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Long-chain alkenones (LCAs)—lipides produced by some microalgae of the Haptophyta group in seas and continental water bodies—are promising paleomarkers of climate changes because they are well-preserved in bottom sediments. The hydrocarbon chain and the degree of unsaturation of double bonds of this class of lipides can vary depending on habitat conditions of their producers. For the first time, we have discovered LCAs in the bottom sediments of two saline meromictic lakes Shira and Uchum located in arid steppes of southern Siberia (the North Minusinsk Depression) and estimated the distribution of their total content, length, and the degree of unsaturation. The highly abundant population of producers of LCAs—haptophyte algae of the genus Isochrysis (Haptophyta)—is revealed in the water column of Lake Uchum. It is shown that the species composition of the haptophyte algae and composition of the LCAs in the lakes under study are similar to those in saline stratified lakes of North America (Saskatchewan, Canada) with a similar climate and salt composition. The abundance of the С37:4 alkenone in the bottom sediments in the last 100 years reflected the variations in lake salinity caused by the documented changes in the water level. In this way, it is shown that the LCAs may be used as a paleomarker of climate-driven changes in the water level of the saline lakes in southern Siberia.

Lake Uchum is a newly defined meromictic lake in Siberia with clear seasonal changes in its mixolimnion. This study characterized the temporal dynamics and vertical profile of bacterial communities in oxic and anoxic zones of the lake across all four seasons: October (autumn), March (winter), May (spring), and August (summer). Bacterial richness and diversity in the anoxic zone varied widely between time points. Proteobacteria was the dominant bacterial phylum throughout the oxic and anoxic zones across all four seasons. Alphaproteobacteria (Loktanella) and Gammaproteobacteria (Aliidiomarina) exhibited the highest abundance in the oxic and anoxic zone, respectively. Furthermore, there was a successional shift in sulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria in the anoxic zone across the seasons. The most dominant SRB, Desulfonatronovibrio sp., is likely one of the main producers of hydrogen sulfide (H2S) and typically accumulates the most H2S in winter. The representative anoxygenic phototrophic bacterial group in Lake Uchum was purple sulfur bacteria (PSB). PSB were dominant (60.76%) in summer, but only had 0.2-1.5% relative abundance from autumn to spring. Multivariate analysis revealed that the abundance of these SRB and PSB correlated to the concentration of H2S in Lake Uchum. Taken together, this study provides insights into the relationships between changes in bacterial community and environmental features in Lake Uchum.

Long-term measurements show that the sedimentation dynamics of okenone (a carotenoid of purple sulfur bacteria) reflects the abundance of purple sulfur bacteria, the hydrogen sulfide content, and the stratification stability in the closed saline meromictic Shira Lake (Southern Siberia, Russia). The profile of fossil okenone in bottom sediments has been compared with the data on the water surface level in the lake over the last 100 years. The peaks of okenone correspond to lake transgressions, and the drops in the okenone content coincide with periods of stable or decreasing water level. Our observations show that fossil okenone may be used as a qualitative proxy of meromictic conditions and as a quantitative proxy of the water level dynamics in closed stratified lakes. Therefore, okenone can be used for qualitative reconstructions of the water balance and climate humidity in arid zones.

Meromictic lakes usually harbour certain prevailing anoxygenic phototrophic bacteria in their anoxic zone, such as the purple sulfur bacterium (PSB) Thiocapsa sp. LSW (hereafter LSW) in Lake Shunet, Siberia. PSBs have been suggested to play a vital role in carbon, nitrogen and sulfur cycling at the oxic–anoxic interface of stratified lakes; however, the ecological significance of PSBs in the lake remains poorly understood. In this study, we explored the potential ecological role of LSW using a deep-sequencing analysis of single-cell genomics associated with flow cytometry. An approximately 2.7 Mb draft genome was obtained based on the co-assembly of five single-cell genomes. LSW might grow photolithoautotrophically and could play putative roles not only as a carbon fixer and diazotroph, but also as a sulfate reducer/oxidizer in the lake. This study provides insights into the potential ecological role of Thiocapsa sp. in meromictic lakes.

