Reproductive Strategies and the Origin of Parapatric and Sympatric Forms of Arctic Charr Salvelinus alpinus (Salmonidae) in the System of Lakes Bol’shoe Leprindo and Maloe Leprindo (Northern Transbaikalia)

Journal of Ichthyology - In the system of lakes Bol’shoe Leprindo and Maloe Leprindo (Lena basin, Transbaikalia), spawning of two isolated populations of the dwarf form of Arctic charr...     

The First Results of an Investigation into the Phylogenetic Diversity of Microorganisms in Southern Baikal Sediments in the Region of Subsurface Discharge of Methane Hydrates

Phylogenetic analysis of the bacterial communities in Lake Baikal bottom sediments in the region of subsurface methane hydrate discharge has been carried out using data on 16S rRNA sequences. The composition of these microbial communities is shown to be different in different horizons. Methanotrophic bacteria are found in the surface layer (0–5 cm), and uncultured bacteria constitute a great portion of this population. In deeper sediment layers (92–96 cm), a change in the microbial community occurs; specifically, a decreased homology with the known sequences is observed. The new sequences form separate clusters on a phylogenetic tree, indicating the possibly endemic nature of the bacteria revealed. Organisms related to the genus Pseudomonas constitute the main portion of the population. An archaea-related sequence was found in a horizon containing gas hydrate crystals (100–128 cm). Uncultured bacteria remain predominant.__________Translated from Mikrobiologiya, Vol. 74, No. 3, 2005, pp. 370–377.Original Russian Text Copyright © 2005 by Shubenkova, Zemskaya, Chernitsyna, Khlystov, Triboi.     

Ultrastructure of the sinus and atrioventricular nodes in experimental myocardial infarct

The ultrastructure of sinus and atrioventricular nodes was studied in white rats with experimental myocardial infarction. 24 hours after the induction of the disease mitochondrial enlargement characterized by the increase in their area, decrease in the number of cristae and the decline in the rate of mitochondrial energy effectiveness was detected. Different degrees of nuclear chromatin aggregation and membrane permeability for colloidal lanthanum were observed. Characteristic types of conduction cellular lesions were revealed in experimental myocardial infarction.     

Comparative characterization of microbial communities in two regions of natural oil seepage in Lake Baikal

Microbial communities and hydrocarbon contents have been studied in two regions of natural oil seepage in Lake Baikal: (1) opposite the Bol’shaya Zelenovskaya River mouth (studied previously) and (2) near Cape Gorevoi Utes (discovered in 2005). The abundance of both heterotrophic and hydrocarbon-oxidizing microorganisms is significantly higher in water samples from the first region, where the oil is biologically degraded. In the surface soil layer at stations located in the immediate vicinity of oil seepage site, the abundance of n-alkane-oxidizing microorganisms reaches 2000 cells/ml, and that of oil-oxidizing microorganisms reaches 2600 cells/ml. In water samples from near Cape Gorevoi Utes, the abundance of these groups of microorganisms does not exceed 190 and 500 cells/ml, respectively.     

Study on the Lake Baikal microbial community in the areas of the natural oil seeps

We studied the composition of a natural microbial community, the distribution of different groups of microorganisms (including those able to degrade oil hydrocarbons) within the areas of natural oil seeps in the Lake Baikal. It was revealed that, in the bottom sediments, the oil-degrading microorganisms dominating the community have included the bacteria of g. Bacillus, while in the water column, dominating microbes are presented by species of genera Rhodococcus Pseudomonas, and Micrococcus. Under the conditions of the model experiment, the potential activity of Baikal microbes towards utilization of n-alcanes has been assessed. Under such conditions it was shown that the concentration of n-alcanes decreases to 60% during 20 days of the experiment (the initial oil concentration was 0.5 mg/l, i.e., ten maximal permissible concentrations, MPC).     

Phylogenetic diversity of microbial communities of the Posolsk Bank bottom sediments,Lake Baikal

Massive parallel sequencing (the Roche 454 platform) of the 16S rRNA gene fragments was used to investigate microbial diversity in the sediments of the Posolsk Bank cold methane seep. Bacterial communities from all sediment horizons were found to contain members of the phyla Actinobacteria, Bacteroidetes, Deinococcus-Thermus, Firmicutes, Nitrospirae, Chloroflexi, Proteobacteria, and the candidate phyla Aminicenantes (OP8) and Atribacteria (OP9). Among Bacteria, members of the Chloroflexi and Proteobacteria were the most numerous (42 and 46%, respectively). Among archaea, the Thaumarchaeota predominated in the upper sediment layer (40.1%), while Bathyarchaeota (54.2%) and Euryarchaeota (95%) were predominant at 70 and 140 cm, respectively. Specific migration pathways of fluid flows circulating in the zone of gas hydrate stability (400 m) may be responsible for considerable numbers of the sequences of Chloroflexi, Acidobacteria, and the candidate phyla Aminicenantes and Atribacteria in the upper sediment layers and of the Deinococcus-Thermus phylum in deep bottom sediments.     

