Response of microbial communities of Lake Baikal to extreme temperatures

The survival rate, metabolic activity, and ability for growth of microbial communities of Lake Baikal after exposure to extremely low temperatures (freeze-thawing) for different lengths of time have been first studied. It has been shown that short-term freezing (1-3 days) inhibits the growth and activity of microbial communities. The quantity of microorganisms increased after 7- and 15-day freezing. In the periods of maximums, the total number of microorganisms in the test samples was twice as high as in the control. It was established that after more prolonged freezing the microorganisms required more time after thawing to adapt to new conditions. In the variants with 7- and 15-day freezing, the activities of defrosted microbial communities were three or more times higher than in the control. The survival rate and activity of Baikal microorganisms after freeze-thawing confirms the fact that the Baikal microbial communities are highly resistant to this type of stress impact.     

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.     

The Classification and the Monitoring of the State of Mouth Riverine and Lacustrine Ecosystems in Lake Baikal Based on the Composition of Local Microbiocenoses and Their Activity

The paper presents the results of the long-term investigation of microbial communities in the technogenically vulnerable mouth riverine and lacustrine ecosystems of Lake Baikal. The structural and functional parameters of the microbial communities were analyzed from the standpoint of developing destructive processes. The analysis showed that the total number of microorganisms (TNM), the number of saprophytic bacteria (NSB), and bacterial production (BP) were greater in the river-mouth water than in the near-mouth lake water. In the offshore direction, TNM and NSB decreased by a factor of 1.5 to 2, and BP decreased by a factor of 4 to 7. Based on TNM, NSB, and BP data, we classified the Lake Baikal rivers with respect to the degree of the impact of human activities on them. The degrading capability of the riverine microbial communities was found to be such that they degrade daily from tenths of a percent to 3.5% of the total amount of organic compounds polluting the river waters.     

Microbial community of the water column of the Selenga River-Lake Baikal biogeochemical barrier

The microbial communities of the estuarine zone and the mixing zone of river and lake waters in the Selenga River estuary were studied using the fluorescence in situ hybridization (FISH) method. The microorganisms belonging to the phylogenetic group Gammaproteobacteria were found to predominate in the river estuary, constituting up to 17% of the total bacterial community. Among cultivable microorganisms, organotrophic bacteria were predominant (2040 CFU/ml) in this zone, which results in high rates of microbial production (6.0 μg C/(l day). The microbial community structure changed with distance from the river estuary; representatives of the Alpha-, Beta-, and Gammaproteobacteria were present in equal proportions; psychrotolerant and oligotrophic bacteria were numerous. The rate of heterotrophic carbon dioxide assimilation decreased to 3.8 μg C/(l day). At 5–7 km from the river estuary, where the hydrologic, physical, and chemical conditions are similar to those of lake waters, members of the Betaproteobacteria, which are typical of the open waters of Lake Baikal, are the major representatives of planktonic microorganisms.     

The Biodiversity of Actinomycetes in Lake Baikal

The taxonomic analysis of 107 actinomycete strains isolated from the bottom sediments and water of Lake Baikal showed that most of the water isolates belong to the genus Streptomyces and most of the sediment isolates belong to the genus Micromonospora. In the sediments, the number of actinomycetes increased with depth (down to 200 m). Eight Streptomyces isolates were identified to a species level.     

