Diversity and Physiological and Biochemical Properties of Heterotrophic Bacteria Isolated from Lake Baikal Epilithic Biofilms

Microbiology - A total of 170 heterotrophic bacterial strains were isolated from Lake Baikal epilithic biofilms. Identification of the isolates was carried out using the 16S rRNA gene sequencing...     

On the vertical distribution of microorganisms in lake Baikal during spring deep-water renewal

The vertical distribution of microorganisms during spring deep-water renewal in Lake Baikal was studied. The downward advection of trophogenic waters was found to create conditions for the extensive growth of microorganisms capable of decomposing and mineralizing organic carbon, nitrogen, and phosphorus in deep water layers. These processes occur annually at spring thermal bars near the underwater slope of Lake Baikal, whereas in its pelagic zone, the deep intrusions of waters rich in organic material are observed only in the years when enhanced deep-water renewal is accompanied by a high spring yield of phytoplankton.     

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.     

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).     

Microbial Biodiversity in the Water of Lake Baikal

An investigation of the microbial community of Lake Baikal by the methods of general and molecular microbiology showed that culturable bacterial strains are represented by various known genera. The lake water contains a great number of bacterial morphotypes, as revealed by electron microscopy, and a great diversity of nonculturable microorganisms belonging to different phylogenetic groups, as revealed by 16S rRNA gene fragment sequencing. The inference is made that the microbial community of Lake Baikal contains not only known species but also new bacterial species that are possibly endemic to the lake.     

Microbial community of freshwater sponges in Lake Baikal

The microbial community of Baikal sponges has been studied in five species belonging to the genera Swartschewskia, Baicalospongia, and Lubomirskia of the endemic family Lubomirskiidae. The results show that the total numbers of bacteria and bacterioplankton production have an effect on the growth of L. baicalensis body. Bacteria of the genera Pseudomonas, Bacillus, Micrococcus, Sarcina, Flavobacterium, Arthrobacter, and Acinetobacter living in the sponges are representatives of the Baikal bacterioplankton. Actinomycetes of the genera Streptomyces and Micromonospora are a permanent component of the cultivable sponge microbial community. The numbers and enzyme activities of heterotrophic, oligotrophic, and psychrophilic bacteria isolated from different sponge species and from the ambient water in autumn and in winter have been estimated.     

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, δ-proteobacteria, β-proteobacteria (Nitrospirae), α-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).     

Investigation of distribution,species composition,and degree of resistance to antibiotics of the bacteria of the <Emphasis Type="Italic">Enterococcus</Emphasis> genus in Lake Baikal

The paper presents the result of investigation of species composition, distribution and degree of resistance to antibiotics of the Enterococcus bacteria in Lake Baikal. It is shown that they live in littoral zones of the lake. In the deep-water part of the lake the studied microorganisms are not found. We isolated 120 strains identified as E. faecium, E. avium, E. faecalis, E. mundii, E. hirae, E. durans, E. gallinarum. On the whole, the strains of enterococcus isolated from Lake Baikal are characterized as antibiotic-sensitive. Nevertheless, the antibiotic-resistant strains of enterococci are found in the studied collection, including those with typical intermediate level of resistance to vancomycin.     

Stratified distribution of nutrients and extremophile biota within freshwater ice covering the surface of Lake Baikal

Biological entities and gradients of selected chemicals within the seemingly barren ice layers covering Lake Baikal were investigated. Ice cores 40-68 cm long were obtained from in shore and offshore sites of Southern Lake Baikal during the cold period of a year (March-April) in 2007 and 2008. In microscopic observations of the melted ice, both algae and bacteria were found in considerable numbers (>10(3) cells/L and >10(4) cells/ml, respectively). Among all organisms found, diatom was generally the most predominant taxon in the ice. Interestingly, both planktonic and benthic algae were present in considerable numbers (2-4×10(4) cells/L). Dominant phototrophic picoplankton were comprised of small green algae of various taxa and cyanobacteria of Synechococcus and Cyanobium. The bacterial community consisted mostly of short rod and cocci cells, either free-living or aggregated. Large numbers of yeast-like cells and actinomycete mycelium were also observed. Concentrations of silica, phosphorus, and nitrate were low by an order of magnitude where biota was abundant. The profile of the ice could be interpreted as vertical stratification of nutrients and biomass due to biological activities. Therefore, the organisms in the ice were regarded to maintain high activity while thriving under freezing conditions. Based on the results, it was concluded that the freshwater ice covering the surface of Lake Baikal is considerably populated by extremophilic microorganisms that actively metabolize and form a detritus food chain in the unique large freshwater ecosystem of Lake Baikal.