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.
Characterizing vertical profiles of water columns is important to understanding the biochemical cycles and nutrient dynamics of an aquatic ecosystem. Physical and chemical properties of surface water ...in Mongolian saline lakes have been studied over the past decade, but chemical composition along a vertical profile of the water column has not been well documented. Four major saline lakes (Lakes Telmen, Oigon, Tsegeen and Khag) in northwestern Mongolia were studied to determine geochemical behavior of microelements and to assess major ionic components and trace elements associated with vertical profile of various water samples and sediments. Water samples were vertically collected from each sampling depth with a vacuum deep-water sampler in July 2013. Physical–chemical parameters, major ionic components and trace elements were analyzed by conventional methods and inductively coupled plasma-mass spectrometry. Concentrations of microelements and mineralogical composition of sediment samples from near shore were characterized by X-ray fluorescence spectrometry and X-ray diffraction. This study was apparently the first to characterize chemical composition along vertical profiles of these lakes. Sodium, chloride and sulfate ions were largely conserved in all water samples except Lake Oigon. Depending on salinity type, these lakes were divided into sodium-sulfate lake (Lake Khag) or chloride lakes. Due to geomorphological characteristics, strontium (≤3.18 mg/l) was the only ion in the highest concentration across all depths of water and sediment samples among the lakes. Sediments were comprised mainly of quartz, anorthite, albite and orthoclase. In conclusion, physical and chemical properties in Lake Oigon were highly variable and dissimilar among lakes. Furthermore, we inferred that vertical profiles of water columns were intimately linked to variations in chemical composition of salt lakes in the western Mongolia.
Meromictic lakes are lakes that do not have intermixed layers, and thus have unique physical, chemical, and biological properties. Lake Oigon is one lake with such a meromictic nature. However, a ...detailed study of the physico-chemical characteristics of Lake Oigon hasn’t been conducted. In this study, we investigated the physico-chemical characteristics of the water of Lake Oigon from the surface to bottom at one-meter depth intervals and compared parameter trends in summer and winter. The predominant hydrochemical type of lake water was Na-Cl-SO4. The salinity of the lake’s water was mesosaline to hypersaline. The concentrations of major ions (except sulphate) and microelements in summer were lower than that in winter. The suboxic layers (chemocline), and anoxic layer (monimolimnion) were often rich in nitrate, sulphide, ammonium, and phosphate despite the season. We hope that this study will show the characteristics of this meromictic lake and provide underlying information for future research on the chemical composition of Lake Oigon.
Very few studies have attempted to profile the microbial communities in the air above freshwater bodies, such as lakes, even though freshwater sources are an important part of aquatic ecosystems and ...airborne bacteria are the most dispersible microorganisms on earth. In the present study, we investigated microbial communities in the waters of two high mountain sub-alpine montane lakes—located 21 km apart and with disparate trophic characteristics—and the air above them. Although bacteria in the lakes had locational differences, their community compositions remained constant over time. However, airborne bacterial communities were diverse and displayed spatial and temporal variance. Proteobacteria, Actinobacteria, Bacteroidetes, and Cyanobacteria were dominant in both lakes, with different relative abundances between lakes, and Parcubacteria (OD1) was dominant in air samples for all sampling times, except two. We also identified certain shared taxa between lake water and the air above it. The results obtained on these communities in the present study provide putative candidates to study how airborne communities shape lake water bacterial compositions and vice versa.
In recent years, climate change coupled with anthropogenic activities has led to monumental changes in saline lakes which are rapidly drying up across the globe and particularly in Central Asia. The ...landlocked country of Mongolia is rich in lakes which have remained primarily undisturbed by human impact, and many of these lakes have varying salinity regimes and are located across various geographical landscapes. In this study, we sampled 18 lakes with varying salinity regimes (hyperhaline, mesohaline, oligohaline, and polyhaline) covering 7000 km of western Mongolia and its various geographical landscapes (Gobi Desert, forests, and steppe). We identified that the bacterial communities that dominate these lakes are significantly influenced by salinity (
< 0.001) and geographical landscape (
< 0.001). Further, only five zOTUs were shared in all the lakes across the salinity regimes, providing evidence that both local and regional factors govern the community assembly and composition. Furthermore, the bacterial communities of hyperhaline lakes were significantly positively correlated with salinity (ANOVA,
< 0.001) and arsenic concentrations (ANOVA,
< 0.001), whereas bacterial communities of mesohaline and polyhaline lakes situated in forest and steppe landscapes were positively correlated with temperature (ANOVA,
< 0.001) and altitude (ANOVA,
< 0.001), respectively. Functional predictions based on the 16S rRNA gene indicated enrichment of KEGG Ontology terms related to transporters for osmoprotection and -regulation. Overall, our study provides a comprehensive view of the bacterial diversity and community composition present in these lakes, which might be lost in the future.
