O. I. Belykh

Comparative analysis of biodiversity in the planktonic and biofilm bacterial communities in Lake Baikal

Bacterial communities of the water and the biofilm formed during five years on an artificial substrate in Lake Baikal were studied by the pyrosequencing of 16S rRNA gene fragments; taxonomic diversity of bacterial communities and differences in their structure were revealed. The biofilm community contained mainly representatives of three phyla: Cyanobacteria, Bacteroidetes, and Proteobacteria; the amounts of other groups were within 1%. Bacterial community of the plankton was more heterogeneous; along with the dominant phyla (Bacteroidetes, Actinobacteria, and Proteobacteria) 15% of the members were of the other phyla. The use of pyrosequencing allowed to reveal 35 bacterial phyla in Lake Baikal, some of which were identified for the first time; moreover, minor groups of microorganisms (including only several sequences), which were not earlier determined by other molecular methods were found.

Presence and genetic diversity of microcystin-producing cyanobacteria (Anabaena and Microcystis) in Lake Kotokel (Russia, Lake Baikal Region)

A survey was conducted for the presence of cyanobacteria toxins in Lake Kotokel due to a few cases of Haff disease registered in 2008–2009 caused by consumption of fish from Lake Kotokel, and wildlife mortality including large fish kill. The aims of this study were to determine what cyanotoxins (if any) were present in the lake, to describe phytoplankton composition including morphology, density, and species diversity of cyanobacteria, as well as to evaluate the trophic state of the lake. Samples were collected from both nearshore and central sites in August of 2009. Aphanocapsa holsatica dominated the phytoplankton. The presence of toxigenic genotypes of Microcystis spp. and Anabaena lemmermannii was detected by sequencing of PCR-amplified aminotransferase domain of microcystin synthetase gene. LR, RR, and YR microcystin (MC) variants were detected with liquid chromatography-UV mass spectrometry. The data do not shed light on the etiology of Haff disease in Lake Kotokel region, nevertheless taking into account the recreational importance of the lake and its direct connection to Lake Baikal, a necessity to monitor cyanobacteria in these water bodies is evident. This is the first report on simultaneous detection of MC-producing genotypes and MCs in the Lake Baikal region.

A eukaryotic alga from picoplankton of Lake Baikal: morphology, ultrastructure and rDNA sequence data

An eukaryotic alga (strain BAC 9708) from the picoplankton of Lake Baikal (Eastern Siberia) has been cultivated in order to investigate its morphology, ultrastructure, growth requirements, pigment composition and nuclear-encoded 18S and chloroplast-encoded 16S rDNA sequences. Cells of strain BAC 9708 contain a nucleus, a single chloroplast without a pyrenoid, one mitochondrion, a poorly visible dictyosome, a large vacuole and a cell wall with an outer sporopollenin-containing layer. Ellipsoidal cells, 1.5–2.0 × 1.0–1.5 μm in size, propagate usually by two, or infrequently by four autospores. Sequence analysis of nuclear-encoded rDNA showed that all 581 nucleotides of the 5′-end of the 18S rDNA were identical to that of Choricystis minor (Skuja) Fott (Chlorococcales, Chlorophyta) obtained earlier (Krienitz et al., 1996). The chloroplast-encoded rDNA sequence of this strain showed identity with one of three chloroplast sequences, selected by PCR-amplification with 16S rDNA specific primers from total picoplanktonic DNA, obtained previously.

Analysis of Bacterial Communities of Two Lake Baikal Endemic Sponge Species

Bacterial diversity of two Lake Baikal endemic sponges characterized by different life forms, branching Lubomirskia baicalensis and encrusting Baikalospongia sp., was studied using 454 pyrosequencing of the 16S rRNA gene fragments. In the communities associated with L. baicalensis and Baikalospongia sp., 426 and 428 OTUs, respectively, were identified. In microbial associations of these sponges, 24 bacterial phyla with predominance of Bacteroidetes, Proteobacteria, and Actinobacteria were identified. Analysis of the taxonomic composition of bacterial communities of the sponges was carried out by searching the dominant phylotypes within the clusters of phylum level. Comparison of bacterial associations of the sponges with Lake Baikal bacterioplankton revealed both the shared OTUs and the unique ones characteristic of the studied species.

Identification of toxigenic Cyanobacteria of the genus Microcystis in the Curonian Lagoon (Baltic Sea)

In 2002–2008, seasonal (April–November) monitoring of the phytoplankton in the Russian part of the Curonian Lagoon at five fixed sites was performed. A total of 91 Cyanobacteria, 100 Bacillariophyta, 280 Chlorophyta, 21 Cryptophyta, and 24 Dinophyta species were found. Six potentially toxic species of cyanobacteria: Aphanizomenon flos-aquae, Anabaena sp., Microcystis aeruginosa, M. viridis, M. wesenbergii, and Planktothrix agardhii dominated the phytoplankton biomass and caused water blooms. The seasonal average phytoplankton biomass ranged from 30 to 137 g/m3. The cyanobacteria’s biomass varied from 10 to 113 g/m3 forming 30–82% of the total with a mean of 50%. With the aid of genetic markers (microcystin (mcy) and nodularin synthetases), six variants of the microcystin-producing gene mcyE from the genus Microcystis were identified. Due to the intensive and lengthy blooms of potentially toxic and toxigenic cyanobacteria, the environmental conditions in the Curonian Lagoon appear unfavorable. The water should be monitored for cyanotoxins with analytical methods in order to determine if the area is safe for recreational use.

Ecological development and genetic diversity of Microcystis aeruginosa from artificial reservoir in Russia.

