New fish fossils from the Pliocene of Wadi Natrun, Egypt

New material from the Pliocene fish beds of Wadi Natrun, Egypt, is described, including a new species of Alestes (Characidae). A total of 15 freshwater and at least four marine genera are now known from the site. This fauna is reviewed with particular regard to the fossil history and zoogeographical relationships of its component taxa.     

Metagenomic Assessment of Prokaryotic Diversity within Hypersaline Tuz Lake,Turkey

Microbiology - Tuz Lake is the second biggest lake with an extreme hypersaline environment (over 32% (w/v) salt) in Turkey. It is reported that the lake was of marine origin, and its formation...     

Unexpected Diversity and Complexity of the Guerrero Negro Hypersaline Microbial Mat

We applied nucleic acid-based molecular methods, combined with estimates of biomass (ATP), pigments, and microelectrode measurements of chemical gradients, to map microbial diversity vertically on a millimeter scale in a hypersaline microbial mat from Guerrero Negro, Baja California Sur, Mexico. To identify the constituents of the mat, small-subunit rRNA genes were amplified by PCR from community genomic DNA extracted from layers, cloned, and sequenced. Bacteria dominated the mat and displayed unexpected and unprecedented diversity. The majority (1,336) of the 1,586 bacterial 16S rRNA sequences generated were unique, representing 752 species (≥97% rRNA sequence identity) in 42 of the main bacterial phyla, including 15 novel candidate phyla. The diversity of the mat samples differentiated according to the chemical milieu defined by concentrations of O₂ and H₂S. Bacteria of the phylum Chloroflexi formed the majority of the biomass by percentage of bulk rRNA and of clones in rRNA gene libraries. This result contradicts the general belief that cyanobacteria dominate these communities. Although cyanobacteria constituted a large fraction of the biomass in the upper few millimeters (>80% of the total rRNA and photosynthetic pigments), Chloroflexi sequences were conspicuous throughout the mat. Filamentous Chloroflexi bacteria were identified by fluorescence in situ hybridization within the polysaccharide sheaths of the prominent cyanobacterium Microcoleus chthonoplastes, in addition to free living in the mat. The biological complexity of the mat far exceeds that observed in other polysaccharide-rich microbial ecosystems, such as the human and mouse distal guts, and suggests that positive feedbacks exist between chemical complexity and biological diversity.     

The Wadi Natrun: Chemical composition and microbial mass developments in alkaline brines of Eutrophic Desert Lakes

Six lakes of the Wadi Natrun, Egypt, were studied with respect to the chemical composition of their brines and the occurrence of microbial mass developments. All investigated lakes showed pH values of approximately 11 and a total salt content of generally more than 30%. The main components were sulfate, carbonate, chloride, sodium, and minor amounts of potassium. Only traces of magnesium and calcium were present, but unusually high concentrations of organic carbon compounds, nitrogen compounds, and phosphate were found. Mass developments of phototrophic sulfur bacteria, halobacteria, cyanobacteria, and green algae were observed. The functions of complete nitrogen and sulfur cycles in the alkaline brines are discussed. The properties of the lakes and their ecology are compared with data on the Dead Sea and Great Salt Lake, Utah.     

Diversity, Activity, and Abundance of Sulfate-Reducing Bacteria in Saline and Hypersaline Soda Lakes

Soda lakes are naturally occurring highly alkaline and saline environments. Although the sulfur cycle is one of the most active element cycles in these lakes, little is known about the sulfate-reducing bacteria (SRB). In this study we investigated the diversity, activity, and abundance of SRB in sediment samples and enrichment cultures from a range of (hyper)saline soda lakes of the Kulunda Steppe in southeastern Siberia in Russia. For this purpose, a polyphasic approach was used, including denaturing gradient gel electrophoresis of dsr gene fragments, sulfate reduction rate measurements, serial dilutions, and quantitative real-time PCR (qPCR). Comparative sequence analysis revealed the presence of several novel clusters of SRB, mostly affiliated with members of the order Desulfovibrionales and family Desulfobacteraceae. We detected sulfate reducers and observed substantial sulfate reducing rates (between 12 and 423 μmol/dm³ day⁻¹) for most lakes, even at a salinity of 475 g/liter. Enrichments were obtained at salt saturating conditions (4 M Na⁺), using H₂ or volatile fatty acids as electron donors, and an extremely halophilic SRB, strain ASO3-1, was isolated. Furthermore, a high dsr gene copy number of 10⁸ cells per ml was detected in a hypersaline lake by qPCR. Our results indicate the presence of diverse and active SRB communities in these extreme ecosystems.     