Dynamics of abscisic acid (ABA) and indole-3-acetic acid (IAA) contents were followed in developing barley caryopses of the ABA-deficient mutant AZ34 and its parental cultivar Steptoe. Distribution of these hormones and HvPIP2 aquaporins (AQPs) was studied with the help of immunohistochemical methods in the roots and coleorhiza of developing embryos. In Steptoe, maturation of the caryopsis was accompanied by vast accumulation of ABA, while this hormone accumulated more slowly in the caryopsis of AZ34 and its content was lower than in Steptoe. Accumulation of ABA was accompanied by a decline in IAA level in the developing caryopsis, the process being delayed in AZ34 in accordance with the slower accumulation of ABA. ABA accumulated to high levels in the coleorhiza cells of Steptoe, while the effect was absent in AZ34. The high level of ABA was likely to be important for maintaining the barrier function of the coleorhiza, preventing germination of seminal roots and enabling seed dormancy, while the absence of ABA accumulation in coleorhiza of AZ34 may be responsible for the initiation of root germination inside the caryopsis. The abundance of HvPIP2 AQPs in the seminal roots was higher at the beginning of maturation of Steptoe caryopsis and declined afterwards, while the levels of APQs increased later in AZ34 in accordance with the delay in ABA accumulation. These results suggest the importance of ABA accumulation in coleorhiza for preventing precocious growth of seminal roots, and suggest regulation of IAA and aquaporin levels by this hormone during maturation of embryos.

Most of Earth’s bacteria have yet to be cultivated. The metabolic and functional potentials of these uncultivated microorganisms thus remain mysterious, and the metagenome-assembled genome (MAG) approach is the most robust method for uncovering these potentials. However, MAGs discovered by conventional metagenomic assembly and binning are usually highly fragmented genomes with heterogeneous sequence contamination. In this study, we combined Illumina and Nanopore data to develop a new workflow to reconstruct 233 MAGs—six novel bacterial orders, 20 families, 66 genera, and 154 species—from Lake Shunet, a secluded meromictic lake in Siberia. With our workflow, the average N50 of reconstructed MAGs greatly increased 10–40-fold compared to when the conventional Illumina assembly and binning method were used. More importantly, six complete MAGs were recovered from our datasets. The recovery of 154 novel species MAGs from a rarely explored lake greatly expands the current bacterial genome encyclopedia., Chen and colleagues develop a workflow for assembling high quality metagenome-associated genomes for microbial species using long and short reads, in this case from a meromictic lake. A full, detailed workflow is provided in for use by the community.

A psychrotolerant, methylotrophic methanogen, strain YSF-03T, was isolated from the saline meromictic Lake Shira in Siberia. Cells of strain YSF-03T were non-motile, irregular cocci and 0.8–1.2 µm in diameter. The methanogenic substrates utilized by strain YSF-03T were methanol and trimethylamine. The temperature range of growth for strain YSF-03T was from 0 to 37 °C. The optimum growth conditions were 30–37 °C, pH 7.0–7.4 and 0.17 M NaCl. The G+C content of the genome of strain YSF-03T was 41.3 mol%. Phylogenetic analysis revealed that strain YSF-03T was most closely related to Methanolobus profundi MobMT (98.15 % similarity in 16S rRNA gene sequence). Genome relatedness between strain YSF-03T and MobMT was computed using the Genome-to-Genome Distance Calculator and average nucleotide identity, which gave values of 23.5 and 79.3 %, respectively. Based on the morphological, phenotypic, phylogenetic and genomic relatedness data presented here, it is evident that strain YSF-03T represents a novel species of the genus Methanolobus , for which the name Methanolobus psychrotolerans sp. nov. is proposed. The type strain is YSF-03T (=BCRC AR10049T=DSM 104044T=NBRC 112514T).

In meromictic saline Lake Shira (southern Siberia, Russia) we revealed the dependence of okenone (specific carotenoid of purple sulfur bacteria) on water level dynamics. Therefore, we have shown that okenone in bottom sediments can be used as a proxy of climate humidity in semi-arid region of Southern Siberia.