Microcystis aeruginosa is a well-known Cyanobacterium responsible for the formation of toxic water blooms around the world. Shallow, warm, and eutrophic reservoirs provide the most favourable conditions for M. aeruginosa development. Numerous studies have been devoted to this species, but there still is a necessity to develop additional approaches for the monitoring of cyanobacteria in reservoirs. In this study, M. aeruginosa in the water column of a hypereutrophic Siberian reservoir was investigated by fluorescence, light, and electron microscopy as well as genetic analysis using a mcyE marker. Here, we demonstrate the genetic diversity and features of the fluorescence spectra for different ecotypes of this species. We suggest that a fluorescence approach can be used to identify M. aeruginosa in a natural environment in order to increase the effectiveness of ecological monitoring and water quality evaluation.

Diversity of the major capsid genes (g23) of T4-like bacteriophages in the eutrophic Lake Kotokel in East Siberia, Russia.

Numerous studies revealed high diversity of T4-like bacteriophages in various environments, but so far, little is known about T4-like virus diversity in freshwater bodies, particularly in eutrophic lakes. The present study was aimed at elucidating molecular diversity of T4-like bacteriophages in eutrophic Lake Kotokel located near Lake Baikal by partial sequencing of the major capsid genes (g23) of T4-like bacteriophages. The majority of g23 fragments from Lake Kotokel were most similar to those from freshwater lakes and paddy fields. Despite the proximity and direct water connection between Lake Kotokel and Lake Baikal, g23 sequence assemblages from two lakes were different. UniFrac analysis showed that uncultured T4-like viruses from Lake Kotokel tended to cluster with those from the distant lake of the same trophic status. This fact suggested that the trophic conditions affected the formation of viral populations, particularly of T4-like viruses, in freshwater environments.

Identification of Cyanobacterial Producers of Shellfish Paralytic Toxins in Lake Baikal and Reservoirs of the Angara River

The goal of the present work was to search for PST� producing cyanobacteria in Lake Baikal and reservoirs of the Angara River using a marker for the polyketide synthase gene stxA and to detect saxitoxin and its ana� logues by enzymelinked immunosorbent assay (ELISA) and mass spectrometry. Samples from Lake Baikal were collected in August 2010 in the coastal zone of the Barguzin and Kurkut Bays (Maloe More Strait). Samples were taken from the Irkutsk reservoir (near Patrony village), Bratsk res� ervoir (near NovoDolonovo village), and UstIlimsk reservoir (near Zheleznodorozhnik settlement) in July 2010. Plankton was sampled with a Ruttner sampler from 1�m depth and with an Apstein plankton net by filtration of the upper 1.5�m water layer. The bottle samples were used for qualitative and quantitative assessment of cyanobacteria as described previously (5). Total DNA was extracted from net samples fixed with 70% ethanol using the DNAsorb kit (InterLab� Servis, Russia). The

Role of phytoplankton size distribution in lake ecosystems revealed by a comparison of whole plankton community structure between Lake Baikal and Lake Biwa

The influence of the size distribution of phytoplankton on changes in the planktonic food web structures with eutrophication was examined using natural planktonic communities in two world-famous lakes: Lake Baikal and Lake Biwa. The size distribution of phytoplankton and the ratio of heterotrophic to autotrophic biomass (H/A ratio), indicating the balance between primary production and its consumption, were investigated in the lakes of different trophic status. The results revealed that microphytoplankton (>20μm) in mesotrophic Lake Biwa, and picophytoplankton (<2μm) or nanophytoplankton (2–20μm) in oligotrophic Lake Baikal, comprised the highest proportion of the total phytoplankton biomass. The H/A ratio was lower in Lake Biwa (<1) than in Lake Baikal (>1). The low H/A ratio in Lake Biwa appeared to be the consequence of the lack of consumption of the more abundant microphytoplankton, which were inferior competitors in nutrient uptake under oligotrophic conditions but less vulnerable to grazing. As a result, unconsumed microphytoplankton accumulated in the water column, decreasing the H/A ratio in Lake Biwa. Our results showed that food web structure and energy flow in planktonic communities were greatly influenced by the size distribution of phytoplankton, in conjunction with bottom-up (nutrient uptake) and top-down (grazing) effects at the trophic level of primary producers.

Stratified distribution of nutrients and extremophile biota within freshwater ice covering the surface of Lake Baikal

Biological entities and gradients of selected chemicals within the seemingly barren ice layers covering Lake Baikal were investigated. Ice cores 40–68 cm long were obtained from inshore and offshore sites of Southern Lake Baikal during the cold period of a year (March–April) in 2007 and 2008. In microscopic observations of the melted ice, both algae and bacteria were found in considerable numbers (>103 cells/L and >104 cells/ml, respectively). Among all organisms found, diatom was generally the most predominant taxon in the ice. Interestingly, both planktonic and benthic algae were present in considerable numbers (2–4×104 cells/L). Dominant phototrophic picoplankton were comprised of small green algae of various taxa and cyanobacteria of Synechococcus and Cyanobium. The bacterial community consisted mostly of short rod and cocci cells, either free-living or aggregated. Large numbers of yeast-like cells and actinomycete mycelium were also observed. Concentrations of silica, phosphorus, and nitrate were low by an order of magnitude where biota was abundant. The profile of the ice could be interpreted as vertical stratification of nutrients and biomass due to biological activities. Therefore, the organisms in the ice were regarded to maintain high activity while thriving under freezing conditions. Based on the results, it was concluded that the freshwater ice covering the surface of Lake Baikal is considerably populated by extremophilic microorganisms that actively metabolize and form a detritus food chain in the unique large freshwater ecosystem of Lake Baikal.