Distribution of dissolved organic carbon in Lake Baikal and its watershed

 Concentrations of dissolved organic carbon (DOC) in Lake Baikal ranged from 90 to 110 μM C, considerably higher than those in oceanic environments. The DOC concentrations in the epilimnion were higher than those in the hypolimnion. Since particulate organic carbon (POC) concentrations in the pelagic waters of Lake Baikal were <10–40 μM C in the epilimnion and 2–5 μM C in the hypolimnion, DOC constitutes a major component of the organic carbon pool in Lake Baikal, especially in the deep layers. The DOC concentrations downstream of the Barguzin and Selenga Rivers were quite high (400–500 μM C). Probably because of the high concentrations of DOC in these rivers, the DOC levels in Barguzin Bay and offshore at the mouth of the Selenga River were higher than those in the pelagic regions of the central and south basins of Lake Baikal. The relationship between DOC and electric conductivity revealed the transport of DOC from rivers to the pelagic area in Lake Baikal. The spatial distribution of DOC suggested that a major part of DOC in the lake was allochthonous (land-derived). Received: July 26, 2002 / Accepted: September 16, 2002 Present address:Research Institute for Humanity and Nature, 335 Takashima-cho, Marutamachi Kawaramachi, Kamigyo-ku, Kyoto 602-0878, Japan Tel. +81-75-229-6167; Fax +81-75-229-6150 e-mail: yos@chikyu.ac.jp Acknowldgments The authors wish to thank Director Prof. M. Grachev and Dr. O. Timoshkin of the Limnological Institute, Siberian Branch, Academy of Science, Russia, for arranging the cruise on Lake Baikal. We are also indebted to Drs. V. Sinyukovich, I. Khanaev, and A. Zhdanov for their kind assistance during the expeditions. We wish to thank Ms. Y. Ito for measuring the DOC concentrations. This work was supported and financed by Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan (No. 09041159) and for Scientific Research of Priority Area B (No. 11213101) and by the International Geosphere-Biosphere Programme (IGBP) at Nagoya University. Correspondence to:T. Yoshioka     

Vertical planktonic structure in the central basin of Lake Baikal in summer 1999, with special reference to the microbial food web

Planktonic microbial interactions in the central basin of Lake Baikal were examined on a summer day in 1999. The subsurface maxima of bacterial abundance and chlorophyll concentration were recorded at the same depth, whereas the vertical distribution of heterotrophic nanoflagellates was the inverse of those of bacteria and picophytoplankton. Release of extracellular organic car-bon (EOC) from phytoplankton was estimated by the NaH¹⁴CO₃ method as 2.4µgCl^–1day^–1. Bacterial production (4.3µgCl^–1day^–1), estimated in a bottle incubation experiment using size-fractionated water samples, exceeded the EOC released. Thus, other supplying sources of organic matter are needed for the bacterial production. Grazing (2.6µgCl^–1day^–1) was also estimated in the experiment and accounted for 60% of the bacterial production. This is the first report on the microbial food web in the central basin of Lake Baikal.     

Local adaptation of microbial communities to heavy metal stress in polluted sediments of Lake Erie

Microbial communities must balance the assimilation of biologically necessary metals with resistance to toxic metal concentrations. To investigate the impact of heavy metal contaminants on microbial communities, we performed two experiments measuring extracellular enzyme activities (EEA) in polluted and unpolluted sediments of Lake Erie. In the first experiment, inoculations with moderate concentrations of copper and zinc appreciably diminished EEA from uncontaminated sites, whereas EEA from contaminated sediments increased or were only negligibly affected. In the second experiment, we compared the effects of three separate metals (i.e. copper, arsenic, and cadmium) on microbial community metabolism in polluted and unpolluted locations. Although copper and arsenic elicited differential effects by inhibiting EEA only in unpolluted sediments, cadmium inhibited EEA in both polluted and unpolluted sediments. Multivariate analyses of EEA from polluted sediments revealed direct associations among hydrolytic enzymes and inverse or absent associations between hydrolases and oxidases; these associations demonstrated resilience to heavy metal stress. In contrast, addition of heavy metals to unpolluted sediments appeared to have a higher impact on the multivariate pattern of EEA associations as revealed by an increase in the number of associations, more inverse relationships, and potential enzymatic trade-offs. The results of this study suggest community-level adaptations through the development of resistance mechanisms to the types and local levels of heavy metals in the environment.     