A diverse series of 43 novel “soft antimicrobials” based on quaternary ammonium pyridoxine derivatives which include six-membered acetals and ketals of pyridoxine bound via cleavable linker moieties (amide, ester) with a fragment of fatty carboxylic acid was designed. Nine compounds exhibited in vitro promising antibacterial activity against Gram-positive and Gram-negative bacterial strains with MIC values comparable with reference antiseptics miramistin, benzalkonium chloride and chlorohexidine. On various clinical isolates, the lead compounds 6i and 12a exhibited antibacterial activity comparable with that of benzalkonium chloride while higher than that of miramistin. Moreover, 6i and 12a were able to kill bacteria embedded into the matrix of mono- and dual species biofilms. The treatment of bacterial cells by either 6i and 12a lead to fast depolarization of the membrane suggesting that the membrane is an apparent molecular target of compounds. 6i and 12a were non mutagenic neither in SOS-chromotest nor in Ames test and non-toxic in vivo at acute oral (LD50 > 2000 mg/kg) and cutaneous administration (LD50 > 2500 mg/kg) on mice. Taken together, our data allow suggesting described active compounds as promising starting point for the new antibacterial agents development.

Plant organogenesis remains one of the most essential questions of plant developmental biology. Callus tissue in vitro is a valuable tool for the studies on hormonal aspects of plant organogenesis, especially its early events, and immunohistochemical analysis is one of the few approaches offering information on the localization and role of hormones during organ development. The localization of endogenous zeatin and indole-3-acetic acid was investigated during simultaneous bud and root formation in calluses derived from immature embryos of wheat (Triticum aestivum L.). Calluses were induced on Murashige and Skoog (MS) medium supplemented with 2.0 mg L−1 2,4-dichlorophenoxyacetic acid. To stimulate simultaneous bud and root formation, calluses were transferred onto MS medium supplemented with 0.2 mg L−1 kinetin and 0.2 mg L−1 indoleacetic acid. Strong immunostaining for both hormones was detected in proliferating callus tissue, in developing meristematic centers and meristematic zones (whose cells were shown to be involved in organ formation), and at the sites of shoot and root apex initiation. During further development, shoot apexes with leaf primordia were heavily immunostained for zeatin, while immunostaining for indole-3-acetic acid was more intense at the sites of leaf primordia initiation and incipient primordia themselves. In the developing roots, immunostaining for both hormones reached a maximum in the root apex and gradually declined with increasing distance from the apex. Cells of developing procambial strands were also strongly stained for both zeatin and indole-3-acetic acid. These data suggest considerable similarity between patterns of hormone distribution in organs in vitro and in vivo. Thus, callus culture is a convenient and useful model for the study of fundamental biological questions such as how hormones regulate development.

A series of 108 novel quaternary bis-ammonium pyridoxine derivatives carrying various substituents at the quaternary nitrogen&rsquo, s and acetal carbon was synthesized. Thirteen compounds exhibited antibacterial and antifungal activity (minimum inhibitory concentration (MIC) 0.25&ndash, 16 &micro, g/mL) comparable or superior than miramistin, benzalkonium chloride, and chlorhexidine. A strong correlation between the lipophilicity and antibacterial activity was found. The most active compounds had logP values in the range of 1&ndash, 3, while compounds with logP &gt, 6 and logP &lt, 0 were almost inactive. All active compounds demonstrated cytotoxicity comparable with miramistin and chlorhexidine on HEK-293 cells and were three-fold less toxic when compared to benzalkonium chloride. The antibacterial activity of leading compound 5c12 on biofilm-embedded Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli or Pseudomonas aeruginosa was comparable or even higher than that of the benzalkonium chloride. In vivo 5c12 was considerably less toxic (LD50 1705 mg/kg) than benzalkonium chloride, miramistine, and chlorhexidine at oral administration on CD-1 mice. An aqueous solution of 5c12 (0.2%) was shown to be comparable to reference drugs efficiency on the rat&rsquo, s skin model. The molecular target of 5c12 seems to be a cellular membrane as other quaternary ammonium salts. The obtained results make the described quaternary bis-ammonium pyridoxine derivatives promising and lead molecules in the development of the new antiseptics with a broad spectrum of antimicrobial activity.

