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The paper is dedicated to the fundamental research problem of biochemical ecology, i.e. to the identification of interaction mechanisms of anthropogenic pollution and organisms. The data on Baikal lake hydrobionts filtration capacities are essential in order to determine their ecological value when using them in aquaculture. The paper presents the data on studies of Baikal lake endemic species Lubomirskia baicalensis in model experiments with polycyclic aromatic hydrocarbons which inhibit biodegradation, are carcinogenic, slow-soluble and tend to accumulate on the bottom of lake Baikal. The article discusses the results of the model experiments on the influence of priority toxicants (naphthalene, anthracene, pyrene) on the endemic species Lubomirskia baicalensis, carried out in 2015–2016. A comparative analysis with the data of the 2006 experiment is given. The change of the content of polycyclic aromatic hydrocarbons in healthy and sick sponges is shown. The authors draw a conclusion that the highest rate of decrease in content is observed during the first hours of 6–12 hour exposure and within 24–36 hours of exposure, approximately 5–10 % of the stock concentration of polycyclic aromatic hydrocarbons remains in the water.

Endemic freshwater sponges (demosponges, Lubomirskiidae) dominate in Lake Baikal, Central Siberia, Russia. These sponges are multicellular filter-feeding animals that represent a complex consortium of many species of eukaryotes and prokaryotes. In recent years, mass disease and death of Lubomirskia baicalensis has been a significant problem in Lake Baikal. The etiology and ecology of these events remain unknown. Bacteria from the families Flavobacteriaceae and Oxalobacteraceae dominate the microbiomes of diseased sponges. Both species are opportunistic pathogens common in freshwater ecosystems. The aim of our study was to analyze the genomes of strains Janthinobacterium sp. SLB01 and Flavobacterium sp. SLB02, isolated from diseased sponges to identify the reasons for their joint dominance. Janthinobacterium sp. SLB01 attacks other cells using a type VI secretion system and suppresses gram-positive bacteria with violacein, and regulates its own activity via quorum sensing. It produces floc and strong biofilm by exopolysaccharide biosynthesis and PEP-CTERM/XrtA protein expression. Flavobacterium sp. SLB02 utilizes the fragments of cell walls produced by polysaccharides. These two strains have a marked difference in carbohydrate acquisition. We described a possible means of joint occupation of the ecological niche in the freshwater sponge microbial community. This study expands the understanding of the symbiotic relationship of microorganisms with freshwater Baikal sponges.

Endemic freshwater sponges (demosponges, Lubomirskiidae) dominate in Lake Baikal, Central Siberia, Russia. These sponges are multicellular filter-feeding animals that represent a complex consortium of many species of eukaryotes and prokaryotes. In recent years, mass disease and death of Lubomirskia baicalensis has been a significant problem in Lake Baikal. The etiology and ecology of these events remain unknown. Bacteria from the families Flavobacteriaceae and Oxalobacteraceae dominate the microbiomes of diseased sponges. Both species are opportunistic pathogens common in freshwater ecosystems. The aim of our study was to analyze the genomes of strains Janthinobacterium sp. SLB01 and Flavobacterium sp. SLB02, isolated from diseased sponges to identify the reasons for their joint dominance. Janthinobacterium sp. SLB01 attacks other cells using a type VI secretion system and suppresses gram-positive bacteria with violacein, and regulates its own activity via quorum sensing. It produces floc and strong biofilm by exopolysaccharide biosynthesis and PEP-CTERM/XrtA protein expression. Flavobacterium sp. SLB02 utilizes the fragments of cell walls produced by polysaccharides. These two strains have a marked difference in carbohydrate acquisition. We described a possible means of joint occupation of the ecological niche in the freshwater sponge microbial community. This study expands the understanding of the symbiotic relationship of microorganisms with freshwater Baikal sponges.