Dissimilatory Arsenate and Sulfate Reduction in Sediments of Two Hypersaline, Arsenic-Rich Soda Lakes: Mono and Searles Lakes, California

A radioisotope method was devised to study bacterial respiratory reduction of arsenate in sediments. The following two arsenic-rich soda lakes in California were chosen for comparison on the basis of their different salinities: Mono Lake (~90 g/liter) and Searles Lake (~340 g/liter). Profiles of arsenate reduction and sulfate reduction were constructed for both lakes. Reduction of [⁷³As]arsenate occurred at all depth intervals in the cores from Mono Lake (rate constant [k] = 0.103 to 0.04 h⁻¹) and Searles Lake (k = 0.012 to 0.002 h⁻¹), and the highest activities occurred in the top sections of each core. In contrast, [³⁵S]sulfate reduction was measurable in Mono Lake (k = 7.6 ×10⁴ to 3.2 × 10⁻⁶ h⁻¹) but not in Searles Lake. Sediment DNA was extracted, PCR amplified, and separated by denaturing gradient gel electrophoresis (DGGE) to obtain phylogenetic markers (i.e., 16S rRNA genes) and a partial functional gene for dissimilatory arsenate reduction (arrA). The amplified arrA gene product showed a similar trend in both lakes; the signal was strongest in surface sediments and decreased to undetectable levels deeper in the sediments. More arrA gene signal was observed in Mono Lake and was detectable at a greater depth, despite the higher arsenate reduction activity observed in Searles Lake. A partial sequence (about 900 bp) was obtained for a clone (SLAS-3) that matched the dominant DGGE band found in deeper parts of the Searles Lake sample (below 3 cm), and this clone was found to be closely related to SLAS-1, a novel extremophilic arsenate respirer previously cultivated from Searles Lake.     

Abundance,Distribution, and Diversity of Viruses in Alkaline,Hypersaline Mono Lake,California

Mono Lake is a large (180 km²), alkaline (pH ~10), moderately hypersaline (70–85 g kg^–1) lake lying at the western edge of the Great Basin. An episode of persistent chemical stratification (meromixis) was initiated in 1995 and has resulted in depletion of oxygen and accumulation of ammonia and sulfide beneath the chemocline. Although previous studies have documented high bacterial abundances and marked seasonal changes in phytoplankton abundance and community composition, there have been no previous reports on the occurrence of viruses in this unique lake. Based on the high concentrations and diversity of microbial life in this lake, we hypothesized that planktonic viruses are also abundant and diverse. To examine the abundance and distribution of viruses and bacteria, water samples were collected from four stations along 5 to 15 vertical depths at each station. Viral abundance ranged from 1 × 10⁸ to 1 × 10⁹ mL^–1, among the highest observed in any natural aquatic system examined so far. Increases (p < 0.1) in viral densities were observed in the anoxic bottom water at multiple stations. However, regression analysis indicated that viral abundance could not be predicted by any single environmental parameter. Pulsed field gel electrophoresis revealed a diverse viral community in Mono Lake with genome sizes ranging from ~14 to >400 kb with most of the DNA in the 30 to 60 kb size range. Cluster analysis grouped the anoxic bottom-water viral community into a unique cluster differentiating it from surface and mid-water viral communities. A hybridization study using an indigenous viral isolate as a probe revealed an episodic pattern of temporal phage distribution with strong niche stratification between oxic and anoxic waters.     

Prokaryotic Community Compositions of the Hypersaline Sediments of Tuz Lake Demonstrated by Cloning and High-Throughput Sequencing

Microbiology - Tuz Lake is a shallow, perennial, inland hypersaline lake located at the center of the Turkey. Microbial populations developing in the sedimentary layers of the lake were...     