Eight species of charophytes have been found in the vast area of the ubiquitous permafrost in Far North-East Asia (i.e. the Republic of Sakha (Yakutia), the Magadan Region, and the Chukotka Autonomous Area, Russia): Chara contraria, C. globularis, C. strigosa, C. virgata, Nitella flexilis, N. opaca, N. wahlbergiana and Tolypella canadensis. Charophytes are found in a variety of water bodies and watercourses in areas with various thicknesses of permafrost, within the boreal and subarctic climate zones. Charophyte habitats are mostly associated with the distribution of carbonate rocks. The number of species and their records decrease towards north and east mainly due to shortening of the vegetation period. The highest density of records of charophytes and their most northern records are in river valleys, where the topography and heating effect of the river mitigate the influence of climate and permafrost. This association can be used to model and predict charophyte distribution in periglacial areas during glaciation. Widespread eurytopic species with a flexible life cycle, Chara contraria and C. globularis, are found in valley water bodies due to their ability to withstand environmental variation associated with marked changes in water temperature and flood disturbance. Rare perennial species such as C. strigosa and Tolypella canadensis are represented in deep lakes with less variation in environmental conditions. This paper discusses the distribution, habitat and life history strategies of charophytes that exist in the severe conditions of the permafrost area in Far North-East Asia based on previously published and new data.

Lakes Shira and Shunet (South Siberia, Russia) are saline ectogenic meromictic lakes. This meromixis is annually sustained by ice formation in winter. In spring due to melting of ice the second halocline is formed in the near-surface layers of mixolimnion that prevents the lakes from full circulation. During our observations (1998–2014) the mixolimnion in both the lakes was monomictic and undergone full circulation in autumn. Purple and green sulphur bacteria are abundant in the chemocline ; the phytoplankton diversity is relatively low; the major constituents of the zooplankton community are several genera of ciliates, calanoid copepod Arctodiaptomus salinus, rotifers Brachionus plicatilis and Hexarthra sp.; Paleolimnological study of the content of organic matter in sediments and the concentration of okenone demonstrated that Lake Shira was holomictic about 90 years ago when the water level was low. It became strongly meromictic just after the water level increase in the 1940s.

Cytokinin flow from roots to shoots can serve as a long-distance signal important for root-to-shoot communication. In the past, changes in cytokinin flow from roots to shoots have been mainly attributed to changes in the rate of synthesis or breakdown in the roots. The present research tested the possibility that active uptake of cytokinin by root cells may also influence its export to shoots. To this end, we collapsed the proton gradient across root membranes using the protonophore carbonyl cyanide m-chlorophenylhydrazone (CCCP) to inhibit secondary active uptake of exogenous and endogenous cytokinins. We report the impact of CCCP on cytokinin concentrations and delivery in xylem sap and on accumulation in shoots of 7-day-old wheat plants in the presence and absence of exogenous cytokinin applied as zeatin. Zeatin treatment increased the total accumulation of cytokinin in roots and shoots but the effect was smaller for the shoots. Immunohistochemical localization of cytokinins using zeatin-specific antibodies showed an increase in immunostaining of the cells adjacent to xylem in the roots of zeatin-treated plants. Inhibition of secondary active cytokinin uptake by CCCP application decreased cytokinin accumulation in root cells but increased both flow from the roots and accumulation in the shoots. The possible importance of secondary active uptake of cytokinins by root cells for the control of their export to the shoot is discussed.

