Controlled stabilisation of silicic acid below pH 9 using poly(1-vinylimidazole)

We show, for the first time, inhibition of silicic acid condensation over a wide range of pH, especially below 9 using certain molecular mass fractions of poly(1-vinylimidazole) (PVI). This is achieved by stabilisation of molybdate-active Si species, which are crucial to condensation and growth to form silica. The structure of the resulting composites depends on the molecular mass of the PVI chains. Long-chain macromolecules can “encapsulate” Si species giving rise to stable soluble complexes. Short PVI chains stimulate association of silica particles and at neutral pH precipitation occurs. Protonation of imidazole units in acidic pH results in dissolution of the precipitates. We believe that the results presented herein using PVI as a model system will help elucidate the mechanisms underpinning the molecular interactions between (bio)macromolecules and inorganic materials.

The Structure of Microbial Community and Degradation of Diatoms in the Deep Near-Bottom Layer of Lake Baikal

Insight into the role of bacteria in degradation of diatoms is important for understanding the factors and components of silica turnover in aquatic ecosystems. Using microscopic methods, it has been shown that the degree of diatom preservation and the numbers of diatom-associated bacteria in the surface layer of bottom sediments decrease with depth; in the near-bottom water layer, the majority of bacteria are associated with diatom cells, being located either on the cell surface or within the cell. The structure of microbial community in the near-bottom water layer has been characterized by pyrosequencing of the 16S rRNA gene, which has revealed 149 208 unique sequences. According to the results of metagenomic analysis, the community is dominated by representatives of Proteobacteria (41.9%), Actinobacteria (16%); then follow Acidobacteria (6.9%), Cyanobacteria (5%), Bacteroidetes (4.7%), Firmicutes (2.8%), Nitrospira (1.6%), and Verrucomicrobia (1%); other phylotypes account for less than 1% each. For 18.7% of the sequences, taxonomic identification has been possible only to the Bacteria domain level. Many bacteria identified to the genus level have close relatives occurring in other aquatic ecosystems and soils. The metagenome of the bacterial community from the near-bottom water layer also contains 16S rRNA gene sequences found in previously isolated bacterial strains possessing hydrolytic enzyme activity. These data show that potential degraders of diatoms occur among the vast variety of microorganisms in the near-bottom water of Lake Baikal.

A new subfamily LIP of the major intrinsic proteins

BackgroundProteins of the major intrinsic protein (MIP) family, or aquaporins, have been detected in almost all organisms. These proteins are important in cells and organisms because they allow for passive transmembrane transport of water and other small, uncharged polar molecules.ResultsWe compared the predicted amino acid sequences of 20 MIPs from several algae species of the phylum Heterokontophyta (Kingdom Chromista) with the sequences of MIPs from other organisms. Multiple sequence alignments revealed motifs that were homologous to functionally important NPA motifs and the so-called ar/R-selective filter of glyceroporins and aquaporins. The MIP sequences of the studied chromists fell into several clusters that belonged to different groups of MIPs from a wide variety of organisms from different Kingdoms. Two of these proteins belong to Plasma membrane intrinsic proteins (PIPs), four of them belong to GlpF-like intrinsic proteins (GIPs), and one of them belongs to a specific MIPE subfamily from green algae. Three proteins belong to the unclassified MIPs, two of which are of bacterial origin. Eight of the studied MIPs contain an NPM-motif in place of the second conserved NPA-motif typical of the majority of MIPs. The MIPs of heterokonts within all detected clusters can differ from other MIPs in the same cluster regarding the structure of the ar/R-selective filter and other generally conserved motifs.ConclusionsWe proposed placing nine MIPs from heterokonts into a new group, which we have named the LIPs (large intrinsic proteins). The possible substrate specificities of the studied MIPs are discussed.

Sub-Ice Microalgal and Bacterial Communities in Freshwater Lake Baikal, Russia

The sub-ice environment of Lake Baikal represents a special ecotope where strongly increasing microbial biomass causes an “ice-bloom” contributing therefore to the ecosystem functioning and global element turnover under low temperature in the world’s largest freshwater lake. In this work, we analyzed bacterial and microalgal communities and their succession in the sub-ice environment in March–April 2010–2012. It was found out that two dinoflagellate species (Gymnodinium baicalense var. minor and Peridinium baicalense Kisselew et Zwetkow) and four diatom species (Aulacoseira islandica, A. baicalensis, Synedra acus subsp. radians, and Synedra ulna) predominated in the microalgal communities. Interestingly, among all microalgae, the diatom A. islandica showed the highest number of physically attached bacterial cells (up to 67 ± 16 bacteria per alga). Bacterial communities analyzed with pyrosequencing of 16S rRNA gene fragments were diverse and represented by 161 genera. Phyla Proteobacteria, Verrucomicrobia, Actinobacteria, Acidobacteria, Bacteroidetes, and Cyanobacteria represented a core community independently on microalgal composition, although the relative abundance of these bacterial phyla strongly varied across sampling sites and time points; unique OTUs from other groups were rare.

CYCLOTELLA GRACILIS SP. NOV. FROM PLEISTOCENE MATERIAL OF LAKE BAIKAL, RUSSIA

Cyclotella gracilis sp. nov. is described from Pleistocene deposits of Lake Baikal. Valves are small (2–7 μm in diameter) and round. The similarity to other Cyclotella species (C. gordonensis and C. sibirica) is discussed and the differences from other common species in Lake Baikal (C. baicalensis and C. minuta) are shown.