Abundance and composition of the summer phytoplankton community along a transect from the Barguzin River to the central basin of Lake Baikal

The abundance and composition of phytoplankton were investigated at six stations along a transect from the Barguzin River inflow to the central basin of Lake Baikal in August 2002 to clarify the effect of the river inflow on the phytoplankton community in the lake. The water temperature in the epilimnion was high near the shore at Station 1 (17.3°C), probably due to the higher temperature of the river water, and gradually decreased offshore at Station 6 (14.5°C). Thermal stratification developed at Stations 2–6, and a thermocline was observed at a 17–22-m depth at Stations 2–4 and an 8–12-m depth at Stations 5 and 6. The concentrations of nitrogen and phosphorus nutrients in the epilimnion at all stations were <1.0 μmol N l⁻¹ and <0.16 μmol P l⁻¹, respectively. Relatively high concentrations of nutrients (0.56–7.38 μmol N l⁻¹ and 0.03–0.28 μmol P l⁻¹) were detected in the deeper parts of the euphotic zone. Silicate was not exhausted at all stations (>20 μmol Si l⁻¹). The chlorophyll a (chl. a) concentration was high (>10 μg l⁻¹) near the shore at Station 1 and low (<3 μg l⁻¹) at five other stations. The <2 μm fraction of chl. a in Stations 2–6 ranged between 0.80 and 1.85 μg l⁻¹, and its contribution to total chl. a was high (>60%). In this fraction, picocyanobacteria were abundant at all stations and ranged between 5 × 10⁴ and 5 × 10⁵ cells ml⁻¹. In contrast, chl. a in the >2 μm fraction varied significantly (0.14–11.17 μg l⁻¹), and the highest value was observed at Station 1. In this fraction, the dominant phytoplankton was Aulacoseira and centric diatoms at Station 1 and Cryptomonas, Ankistrodesmus, Asterionella, and Nitzschia at Stations 2–6. The present study demonstrated the dominance of picophytoplankton in the pelagic zone, while higher abundance of phytoplankton dominated by diatoms was observed in the shallower littoral zone. These larger phytoplankters in the littoral zone probably depend on nutrients from the Barguzin River.     

非光合固碳微生物的碳源组合优化

二氧化碳(CO_2)过量排放而引起的全球变暖是目前全球面临的重大环境问题。微生物固碳是实现二氧化碳资源利用的一种重要方式。探索无需光照的高效固碳微生物对于更广泛环境条件下的微生物固碳具有重要意义。在从全球各大海域筛选富集出非光合微生物茵群的基础上,本文构建了在不同的电子供体条件下(铵和氢气)促进非光合微生物茵群生长的最佳混合碳源组合,得到如下结果:在以NH_4~+为电子供体的条件下,优化后的碳源组合为374.24 mgC/L碳酸钠(Na_2CO_3),54.76 mgC/L碳酸氢钠(NaHCO_3)和0 mgC/LCO_2时,最佳响应值TOC为3.06 mg/L。最佳响应值TOC低于以Na_2CO_3为单一碳源时,但高于以CO_2或NaHCO_3为单一碳源时;在以H_2为电子供体条件下,使用优化后的混合碳源为0.26 mg/L Na_2CO_3、0.59mg/L NaHCO_3和71.48mL/L CO_2时,非光合微生物菌群的固碳效率可达27.62 mg/L,较以CO_2为单一碳源提高35%左右。这可能意味着有H_2条件下非光合微生物菌群中的微生物可能以羟基丙酸固碳途径为主,而且多条固碳途径均能被混合菌群利用。     

Lipids and fatty acids of two pelagic cottoid fishes (Comephorus spp) endemic to Lake Baikal