For the first time the presence of gibel carp Carassius gibelio has been detected in the brackish meromictic Lake Shira (Southern Siberia, Republic of Khakassia). Lake Shira has been continuously studied since the late 19th century, and it has been considered so far that there is no ichthyofauna in the lake. This work investigates the growth and population characteristics, as well as food spectra and fatty acid composition of C. gibelio specimen at different ages that were fished out in the summers of 2007 and 2008. The water salinity at the fishing point was 15 g l-1. The food spectrum of oneand two-year old C. gibelio was dominated by diatomic, green and blue-green algae, while fourto sixyear old species had an increased share of copepods, beetles and chironomids in their food spectrum, and beginning from the age of six years the amphipods Gammarus lacustris consisted significant part of gibel carp diet. Thus, it was shown that C. gibelio is a carnivore with regard to the population of amphipods Gammarus lacustris, which have been regarded so far as the upper link in the trophic cascade of Lake Shira. One of the possible reasons for appearance of fish is the decreased water salinity caused by rising of the lake level. In the recent years, the level of Lake Shira exceeded all the values that had been registered since the late 19th century, and the lake’s salinity decreased correspondingly to its smallest value for the whole period of observation.

The vertical and seasonal distributions of the phytoflagellate Cryptomonas spp., and its most common, the planktonic ciliate predators (Oligotrichida, Scuticociliatida, Hypotrichida and Prostomatida) were investigated in chemocline region of small saline, meromictic lake Shunet (Siberia, Russia) during 2003 and 2005. The lake has a pronounced chemocline, with abundance of purple and green sulphur bacteria. Vertical distribution of the Cryptomonas populations near the oxic/anoxic boundary layer was studied at close intervals in water sampled using a hydraulically operated thin-layer sampler. In both summer and winter, Cryptomonas peaked in water stratum 5–10 cm above anoxic zone or in the anoxic zone water column in the chemocline (about 5 m). Ciliate densities and biomass were also much higher in chemocline than in mixolimnion. The range of diurnal migration of Cryptomonas population was not very wide, and it was restricted to layers with high light intensity. The ciliates were sometimes detected above the upper border of the anoxic zone but also several centimetres below this zone.

Meromictic lakes located in landlocked steppes of central Asia (~2500 km inland) have unique geophysiochemical characteristics compared to other meromictic lakes. To characterize their bacteria and elucidate relationships between those bacteria and surrounding environments, water samples were collected from three saline meromictic lakes (Lakes Shira, Shunet and Oigon) in the border between Siberia and the West Mongolia, near the center of Asia. Based on in-depth tag pyrosequencing, bacterial communities were highly variable and dissimilar among lakes and between oxic and anoxic layers within individual lakes. Proteobacteria, Bacteroidetes, Cyanobacteria, Actinobacteria and Firmicutes were the most abundant phyla, whereas three genera of purple sulfur bacteria (a novel genus, Thiocapsa and Halochromatium) were predominant bacterial components in the anoxic layer of Lake Shira (~20.6% of relative abundance), Lake Shunet (~27.1%) and Lake Oigon (~9.25%), respectively. However, few known green sulfur bacteria were detected. Notably, 3.94% of all sequencing reads were classified into 19 candidate divisions, which was especially high (23.12%) in the anoxic layer of Lake Shunet. Furthermore, several hydro-parameters (temperature, pH, dissolved oxygen, H2S and salinity) were associated (P< 0.05) with variations in dominant bacterial groups. In conclusion, based on highly variable bacterial composition in water layers or lakes, we inferred that the meromictic ecosystem was characterized by high diversity and heterogenous niches.

Strain AIST, an aerobic halophilic, Gram-reaction-negative, heterotrophic bacterium isolated from the water of Shira Lake in Khakasia, southern Siberia, was characterized using a polyphasic approach. Our analysis of the 16S rRNA gene sequences showed that ‘Aliidiomarina haloalkalitolerans’, ‘Aliidiomarina sanyensis’, Idiomarina maris and AIST formed a distinct lineage. The sequence similarities between AIST and the type strains of species of the genera Idiomarina and Aliidiomarina were 91.6–95.1 % and 94.0–96.9 %, respectively. The major isoprenoid quinone of AIST was ubiquinone 8 (Q-8). Predominant cellular fatty acids were iso-C17 : 0, iso-C15 : 0 and summed feature 9. The genomic DNA G+C content was 45.8 mol%. It is concluded that AIST represents a novel species of the genus Aliidiomarina , and the name Aliidiomarina shirensis sp. nov. is herein proposed for it. The type strain is AIST ( = JCM 17761T = BCRC 80327T). Based on its fatty acid profile and our phylogenetic analysis, we propose that Idiomarina maris be transferred to the genus Aliidiomarina .