Microorganisms are critical to maintaining stratified biogeochemical characteristics in meromictic lakes; however, their community composition and potential roles in nutrient cycling are not ...thoroughly described. Both metagenomics and metaviromics were used to determine the composition and capacity of archaea, bacteria, and viruses along the water column in the landlocked meromictic Lake Shunet in Siberia. Deep sequencing of 265 Gb and high-quality assembly revealed a near-complete genome corresponding to
sp.
. in a viral sample and 38 bacterial bins (0.2-5.3 Mb each). The mixolimnion (3.0 m) had the most diverse archaeal, bacterial, and viral communities, followed by the monimolimnion (5.5 m) and chemocline (5.0 m). The bacterial and archaeal communities were dominated by
and
, respectively, whereas the viral community was dominated by
. The archaeal and bacterial assemblages and the associated energy metabolism were significantly related to the various depths, in accordance with the stratification of physicochemical parameters. Reconstructed elemental nutrient cycles of the three layers were interconnected, including co-occurrence of denitrification and nitrogen fixation in each layer and involved unique processes due to specific biogeochemical properties at the respective depths. According to the gene annotation, several pre-dominant yet unknown and uncultured bacteria also play potentially important roles in nutrient cycling. Reciprocal BLAST analysis revealed that the viruses were specific to the host archaea and bacteria in the mixolimnion. This study provides insights into the bacterial, archaeal, and viral assemblages and the corresponding capacity potentials in Lake Shunet, one of the three meromictic lakes in central Asia. Lake Shunet was determined to harbor specific and diverse viral, bacterial, and archaeal communities that intimately interacted, revealing patterns shaped by indigenous physicochemical parameters.
Jomthonic acid A (1), a new modified amino acid, was isolated from the culture broth of a soil-derived actinomycete of the genus Streptomyces. The structure and absolute configuration of 1 were ...determined by spectroscopic analyses and chemical conversion. Jomthonic acid A (1) induced differentiation of preadipocytes into mature adipocytes at 2-50 μM.
Microbial communities are considered to be functionally redundant, but few studies have tested this hypothesis empirically. In this study, we performed an in situ reciprocal transplant experiment on ...the surface and bottom waters of two lakes (Tsuei-Feng (T) and Yuan-Yang (Y)) with disparate trophic states and tracked changes in their microbial community composition and functions for 6 weeks using high-throughput sequencing and functional approaches. T lake's surface (Ts) and bottom (Tb) water active bacterial community (16S rRNA gene-transcript) was dominated by Actinobacteria, Bacteroidia, and Cyanobacteria, whereas Y lake's surface (Ys) and bottom (Yb) water had Gammaproteobacteria, Alphaproteobacteria, and Bacteroidia as the dominant classes. The community composition was resistant to changes in environmental conditions following the reciprocal transplant, but their functions tended to become similar to the incubating lakes' functional profiles. A significant linear positive relationship was observed between the microbial community and functional attributes (surface: R2 = 0.5065, p < 0.0001; bottom: R2 = 0.4592, p < 0.0001), though with varying scales of similarity (1-Bray Curtis distance), suggesting partial functional redundancy. Also, the entropy-based L-divergence measure identified high divergence in community composition (surface: 1.21 ± 0.54; bottom: 1.17 ± 0.51), and relatively low divergence in functional attributes (surface: 0.04 ± 0.01; bottom: 0.04 ± 0.01) in the two lakes' surface and bottom waters, providing further support for the presence of partial functional redundancy. This study enriches our understanding of community functional relationships and establishes the presence of partial functional redundancy in freshwater ecosystems.
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•Microbial communities are hypothesized to be functionally redundant.•In situ reciprocal transplant experiment to empirically test for functional redundancy•Community composition was resistant to changes in environmental conditions.•Functions tended to become similar to incubating environment's functional profile.•Partial functional redundancy in aquatic microbiome
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