There are significant changes in the consortium of microorganisms of freshwater Baikal sponges during their mass death, which began in 2011. The alleged cause of disease is a significant increase in the number of opportunistic microorganisms. Here, we report the draft genome sequence of Flavobacterium sp. strain SLB02.

A mass bleaching event affecting an endemic Baikal sponge points out the need to study stress responses in these organisms. To get the first data about Hsp70 content changes in endemic Baikal sponge Lubomirskia baicalensis during exposure to elevated temperatures which can occur in its natural habitat, we investigated the effect of two elevated temperatures on Hsp70 levels in the L. baicalensis and its cell aggregates (primmorphs). After increasing the water temperature from ambient 4 to 9 °C Hsp70 levels increased to protect against temperature stress. Incubation at 13 °C for one month resulted in bleaching and death of the sponges. The decreased level of HSP70 was recorded both in the case of bleaching after exposure to 13 °C, and in diseased individuals from the Lake Baikal. The L. baicalensis primmorph temperature stress response was not consistent with that of the sponge. In primmorphs, the Hsp70 level initially decreased at 4 °C and at 13 °C it increased compared with the levels observed in the sponge. Thus, our results show that primmorphs are not a good model system for the study of expression of stress proteins in sponges. Since the temperatures 9–13 °C were observed at L. baicalensis habitats, climate warming may increase vulnerability of this sponge to bleaching.

In recent years, the surfaces of endemic Baikalian sponges have exhibited signs of damage and disease such as tissue bleaching, atypical microbial films, and necrotic areas. One of the most common sources of damage on branching sponges Lubomirskia baicalensis is a reddish-brown mucous film fully or partially covering the body of the sponge. Sequencing of the 16S rDNA gene revealed that the film on the surfaces of the sponge consists of Oscillatoriales cyanobacteria belonging to the following genera: Tychonema, Phormidium, and Leptolyngbya, with 44 of the 86 identified sequences belonging to Tychonema. Cyanobacterial fouling of the Baikalian sponge may be caused by changes in environmental conditions of the sponge habitat, in particular, temperature increases and eutrophication of the lakes.

Two new nematode species of the genus Tobrilus Andrássy, 1959 from Lake Baikal are described and illustrated. The first species Tobrilus elginus sp. nov. was found in the littoral zone of Maloye More Bays. The second species Tobrilus juliae sp. nov. dwells on bodies of dead sponges Lubomirskia baicalensis (Pallas, 1776). Tobrilus elginus sp. nov. is most similar to T. amabilis Tsalolikhin, 1974 and T. bekmanae Tsalolikhin, 1975. In contrast to the first species it has a shorter body and spicules, longer gubernaculum and a shorter supplements row. Its body is shorter and thinner, tail and supplement row are shorter and the vulva is more posterior as compared to the second species. The body size of Tobrilus juliae sp. nov. is most similar to T. securus Gagarin & Naumova, 2011 and T. saprophagus Naumova & Gagarin, 2017. From the first of these species it differs by the thinner body, shorter tail, comparatively shorter outer labial setae and shorter spicules. It differs from the second species by a thinner body, shorter male tail and shorter labial setae.

The fatty acid composition of visually health and sick Lubomirskia baicalensis sponges from Lake Baikal (years of 2016 and 2018) was determined. Sponges collected in 2018 had an abnormality of demospongic acid synthesis. Demospongic acids are of antibiotic activity and protect sponges. In vitro, there was an increase in the concentrations of the palmitic, oleic, linoleic and -linolenic sponge acid under stress. These substances are responsible for cell membrane repairing and antibiotically active. During three weeks, there were also demospongic acid synthesis termination and appearance of disease precursors was noted.