Direct determination of RNA-protein complex structures is often facilitated by the use of thermophilic proteins; however E. coli is the most investigated system so far. A hybrid approach is to form heterologous complexes of E. coli RNA with thermophilic proteins. The rationale for this approach to RNA-protein interactions in ribosomes is based on the ability of the thermophilic protein S7 to replace a homologous counterpart in vivo. In vitro, the protein S7 of Thermus thermophilus is able to form complexes with both the minimal 16S rRNA fragment and the intercistronic region of the str operon mRNA from E. coli (Kd = 1.4 x 10(7) M and 1.1 x 10(-7) M respectively). The interaction of Thermus S7 with the E. coli intercistronic mRNA is surprising, because this region does not exist in the thermophilic str operon. It suggests a high degree of conservation of an RNA-binding site on S7.

The human nuclear single-stranded (ss) DNA- binding protein, replication protein A (RPA), is a heterotrimer consisting of three subunits: p70, p32 and p14. The protein–DNA interaction is mediated by several DNA-binding domains (DBDs): two major (A and B, also known as p70A and p70B) and several minor (C and D, also known as p70C and p32D, and, presumably, by p70N). Here, using crosslinking experiments, we investigated an interaction of RPA deletion mutants containing a subset of the DBDs with partial DNA duplexes containing 5′-protruding ssDNA tails of 10, 20 and 30 nt. The crosslinks were generated using either a ‘zero-length’ photoreactive group (4-thio-2′-deoxyuridine-5′-monophosphate) embedded in the 3′ end of the DNA primer, or a group connected to the 3′ end by a lengthy linker (5-{N-[N-(4-azido-2,5-difluoro-3- chloropyridine-6-yl)-3-aminopropionyl]-trans-3-aminopropenyl-1}-2′-deoxyuridine-5′-monophosphate). In the absence of two major DBDs, p70A and p70B, the RPA trimerization core (p70C·p32D·p14) was capable of correctly recognizing the primer– template junction and adopting an orientation similar to that in native RPA. Both p70C and p32D contributed to this recognition. However, the domain contribution differed depending on the size of the ssDNA. In contrast with the trimerization core, the RPA dimerization core (p32D·p14) was incapable of detectably recognizing the DNA- junction structures, suggesting an orchestrating role for p70C in this process.

Replication protein A (RPA), the nuclear single-stranded DNA binding protein is involved in DNA replication, nucleotide excision repair (NER) and homologous recombination. It is a stable heterotrimer consisting of subunits with molecular masses of 70, 32 and 14 kDa (p70, p32 and p14, respectively). Gapped DNA structures are common intermediates during DNA replication and NER. To analyze the interaction of RPA and its subunits with gapped DNA we designed structures containing 9 and 30 nucleotide gaps with a photoreactive arylazido group at the 3′-end of the upstream oligonucleotide or at the 5′-end of the downstream oligonucleotide. UV crosslinking and subsequent analysis showed that the p70 subunit mainly interacts with the 5′-end of DNA irrespective of DNA structure, while the subunit orientation towards the 3′-end of DNA in the gap structures strongly depends on the gap size. The results are compared with the data obtained previously with the primer–template systems containing 5′- or 3′-protruding DNA strands. Our results suggest a model of polar RPA binding to the gapped DNA.

This article presents evidence that protein kinase activity is an intrinsic property of secretory immunoglobulin A (sIgA) from milk of healthy human mothers. Polyclonal sIgA was purified by sequential chromatography on protein A-Sepharose, DEAE-cellulose, and gel filtration on Toyopearl HW-55 and Sepharose 4B columns. Its purity was established by one- and two-dimensional SDS-PAGE. The protein kinase activity was inhibited by specific antibodies (Abs) against sIgA, and was stable to acidic and alkaline conditions. Catalytic sIgA showed optimal reaction conditions (pH and MgCl2 concentration) and substrate specificity different from those of known protein kinases; i.e., sIgA phosphorylated the serine residues of various milk proteins in the presence of different gamma-[32P]nucleoside- and deoxynucleoside-5'-triphosphates. The homogeneous Fab fragment of sIgA also showed kinase activity. An ATP-binding activity of fractions of sIgA was demonstrated by affinity chromatography on ATP-Sepharose and by covalent binding of an affinity analog of ATP; this activity was mediated by the L chain of sIgA. The authors believe these observations are the first example of the catalytic activity of IgA Abs and of natural catalytic Abs with synthetic activity. In addition, the findings suggest the likelihood that catalytic Abs are generated by the immune system of healthy mothers.

