I. V. Khanaev

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.

Disturbances of the vertical zoning of green algae in the coastal part of the Listvennichnyi gulf of Lake Baikal

350 In recent decades, much attention is paid to evidi dence of anthropogenic pollution of the Lake Baikal ecosystem. However, to date, large scale changes in the flora in pelagic and coastal zones of the Lake Baikal have not been detected. Since the start of the Industrial Revolution in Siberia (the 1930s), no spe cies disappeared or emerged in the lake, with the exception of Elodea canadensis Michx., an aquarium plant, which got into the lake in 1978 [1]. In summer 2011, apparently for the first time, we were able to observe a large scale change in the flora of Lake Baikal as a result of a human impact on the open Listvennich nyi Gulf in the coastal zone in front of the Listvyanka village.

First detection of benthic cyanobacteria in Lake Baikal producing paralytic shellfish toxins

Cyanobacteria were screened from the surface of diseased sponges, stone and bedrock in Lake Baikal for the presence of saxitoxin using enzyme-linked immunosorbent assay. In sequel, eight paralytic shellfish toxin (PST) variants were identified using a MALDI mass spectrometry. Microscopic examination found that Tolypothrix distorta dominated in the biofouling samples. PCR and sequencing detected sxtA gene involved in saxitoxin biosynthesis, thereby providing evidence of the PST producing potential of Baikal cyanobacterial communities inhabiting different substrates.

Spirochetes in gastropods from Lake Baikal and North American freshwaters: new multi-family, multi-habitat host records

We describe the first records of spirochetes in the gut of fourteen species of continental gastropods from a range of habitats and representing six families (Amnicolidae, Baicaliidae, Bithyniidae, Pyrgulidae, Lithoglyphidae and Benedictiidae). The bacteria were mainly found in the crystalline style sac, as has been reported in marine bivalves. The surveyed habitats include water bodies in North America and Eurasia, including deep water hydrothermal vent and gas hydrate zones in Lake Baikal. Spirochetes were present both in mature and young snails, but were not detected in embryos before hatching, indicating lateral transfer. The surveyed gastropods range in trophic strategy, including phyto-, detrito- and bacteriophagous grazers and filter feeders. Our results indicate that spirochetes are commensal in the surveyed gastropods with potential limited benefit and no detriment to the host animal. We suggest that the specialized internal habitat of the crystalline style sac in molluscs is likely to reveal unrecognized spirochete diversity that will shed new light on gastropod trophic ecology and spirochete diversity.

The formation of a fouling community on artificial substrate in Lake Baikal

The development of a fouling community at the surface of an artificial substrate in the littoral zone of Lake Baikal was studied. This epibenthic community was composed of 23 diatom species and 57 invertebrate species. The core community consisted of molluscs and caddisflies feeding mostly on diatoms. In Lake Baikal a fouling community develops in a sequence similar to marine environments.

Biodiversity and food chains on the littoral bottoms of Lakes Baikal, Biwa, Malawi and Tanganyika: working hypotheses

Boreal Lake Baikal, temperate Lake Biwa, and tropical Lakes Malawi and Tanganyika each possess high biodiversities of benthic organisms in their littoral areas. Two general mechanisms influencing the evolutionary development of these high biodiversities can be hypothesized; i.e., a bottom-up constraint depending on the availability of food resources, and a top-down effect exerted by predators especially within the fish assemblage. The bottom-up constraint may be prominent where the abundance of benthic organisms in the grazing-food-chain is restricted by a seasonally lowest production, referring chiefly to attached algae, and large fluctuations in the abundance of primary producers provide a resource that is eventually utilized by benthic organisms of the detritus-food-chain. The top-down effect may be realized where the most of benthic organisms are supported by a constantly large primary production. These hypotheses help to explain, for the lakes we cite, the facts that diverse grazing-food-chain organisms live on the littoral bottom of tropical lakes where there is relatively constant large algal production due to suitable conditions of water temperature and light penetration through the year; while on the other hand, detritus-food-chain organisms are predominant on the littoral bottom of a boreal lake with seasonally fluctuating algal production and its pronounced lowest production in a year. In fish communities, segregations in habitat and food resource are important mechanisms allowing development of high species packing, while cohabitation within predatory fishes increases their feeding success due to the decrease of defensive efficiency by the threat of a variety of attacking methods. A further top-down effect may be exerted by scale-eating fishes, especially in Lake Tanganyika. The presence of such predatory and harmful members may promote more dense packing of prey members to increase their mutual defense efficiency.