Morphological Characterization of Viruses in the Stratified Water Column of Alkaline, Hypersaline Mono Lake

Concentrations of viruses and prokaryotes in the alkaline, moderately hypersaline, seasonally stratified Mono Lake are among the highest reported for a natural aquatic environment. We used electron microscopy to test whether viral morphological characteristics differed among the epilimnion, metalimnion, and the anoxic hypolimnion of the lake and to determine how the properties of viruses in Mono Lake compare to other aquatic environments. Viral capsid size distributions were more similar in the metalimnion and hypolimnion of Mono Lake, while viral tail lengths were more similar in the epilimnion and metalimnion. The percentage of tailed viruses decreased with depth and the relative percentages of tailed phage families changed with depth. The presence of large (>125 nm capsid), untailed viruses in the metalimnion and hypolimnion suggests that eukaryotic viruses are produced in these suboxic and anoxic, hypersaline environments. Capsid diameters of viruses were larger on average in Mono Lake compared to other aquatic environments, and no lemon-shaped or filamentous viruses were found, in contrast to other high-salinity or high-altitude lakes and seas. Our data suggest that the physically and chemically distinct layers of Mono Lake harbor different viral assemblages, and that these assemblages are distinct from other aquatic environments that have been studied. Furthermore, we found that filtration of a sample through a 0.22-μm pore-size filter significantly altered the distribution of viral capsid diameters and tail lengths, resulting in a relative depletion of viruses having larger capsids and longer tails. This observation highlights the potential for bias in molecular surveys of viral diversity, which typically rely on filtration through 0.2- or 0.22-μm pore-size membrane filters to remove bacteria during sample preparation.     

Bacterial Diversity and Geochemical Profiles in Sediments from Eutrophic Azorean Lakes

In the Azores, the advanced trophic state of the lakes requires a fast intervention to achieve the good ecological status prescribed by the Water Framework Directive. Despite the considerable effort made to describe the phytoplankton growing on the water column, the lack of information regarding the microbial processes in sediments is still high. Thus, for the successful implementation of internal management actions, the present work explored the relationships between geochemical profiles and dominant members of the bacterial community in sediments from eutrophic Azorean lakes. Lake Azul geochemical profiles were quite homogeneous for all parameters, while in lake Furnas the total iron profile presented a peak below the aerobic layer. For lake Verde, the concentrations of all studied parameters (20 ± 2% loss-on-ignition; 2.10 ± 0.08 mg g^?1 total phosphorus; 1.31 ± 0.50 mg g^?1 total nitrogen; 8.06 ± 0.13 mg g^?1 total iron) in the uppermost sediment layer were approximately two times higher than the ones in sediments from other lakes, decreasing with sediment depth. The higher amounts of phosphorus and organic matter in lake Verde suggested a higher internal contribution of phosphorus to eutrophication. The dominant members of the sediment bacterial community, investigated by denaturing gradient gel electrophoresis, were mostly affiliated to Proteobacteria phylum (Alpha-, Delta-, and Gamma-subclasses), group Bacteroidetes/Chlorobi and phylum Chloroflexi. The Cyanobacteria phylum was solely detected in sediments from lake Verde and lake Furnas that presented the highest amounts of nitrogen and phosphorus both in the water column and sediments, while the other phyla were detected in sediments from the three studied lakes. In conclusion, management measurers to achieve the good ecological status until 2015 should be distinct for the different lakes taking into account the relative magnitude of the nutrient sources and the bacterial diversity in sediments.     