Matured females of two Lake Baikal endemic fish species, Comephorus baicalensis and Comephorus dybowski, have been investigated for lipid of the whole body and specific tissues (liver, muscles, ovaries), phospholipid classes and fatty acids of neutral and polar lipids. Total lipid in the body (38.9% fresh weight), liver (23.5%) and muscles (14.5%) of C. baicalensis were greater than those of C. dybowski (4.7, 8.7 and 2.6%, respectively); only their ovaries were similar (5.3 and 5.6% lipid, respectively). In both species, phosphatidylcholine and phosphatidylethanolamine were the major phospholipids, ranging from 60.7 to 75.1% of total phospholipid and 14.5–25.7%, respectively. In most cases, monounsaturated fatty acids (MUFA) were the major fatty acid group in C. baicalensis, whereas polyunsaturated fatty acids (PUFA) were the major group in C. dybowski. The MUFA 18:1(n-9) prevailed over other fatty acids in C. baicalensis and varied from 19% in polar lipids of muscles to 56.1% in neutral lipids of muscles. In polar lipid of C. dybowski, the PUFA 22:6(n-3) prevailed over other fatty acids in muscles and ovaries, while 16:0 dominated polar liver lipids and neutral lipids of all tissues. Other major fatty acids included 16:1(n-7), 18:1(n-7), and 20:5(n-3). Values of the (n-3)/(n-6) fatty acid ratio for neutral lipids of C. baicalensis (0.5–0.9) are well below the range of values characteristic either for marine or freshwater fish, while these values for polar lipids (1.6–1.8) are in the range typical of freshwater fish. Neutral lipid fatty acid ratios in C. dybowski (2.5–3.1) allow it to be assigned to freshwater fish, but polar lipids (2.8–3.7) leave it intermediary between freshwater and marine fish.     

Aerobic Methanotrophic Communities in the Bottom Sediments of Lake Baikal

The results of the first systematical investigation into the aerobic methanotrophic communities inhabiting the bottom sediments of Lake Baikal have been reported. Use of the radioisotopic method revealed methane consumption in 12 10- to 50-cm-long sediment cores. The maximum methane consumption rates (495–737 µl/(dm³ day) were recorded in sediments in the regions of hydrothermal vents and oil and gas occurrence. Methane consumption was most active in the surface layers of the sediments (0–4 cm); it decreased with the sediment depth and became negligible or absent at depths below 20 cm. The number of methanotrophic bacteria usually ranged from 100 to 1000 cells/cm³ of sediment and reached 1 million cells/cm³ in the regions of oil and gas occurrence. The seventeen enrichment cultures obtained were represented mainly by morphotype II methanotrophs. Phylogenetic analysis of the enrichment cultures in terms of the amino acid sequence of the α subunit of the membrane-bound methane monooxygenase (MMO) revealed the predominance of methanotrophs of the genus Methylocystis. The results obtained suggest the presence of an active aerobic methanotrophic community in Lake Baikal.__________Translated from Mikrobiologiya, Vol. 74, No. 4, 2005, pp. 562–571.Original Russian Text Copyright © 2005 by Gainutdinova, Eshinimaev, Tsyrenzhapova, Dagurova, Suzina, Khmelenina, Namsaraev, Trotsenko.     

Osmotic and ionic hemolymph concentrations of bathyal and abyssal amphipods of Lake Baikal (Siberia) in relation to water depth

We studied the adaptive variations of the hemolymph concentrations in relation to water depth and pressure using deep-dwelling amphipods from Lake Baikal. Hemolymph osmolality was determined in six bathyal and abyssal species immediately after capture when values come closest to the habitat concentrations. In three species, hemolymph osmolalities correlated positively with depth of capture. Prevalent ions in the hemolymph are sodium and chloride. Lactate, our indicator for capture stress, was highest after trawling (2–6 mM) and lowest after retrieval from cages (0–0.6 mM). Acclimation to different pressure was studied by exposing the specimens to different water depths over several days. Hemolymph concentrations did not change after acclimation to surface pressure in the sublittoral Acanthogammarus albus, a native also to shallow water, but decreased by 30–80 mosmol/kg H₂O in the bathyal and abyssal species Acanthogammarus grewingki, Acanthogammarus reicherti, and Parapallasea lagowskii. Similarly, hemolymph osmolality decreased in A. reicherti and P. lagowskii originating from deep water, when acclimated to reduced water depth, and, in A. reicherti hemolymph osmolality reached its original high value when returned to the depth of capture. Higher hemolymph osmolalities and NaCl concentrations, demonstrated here for the first time, may provide selective advantages to abyssal species. Accepted: 24 August 2000     