Comparative molecular biological analysis of the microbial community of the holocene and pleistocene deposits of Posol'skaya Shoal, Lake Baikal

The bacterial diversity was studied in sediment layers of Posol'skaya Shoal station (Southern Baikal) belonging to different periods. A set of primers specific to individual bacterial groups was used to analyze the 16S rRNA gene fragments. The bacterial diversity in the Holocene deposits was found to be higher than in the Pleistocene ones. In the upper sediments, a positive PCR reaction with bacterial primers and with specific cyanobacterial and archaebacterial primers was detected. The following phylogenetic groups were revealed in the microbial community of the surface horizon: green nonsulfur bacteria, delta-proteobacteria, beta-proteobacteria (Nitrospirae), alpha-proteobacteria, acidobacteria, crenarchaeota, euryarchaeota, and groups of uncultured bacteria. From the DNA of the Pleistocene deposits, the PCR product was obtained only with bacterial primers. The representatives of the genus Pseudomonas were most closely related to the sequences obtained (95-97% homology).     

Reproductive strategies of Arctic charr Salvelinus alpinus (L.) forms in Kiryalta lakes,Transbaikalia, Russia

Lake Abaya and Lake Chamo are the two largest Ethiopian Rift Valley lakes; they are located close to each other, but have a strikingly different water transparency. We explain key differences in the structure and the functioning of the food web with variation in limnological variables and major pelagic food web compartments within and across both lakes. Data from a detailed comparative investigation of physical and chemical variables and zooplankton community characteristics during the wet and dry season from two consecutive years revealed major differences in key limnological variables between Lake Abaya and Lake Chamo. The most pronounced differences were related to water transparency and the amount of suspended solids in the water column. Lake Abaya is much more turbid, has lower phyto- and zooplankton biomass, and has considerably lower primary production than Lake Chamo. Based on our results, we infer that the profound differences in food web structure between both lakes probably result from differences in sediment load. Finally, our results indicate that conservation programs should focus on reducing sediment inflow from the catchments into the lakes.

     

Trophic relationships between macroinvertebrates and fish in St. Petersburg methane seep community in abyssal zone of Lake Baikal

Trophic relationships were examined for macroinvertebrates and fish inhabiting the St. Petersburg methane seep (central part of Lake Baikal, ~1400 m depth). The analyses of the values of carbon and nitrogen stable isotopes showed that all animals associated with the seep were heterotrophs with different feeding strategies; symbiotrophes were absent. Seep animals consumed combined food with different portion of methanederived carbon ranged from 2.7 to 89%. The average δ¹³С values varied in the range of–26.2‰ (in benthopelagic amphipods) to–64.5‰ (in gastropods). The trophic food web in the methane seep consists of filter feeders (pelagic amphipods, trophic position (TP) is 1.9), detritophages (gastropods, TP of 2.2, and burrowing amphipods, TP of 2.1), polyphages and necrophages (nectobenthic and benthopelagic amphipods of TP 2.8–3.2), and predators (planarians of TP 3.6–4.2 and cottoid fish of TP 3.0–3.8). Animals occupying similar trophic positions significantly differed in the δ¹³С values and have partially overlapping components of food.     

Microbial diversity and authigenic siderite mediation in sediments surrounding the Kedr-1 mud volcano,Lake Baikal

The gas hydrate-bearing structure—mud volcano Kedr-1 (Lake Baikal, southern basin)—is located near the coal-bearing sediments of the Tankhoy formation of Oligocene–Miocene age and can be an ideal source of gas-saturated fluid. A significant amount of siderite minerals (FeCO₃) were collected from sediments at depths ranging from 0.5 to 327 cm below the lake floor (cmblf). An important feature of these carbonate minerals is the extremely strong enrichment in the heavy ¹³C isotope, reaching values of +33.3‰ VPDB. The δ¹³C of the siderite minerals, as well as their morphology and elemental composition, and the δ¹³C_DIC of the co-existing pore water, differed across layers of the core, which implies at least two generations of siderite formation. Here, we leverage mineralogical and geochemical data with 16S rRNA data from the microbial communities in sediments surrounding layers containing siderite minerals. Statistical data reveal the formation of three clusters of microbial communities based on taxonomical composition, key taxa among bacteria and archaea, and environmental parameters. Diversity and richness estimators decrease with sediment depth, with several similar prevailing clades located at the bottom of the core. Most of the taxa in the deep sediments could be associated with putative metabolisms involving organotrophic fermentation (Bathyarchaeia, Caldatribacteriota, and Chloroflexota). Various groups of methanogens (Methanoregulaceae, Methanosaetaceae, and Methanomassiliicoccales) and methanotrophic (Methanoperedenaceae) archaea are present in the sediment at variable relative abundances throughout the sampled depth. Based on the physicochemical characteristics of the sediment, carbon isotope analysis of carbonate minerals and DIC, and phylogenetic analysis of individual taxa and their metabolic potential, we present several models for subsurface siderite precipitation in Lake Baikal sediments.