Structure of Microbial Communities of the Sediments of Alkaline Transbaikalia Lakes with Different Salinity

The goal of the work was to reveal the differences in the structure of microbial communities of Transbaikalia alkaline lakes stemming from the differences in their salinity and hydrochemical parameters. The lakes studied were Verkhnee Beloe (Buryat Republic, Russia), as well as Khilganta, Gorbunka, and Borzinskoe (Transbaikal krai, Russia) with salinity from 12.3 to 430 g/L, which differed in the mineral composition of the sediments and hydrochemical parameters. Lake sediments were found to contain 47 prokaryotic phyla (42 bacterial and 5 archaeal ones). The phyla Proteobacteria, Euryarchaeota, Bacteroides, Chloroflexi, Actinobacteria, and Firmicutes were predominant, comprising over 95% of the classified sequences. Comparative abundance of archaea increased with salinity from below 1% in Lake Verkhnee Beloe to 35% in Lake Borzinskoe. The most numerous bacterial OTUs belonged to gammaproteobacteria of the genus Halomonas (up to 15% of the number of classified sequences). The most numerous archaeal OTUs were identified at the genus level as members of the genera Halorubrum and Halohasta belonging to the family Halorubraceae, which comprises extremely halophilic Euryarchaeota.     

高盐盐湖可分离嗜盐耐盐菌的种群多样性及四氢嘧啶产量评价

为了解柴达木盆地茶卡盐湖、柯柯盐湖和小柴旦盐湖等三大硫酸镁亚型高盐盐湖可分离嗜盐耐盐菌的种群多样性,采用RM中、高盐培养基筛选分离可培养的嗜盐菌和耐盐菌,扩增16S rRNA基因序列进行种属鉴定和环境因子典范对应分析(CCA),选取优势菌属构建系统发育树,并采用高效液相色谱法(HPLC)检测次级代谢产物四氢嘧啶(Ect...     

Seasonal Variations of Chemical Composition of Water and Bottom Sediments in the Wetland of Wadi Gaza,Gaza Strip

Water and sediment samples were collected from 18 sampling stations in Wadi Gaza for two successive years in order to: (1) Establish a baseline condition of the geochemistry of surface water and sediments; (2) assess the impact of seasonal variation on distribution of heavy metals and major ions; and (3) identify possible natural and anthropogenic sources of pollution. The heavy metal concentrations in the sediments of the lake (downstream) were higher than those of the eastern eight stations(upstream) where the water was shallower. Shallower areas showed greater temporal variation than deeper areas. Several elements (P, Fe, Mn and As) showed the greatest temporal variability. For example, in the winter rainy season these elements decreased 2–10 times compared to their values in summer. Moreover, Ca, Na, Cl, PO₄, and NO₃ decreased3, 3, 5, 2, 4 times, respectively. Some of the trace metals were more abundant in these waters compared to the domestic wastewaters of the study area. The averages of Cd and Co were 6 and 43 μg/l, respectively and they were 50 times higher than the domestic wastewater results. The discharge of olive oil mill wastewater was recorded in the Ca, Na, Mg, K and P concentrations in sediments of one of the sampling stations.     

Distribution and Diversity of Archaea Corresponding to the Limnological Cycle of a Hypersaline Stratified Lake (Solar Lake, Sinai, Egypt)

The vertical and seasonal distribution and diversity of archaeal sequences was investigated in a hypersaline, stratified, monomictic lake, Solar Lake, Sinai, Egypt, during the limnological development of stratification and mixing. Archaeal sequences were studied via phylogenetic analysis of 16S rDNA sequences as well as denaturing gradient gel electrophoresis analysis. The 165 clones studied were grouped into four phylogenetically different clusters. Most of the clones isolated from both the aerobic epilimnion and the sulfide-rich hypolimnion were defined as cluster I, belonging to the Halobacteriaceae family. The three additional clusters were all isolated from the anaerobic hypolimnion. Cluster II is phylogenetically located between the genera Methanobacterium and Methanococcus. Clusters III and IV relate to two previously documented groups of uncultured euryarchaeota, remotely related to the genus Thermoplasma. No crenarchaeota were found in the water column of the Solar Lake. The archaeal community in the Solar Lake under both stratified and mixed conditions was dominated by halobacteria in salinities higher than 10%. During stratification, additional clusters, some of which may possibly relate to uncultured halophilic methanogens, were found in the sulfide- and methane-rich hypolimnion.     