Проведен анализ влияния индукции силикатом натрия модельной клеточной культуры примморф байкальской губки Lubomirskia baicalensis на экспрессию силикатеинов и морфогенез спикул. Клеточную культуру примморф истощали по содержанию кремния путем культивирования на искусственной байкальской воде в течение месяца. Экспрессию генов белков, регулирующих метаболизм кремния, индуцировали добавлением силиката натрия до конечной концентрации 70 мкМ. Уровень экспрессии генов силикатеинов анализировали методом ПЦР в реальном режиме времени в первый, второй, третий и шестой дни после индукции. В качестве референсных генов для нормализации данных использовали β-актин (ACTB) и фактор элонгации 1 α (eEF1a1). Контрольными образцами служили пробы взрослой губки и образцы примморф, культивированных на натуральной и искусственной байкальской воде до индукции. Динамику образования и рост кремниевых спикул анализировали методами микроскопии. Образцы примморф, индуцированных добавлением силиката натрия, на фоне массового развития спикул не продемонстрировали значительного увеличения уровня экспрессии генов силикатеинов по сравнению с другими образцами (расхождение 1,7–2 относительных единиц). Такие значения не могут считаться статистически значимыми изменениями в степени экспрессии и лежат в пределах погрешности, что говорит о практически полном отсутствии индукции синтеза мРНК силикатеинов силикатом натрия. Этот факт свидетельствует о пассивности силикатеинов на начальных этапах метаболизма кремния и необходимости поиска других соединений, влияющих на отложение биогенного кремнезема в спикулах губок.

The skeletal elements (spicules) of the demosponge Lubomirskia baicalensis were analyzed; they are composed of amorphous, non-crystalline silica, and contain in a central axial canal the axial filament which consists of the enzyme silicatein. The axial filament, that orients the spicule in its longitudinal axis exists also in the center of the spines which decorate the spicule. During growth of the sponge, new serially arranged modules which are formed from longitudinally arranged spicule bundles are added at the tip of the branches. X-ray analysis revealed that these serial modules are separated from each other by septate zones (annuli). We describe that the longitudinal bundles of spicules of a new module originate from the apex of the earlier module from where they protrude. A cross section through the oscular/apical-basal axis shows that the bundle rays are organized in a concentric and radiate pattern. High resolution magnetic resonance microimaging studies showed that the silica spheres of the spicules in the cone region contain high amounts of 'mobile' water. We conclude that the radiate accretive growth pattern of sponges is initiated in the apical region (cones) by newly growing spicules which are characterized by high amounts of 'mobile' water; subsequently spicule bundles are formed laterally around the cones.

Sponges (Porifera) are among the simplest living and the earliest branching metazoans. They hold a pivotal role for studying genome evolution of the entire metazoan branch, both as an outgroup to Eumetazoa and as the closest branching phylum to the common ancestor of all multicellular animals (Urmetazoa). In order to assess the transcription inventory of sponges, we sequenced expressed sequence tag libraries of two demosponge species, Suberites domuncula and Lubomirskia baicalensis, and systematically analyzed the assembled sponge transcripts against their homologs from complete proteomes of six well-characterized metazoans--Nematostella vectensis, Caenorhabditis elegans, Drosophila melanogaster, Strongylocentrotus purpuratus, Ciona intestinalis, and Homo sapiens. We show that even the earliest metazoan species already have strikingly complex genomes in terms of gene content and functional repertoire and that the rich gene repertoire existed even before the emergence of true tissues, therefore further emphasizing the importance of gene loss and spatio-temporal changes in regulation of gene expression in shaping the metazoan genomes. Our findings further indicate that sponge and human genes generally show similarity levels higher than expected from their respective positions in metazoan phylogeny, providing direct evidence for slow rate of evolution in both "basal" and "apical" metazoan genome lineages. We propose that the ancestor of all metazoans had already had an unusually complex genome, thereby shifting the origins of genome complexity from Urbilateria to Urmetazoa.

(1884). III.—Some remarks upon the variability of form in Lubomirskia baicalensis, and upon the distribution of the Baikal sponges in general. Annals and Magazine of Natural History: Vol. 14, No. 79, pp. 29-34.