A. S. Gladkikh

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.

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 cyanobacterial species and phylotypes in biofilms from the littoral zone of Lake Baikal.

The majority of naturally occurring biofilms contain numerous microorganisms that have not yet been cultured. Additionally, there is little information available regarding the genetic structure and species diversity of these communities. Therefore, we characterised the species diversity, structure and metagenome of biofilms grown on stones and steel plates in the littoral zone of Lake Baikal (East Siberia, Russia) by applying three different approaches. First, light microscopy enabled identification of the species diversity of biofilm-forming cyanobacteria on different substrates with the dominance of Rivularia rufescens, Tolypothrix limbata, Chamaesiphon fuscus, Ch. subglobosus, and Heteroleibleinia pusilla. Additionally, scanning electron microscopy was used to show the spatial structure of biofilms. Finally, sequence analysis of 30,660 16S rRNA clones indicated a high diversity within the biofilm communities, with the majority of the microbes being closely related to Cyanobacteria (8–46% sequences), Proteobacteria (14–43%), and Bacteroidetes (10–41%). Rivularia sp., Pseudanabaena sp., and Chamaesiphon spp. were the dominant cyanobacterial phylotypes.

Saxitoxin-Producing cyanobacteria in Lake Baikal

Cyanobacteria containing neurotoxic saxitoxin synthesis genes were found in the coastal zone of Lake Baikal near the village of Turka for the first time. Phylogenetic analysis showed that the sequences of saxitoxin synthesis genes belong to the genus Anabaena Bory. Saxitoxin concentration in the water according to ELISA was 1.93 ± 0.64 mg/L. The genetic and taxonomic composition of the bacterial community of the central part of Lake Baikal was characterized using 16S rRNA gene pyrosequencing. It was established that the phylum Cyanobacteria dominated in the composition of summer bacterioplankton in both littoral and pelagic zones of the lake, but higher species diversity was found in the plankton of littoral zone.

Nitrogen-fixing cyanobacterium Trichormus variabilis of the Lake Baikal phytoplankton

A new filamentous cyanobacterial strain BAC 9610 was isolated from the lake Baikal pelagial. Data obtained by light, scanning, and transmission electron microscopy, along with 16S rRNA gene sequence analysis, allowed the bacterium identification as Trichormus variabilis, previously known as Anabaena variabilis. Trichormus is a cyanobacterial genus not presented in the list of Baikal plankton algae; A. variabilis also hasn’t been previously detected in Baikal phytoplankton. T. variabilis nitrogen fixation ability was demonstrated. The gene responsible for nitrogen fixation, nifH, was identified by PCR and was partially sequenced. No hepatotoxin synthesis genes were revealed in the strain.

Identification of toxic Cyanobacteria in Lake Baikal

Cyanobacteria of the genera Anabaena and Microcystis, containing genes for the synthesis of-microcystins (hepatotoxic cyanotoxins) were found for the first time in the coastal zone of Lake Baikal near-the village of Turka, where a tourism and recreational complex were constructed. According to the enzyme-immunoassay, microcystin concentration in water was 0.17 ± 0.01 µg/L. Using 16S rRNA gene pyrosequencing, we found 3936 sequences in the eubacterial community of central basin of Lake Baikal. The summer bacterioplankton in both littoral and pelagic areas of the lake was dominated by the phylum Cyanobacteria, whereas a higher diversity of cyanobacteria was recorded in the plankton of the littoral zone. Moreover, the-potentially toxic Anabaena and Microcystis were detected in this area.

Assessing the diversity of the g23 gene of T4-like bacteriophages from Lake Baikal with high-throughput sequencing

Abstract Based on second generation sequencing (MiSeq platform, Illumina), we determined the genetic diversity of T4‐like bacteriophages of the family Myoviridae by analysing fragments of the major capsid protein gene g23 in the plankton of Lake Baikal. The sampling depth in our study was significantly higher than in those obtained by the Sanger method before. We obtained 33 701 sequences of the g23 gene fragments, 141 operational taxonomic units (OTUs) of which were identified. 86 OTUs (60.9%) had the closest relatives from lakes Bourget and Annecy, and 28 OTUs (19.8%) had the highest identity with the Baikal g23 clones, which had been previously identified in the northern and southern basins of the lake by the Sanger method. The remaining OTUs were similar to the clones from other ecosystems. We showed a high genetic diversity of T4‐type bacteriophages and a genetic difference with the phage communities from other ecosystems. Figure. No Caption available.