Ecological resources for conservation and development in Wadi Allaqi,Egypt*

PULFORD, I. D., MURPHY, K. J., DICKINSON, G., BRIGGS, J. A. & SPRINGUEL, I., 1992. Ecological resources for conservation and development in Wadi Allaqi, Egypt. The creation of Lake Nasser behind the Aswan High Dam on the River Nile has brought about significant environmental changes in Upper Egypt. A multidisciplinary project was started in 1987 to assess the environmental changes associated with periodic inundation in desert ecosystems. The data presented here provide a baseline for studies aimed at assessing the potential for, and ecological impacts of, sustainable development in the target area, and may act as a blueprint for wider-scale development. Soil, water, vegetation, animal and human resources are being monitored. There has been a major increase in plant communities dominated by riverain species, at the expense of the original desert wadi vegetation. The water has attracted human settlement, with some 200–250 people now living in the wadi. The inherent high fertility of the soil has allowed them to grow a range of crops in small plots, using a system of shifting cultivation dictated by the lake water level. While this degree of development may be sustainable, larger-scale development of the fragile wadi ecosystem demands a full assessment of appropriate management techniques.     

An Anaerobic Methane-Oxidizing Community of ANME-1b Archaea in Hypersaline Gulf of Mexico Sediments

Sediments overlying a brine pool methane seep in the Gulf of Mexico (Green Canyon 205) were analyzed using molecular and geochemical approaches to identify geochemical controls on microbial community composition and stratification. 16S rRNA gene and rRNA clone libraries, as well as mcrA gene clone libraries, showed that the archaeal community consists predominantly of ANME-1b methane oxidizers; no archaea of other ANME subgroups were found with general and group-specific PCR primers. The ANME-1b community was found in the sulfate-methane interface, where undersaturated methane concentrations of ca. 100 to 250 μM coexist with sulfate concentrations around 10 mM. Clone libraries of dsrAB genes and bacterial 16S rRNA genes show diversified sulfate-reducing communities within and above the sulfate-methane interface. Their phylogenetic profiles and occurrence patterns are not linked to ANME-1b populations, indicating that electron donors other than methane, perhaps petroleum-derived hydrocarbons, drive sulfate reduction. The archaeal component of anaerobic oxidation of methane is comprised of an active population of mainly ANME-1b in this hypersaline sediment.     

Microbial Diversity in Maras Salterns, a Hypersaline Environment in the Peruvian Andes

Maras salterns are located 3,380 m above sea level in the Peruvian Andes. These salterns consist of more than 3,000 little ponds which are not interconnected and act as crystallizers where salt precipitates. These ponds are fed by hypersaline spring water rich in sodium and chloride. The microbiota inhabiting these salterns was examined by fluorescence in situ hybridization (FISH), 16S rRNA gene clone library analysis, and cultivation techniques. The total counts per milliliter in the ponds were around 2 × 10⁶ to 3 × 10⁶ cells/ml, while the spring water contained less than 100 cells/ml and did not yield any detectable FISH signal. The microbiota inhabiting the ponds was dominated (80 to 86% of the total counts) by Archaea, while Bacteria accounted for 10 to 13% of the 4′,6′-diamidino-2-phenylindole (DAPI) counts. A total of 239 16S rRNA gene clones were analyzed (132 Archaea clones and 107 Bacteria clones). According to the clone libraries, the archaeal assemblage was dominated by microorganisms related to the cosmopolitan square archaeon “Haloquadra walsbyi,” although a substantial number of the sequences in the libraries (31% of the 16S rRNA gene archaeal clones) were related to Halobacterium sp., which is not normally found in clone libraries from solar salterns. All the bacterial clones were closely related to each other and to the γ-proteobacterium “Pseudomonas halophila” DSM 3050. FISH analysis with a probe specific for this bacterial assemblage revealed that it accounted for 69 to 76% of the total bacterial counts detected with a Bacteria-specific probe. When pond water was used to inoculate solid media containing 25% total salts, both extremely halophilic Archaea and Bacteria were isolated. Archaeal isolates were not related to the isolates in clone libraries, although several bacterial isolates were very closely related to the “P. halophila” cluster found in the libraries. As observed for other hypersaline environments, extremely halophilic bacteria that had ecological relevance seemed to be easier to culture than their archaeal counterparts.