The first case of disease of the sponge Lubomirskia baicalensis: Investigation of its microbiome

The first metagenomic analysis of the microbiome of the first sample of diseased endemic sponge Lubomirskia baicalensis (Pallas, 1771) from Lake Baikal and the comparison of the results with data published earlier on the microbiome of healthy sponges were carried out. Essential changes in the composition and structure of the microbial community were detected in the diseased individual possessing an uncharacteristic pink coloring. Cyanobacteria were predominant in the community, the fraction of the representatives of Verrucomicrobia was increased. The diversity and number of eukaryotic algae, as well as of representatives of Bacteroidetes, Proteobacteria, Actinobacteria, and Planctomycetes, were decreased. A wide range of minor phyla were eliminated. The factors affecting the composition of symbiotic communities in sponges were considered. It was supposed that changes in the structure of symbiotic communities resulting in mass disease and death could be caused by an increase in the methane concentration in the water column of Lake Baikal.

Isolation and identification of the microalgal symbiont from primmorphs of the endemic freshwater sponge Lubomirskia baicalensis (Lubomirskiidae, Porifera)

The first reports on the presence of zoochlorellae within the organelles of mesenchymal cells from freshwater sponges were published in the 19th century. Today, it is well-known that freshwater sponges can be found in association with different endosymbiotic algae. However, until now there has been no detailed information about the endosymbiotic chlorophyll-containing algae in the remarkable endemic green sponges from Lake Baikal. In our study we were able for the first time to isolate and identify endosymbionts from primmorphs cultivated in vitro, and to compare them with those from naturally occurring Lubomirskia baicalensis sponges. Structural as well as molecular biological investigations show that the endosymbiotic alga is a Mychonastes species closely related to M. huancayensis. Another novel aspect of our work was to show that it is possible to use primmorphs of endemic sponges for isolation and subsequent cultivation of their endosymbiotic algae. We employed a simple cold-water (3–4°C) approach for cultivating Mychonastes sp., both within sponge primmorphs and in culture.

Biogeochemical characteristics of dominant gastropod species from the stony littoral of southern Baikal

The trace element composition of dominant gastropod species from the littoral of southern Baikal was investigated. Both different mollusk species and their parts (shells and soft tissues) show specific trace element characteristics. The highest Sr and Ba contents were observed in Maackia herderiana. The highest Zn, Cu, and Cd and lowest Pb contents were detected in Megalovalvata baicalensis. Choanomphalus sp. shows high Mn and Ti and very low Sr, Cu, and Cd contents. Most of Cu, Zn, and Cd and a considerable fraction of Rb, Pb, Mo, Sc, Ce, W, Ga, Y, and Th are incorporated in the gastropod bodies. The maximum concentration of U is also characteristic of the body tissues. The foot tissues of Maackia herderiana and Megalovalvata baicalensis are depleted in the majority of elements compared with their bodies. Sr and Ba are prevalent in the mollusk shells, where high Mn contents were also detected. A close relationship was observed between the chemical compositions of the gastropods, stony substrate, and bottom water. Group concentration of trace elements is common in the species investigated. Relative to the bottom water layer, the gastropod species concentrate Ti, Mn, La, Co, Y, and V and show similarly low extraction of U, W, Mo, and Cs. Compared with the bottom sediments, the mollusks accumulate Sr. In addition, Maackia herderiana and Megalovalvata baicalensis accumulate Cd and Zn. Megalovalvata baicalensis is distinguished by the ability to concentrate Cu. The following sequence is formed by the gastropods with respect to their capacity to accumulate Cd, Zn, and Cu: Megalovalvata baicalensis > Maackia herderiana > Choanomphalus sp.

The effect of bloom of filamentous green algae on the reproduction of yellowfin sculpin Cottocomephorus grewingkii (Dybowski, 1874) (Cottoidae) during ecological crisis in Lake Baikal

In shallow water areas of open Lake Baikal, filamentous green alga of the genus Spirogyra grows abundantly. Together with alga of the genus Ulothrix, it forms algal mats. According to our observations from 2010 to 2013, the spawning habitat conditions for the yellowfin sculpin Cottocomephorus grewingkii (Dybowski, 1874) (Cottidae) proved to be significantly disturbed in the littoral zone of Listvennichnyi Bay (southern Baikal), which, in turn, reduced the number of egg layings. With a 100% projective cover of the floor and a high density of green filamentous algae, the shallow-water stony substrate becomes completely inaccessible for spawning of the August population.