A silica sands-based method for faithful analysis of microbial communities and DNA isolation from a wide range of species

A silica sands-based method has been developed to isolate high quality genomic DNAs from cells of animals, plants and microorganisms, such as Hemisalanx prognathus, Spinacia oleracea, Pichia pastoris, Bacillus licheniformis and Escherichia coli. To the best of our knowledge, no DNA isolation method has so wide application until now. In addition, this method and a commercially available kit were compared in analysis of microbial communities using high-throughput 16s rDNA sequencing. As a result, the silica sands-based method was found to be even more efficient in isolating genomic DNA from gram-positive bacteria than the kit, indicating that it would become a very valuable choice to faithfully reflect the composition of microbial communities.     

Response of marine microbial communities to anthropogenic stress

Marine microbial communities adapt rapidly to changingenvironmental conditions, including anthropogenicstress. Adaptation involves a wide range ofstrategies, including, (a) formation of resistant,dormant stages, (b) initiation of repair mechanisms, (c)immobilization of toxic chemicals, (d) active transportof chemicals out of the cell, (e) use of contaminantchemicals as carbon or energy sources, and (f)transformation of contaminants to less toxic or morevolatile forms.Adaptation responses are generally plasmid- orchromosomally-mediated and controlled throughinduction or derepression of a variety of biochemicalpathways. Characterization of microbial communityresponses at the molecular level provides biomarkersof contaminant exposure which in turn may be used toprovide an overall picture of ecosystem health. Thisreview will discuss the interactions betweenmicroorganisms and environmental contaminants and thepotential use of microbial biomarkers to assess thehealth of the microbial ecosystem.     

Response of microbial communities to elevated thallium contamination in river sediments

Abstract

The study of microbial communities in river sediments contaminated by thallium (Tl) is necessary to achieve the information for in-situ microbially mediated bioremediation. However, little is known about the microbial community in Tl-contaminated river sediments. In the present study, we characterized the microbial community and their responses to Tl pollution in river sediments from the Tl-mineralized Lanmuchang area, Southwest Guizhou, China. Illumina sequencing of 16S rRNA amplicons revealed that over 40 phyla belong to the domain bacteria. In all samples, Proteobacteria, Cyanobacteria, and Actinobacteria were the most dominant phyla. Based on the UPGMA (Unweighted Pair Group Method with Arithmetic Mean) tree and PCoA (Principal Coordinates Analysis) analysis, microbial composition of each segment was distinct, indicating in-situ geochemical parameters (including Tl, sulfate, TOC, Eh, and pH) had influenced on the microbial communities. Moreover, canonical correspondence analysis (CCA) was employed to further elucidate the impact of geochemical parameters on the distribution of microbial communities in local river sediments. The results indicated that a number of microbial communities including Cyanobacteria, Spirochaete, Hydrogenophaga, and Acinetobacter were positively correlated with total Tl, suggesting potential roles of these microbes to Tl tolerance or to biogeochemical cycling of Tl. Our results suggested a reliable location for the microbial community’s diversity in the presence of high concentrations of Tl and might have a potential association for in-situ bioremediation strategies of Tl-contaminated river. Overall, in situ microbial community could provide a useful tool for monitoring and assessing geo-environmental stressors in Tl-polluted river sediments.     