Various catalytically active antibodies (Abs), or abzymes, have been detected recently in the sera of patients with autoimmune pathologies, in whom their presence is probably associated with autoimmunization. Normal humans are generally not considered to have abzymes, since no obvious immunizing factors are present. Here is shown by different methods that IgG from the milk of normal females possesses both DNase and RNase activities. The activities were also present in the IgG F(ab′)2 and Fab fragments. Affinity modification of IgG by the chemically reactive derivative of an oligonucleotide led to preferential modification of the L chain of IgG. After separation of the subunits by sodium dodecyl sulfate electrophoresis in a gel containing DNA, an in-gel assay showed DNase activity in the L chain. The L chain separated by affinity chromatography on DNA-cellulose was catalytically active. These findings speak in favor of the generation of cat alytic Abs by the immune system of healthy mothers. It is known that the treatment of adults with DNases and RNases offers protection from viral and bacterial diseases. Since breast milk protects the infants from infec tions until the immune system is developed, this raises the possibility that catalytic Abs like nucleases, may possess a protective role.

A feature of meromictic lakes is that several physicochemical and biological gradients affect the vertical distribution of different organisms. The vertical stratification of physical, chemical and biological components in saline, fishless meromictic lakes Shira and Shunet (Siberia, Russia) is quite different mainly because both mean depth and maximum depth of lakes differ as well as their salinity levels differ. The chemocline of the Lake Shira, as in many meromictic lakes, is inhabited by bacterial community consisting of purple sulphur and heterotrophic bacteria. As the depth of the chemocline is variable, the bacterial community does not attain high densities. The mixolimnion in Lake Shira, which is thermally stratified in summer, also creates different habitat for various species. The distribution of phytoplankton is non-uniform with its biomass peak in the metalimnion. The distribution of zooplankton is also heterogeneous with rotifers and juvenile copepods inhabiting the warmer epilimnion and older copepods found in the cold but oxic hypolimnion. The amphipod Gammarus lacustris which can be assigned to the higher trophic link in the fishless lake’s ecosystem, such as Lake Shira, is also distributed non-uniformly, with its peak density generally observed in the thermocline region. The chemocline in Lake Shunet is located at the depth of 5 m, and unlike in Lake Shira, due to a sharp salinity gradient between the mixolimnion and monimolimnion, this depth is very stable. The mixolimnion in Lake Shunet is relatively shallow and the chemocline is inhabited by (1) an extremely dense bacterial community; (2) a population of Cryptomonas sp.; and (3) ciliate community comprising several species. As the mixolimnion of Lake Shunet is not thermally stratified for long period, the phytoplankton and zooplankton populations are not vertically stratified. The gammarids, however, tend to concentrate in a narrow layer located 1–2 m above the chemocline. We believe that in addition to vertical inhomogeneities of both physicochemical parameters, biological and physical factors also play a role in maintaining these inhomogeneities. We conclude that the stratified distributions of the major food web components will have several implications for ecosystem structure and dynamics. Trophic interactions as well as mass and energy flows can be significantly impacted by such heterogeneous distributions. Species spatially separated even by relatively short distances, say a few centimetres will not directly compete. Importantly, we demonstrate that not only bacteria, phytoflagellates and ciliate tend to concentrate in thin layers but also larger-sized species such Gammarus (amphipods) can also under certain environmental conditions have stratified distribution with maxima in relatively thin layer. As the vertical structure of the lake ecosystem is rather complex in such stratified lakes as ours, the strategy of research, including sampling techniques, should consider potentially variable and non-homogeneous distributions.