Assessing the vulnerability of endemic diatom species in Lake Baikal to predicted future climate change: a multivariate approach

Diatoms in Lake Baikal exhibit significant spatial variation, related to prevailing climate, lake morphology and fluvial input into the lake. Here we have assessed the threats to endemic planktonic diatom species (through the development of empirical models), which form a major component of primary production within the lake. Multivariate techniques employed include redundancy analysis (RDA) and Huisman–Olff–Fresco (HOF) models. Our analyses suggest that eight environmental variables were significant in explaining diatom distribution across the lake, and in order of importance these are snow thickness on the ice, water depth, duration of days with white ice, suspended matter in the lake, days of total ice duration, temperature of the water surface in July, concentration of zooplankton and suspended organic matter. Impacts on dominant phytoplankton diatom species are highlighted using t‐value biplots. Predictions of future climate change on Lake Baikal are likely to result in shorter periods of ice cover, decreased snow cover across the lake in spring, increased fluvial input into the lake, and an increase in the intensification of surface water stratification during summer months. All these factors are likely to impact negatively on the slow‐growing, cold‐water endemics such as Aulacoseira baicalensis and Cyclotella minuta, which currently dominate diatom assemblages. Instead, taxa that are only intermittently abundant, at present, in offshore areas (e.g. Stephanodiscus meyerii) are likely to become more frequent. However, given the climatic gradient across the lake, the timing and extent of changes in community structure are likely to vary. Moreover, palaeolimnological records show that Lake Baikal diatom assemblages have been dynamic throughout the Holocene, with both endemic and cosmopolitan species exhibiting periods of dominance. Effects of climate change on the entire lake ecosystem may yet be profound as the structure of the pelagic food web may change from one based on endemic diatom taxa to one dominated by nondiatom picoplankton, and as limnological functioning (e.g. stratification and mixing) affects deepwater oxygen availability, nutrient cycling and trophic linkages.     

Characterization of the depth-related changes in the microbial communities in Lake Hovsgol sediment by 16S rRNA gene-based approaches

The undisturbed sediment of Lake Hovsgol (Mongolia) is scientifically important because it represents a record of the environmental changes that took place between the Holocene (the present age) and Pleistocene (the last ice age; 12,000 14C years before present day). Here, we investigated how the current microbial communities change as the depth increases by PCR-denaturing gradient gel electrophoresis (DGGE) analysis of the 16S rRNA genes of the microbial communities. The microbial diversity, as estimated by the Shannon index, decreased as the depth increased. In particular, significant changes in archaeal diversity were observed in the middle depth (at 39-42 cm depth of total 60 cm depth) that marks the border between the Holocene and Pleistocene. Phylotype belonging to Beta-and Gamma-Proteobacteria were the predominant bacteria and most of these persisted throughout the depth examined. However, as the depth increased, some bacteria (some genera belonging to Beta-Proteobacteria, Nitrospira, and OP8-9) were not detectable while others (some genera belonging to Alpha-, Beta-, Gamma-Proteobacteria) newly detected by DGGE. Crenarchaea were the predominant archaea and only one phylotype belonging to Euryarchaea was found. Both the archaeal and bacterial profiles revealed by the DGGE band patterns could be grouped into four and three subsets, respectively, subsets that were largely divided by the border between the Holocene and Pleistocene. Thus, the diversity of the current microbial communities in Lake Hovsgol sediments decreases with increasing depth. These changes probably relate to the environmental conditions in the sediments, which were shaped by the paleoclimatic events taking place between the Holocene and Pleistocene.     

东湖水体的微生物污染状况初步调查

通过检测东湖的细菌总数、大肠杆菌与纤维素分解菌数目 ,发现东湖的细菌总数与大肠杆菌数目仍严重超标 ,前者为《生活饮用水卫生标准》GB5 74 9- 85的 2～ 99倍 ,后者为此标准的 1 0 0～ 1 0 0 0倍 ,但与一期截污工程完成初期相比已有很大改善 ,说明对东湖的污染治理取得初步成效。各湖区的细菌数目高度异质性 ,其规律与各湖区的有机碎屑数量呈正相关性