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The Microbiology and Biogeochemistry of the Dead Sea
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The Dead Sea is a hypersaline water body. Its total dissolved salts content is on the average 322.6 gm/liter. The dominant cation is Mg (40.7 gm/liter), followed by Na (39.2 gm/liter), Ca (17 gm/liter) and K (7 gm/liter). The major anion is Cl (212 gm/liter), followed by Br (5 gm/liter); SO4 and HCO3, are very minor. The lake contains a limited variety of microorganisms and no higher organisms. The number of recorded species is very low, but the total biomass is reasonably high (about 105 bacteria/ml and 104 algal cells/ml). The indigenous flora is comprised mainly of obligate halophylic bacteria, such as the pink, pleomorphicHalobacterium sp., aSarcina-like coccus, and the facultative halophilic green alga,Dunaliella. Sulfate reducers can be isolated from bottom sediments. Recently a unique obligate magnesiophile bacteria was isolated from Dead Sea sediment. Several of the Dead Sea organisms possess unusual properties. TheHalobacterium sp. has extremely high intercellular K+ concentration (up to 4.8M) and extraordinary specificity for K+ over Na. TheDunaliella has very high intracellular concentration of glycerol (up to 2.1M). The microorganisms exert marked influence on some biogeochemical processes occurring in the lake, such as the control of the sulfur cycle and the formation and diagenesis of organic matter in the sediments. The Dead Sea is an excellent example of the development of two different mechanisms for adjusting to a hostile environment. The algae adjust to the high salinity by developing a mechanism for the exclusion of salts from the intracellular fluid and using glycerol for osmotic regulation. On the other hand, the bacteria adapt to the environment by adjusting their internal inorganic ionic strength, but not composition, to that of the medium. The problem of population dynamics and limiting factors for algal and bacterial productivity are discussed in view of the total absence of zooplankton and other consumers other than bacteria.
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... Several microorganisms found in the Dead Sea have distinct characteristics. The green microalga Dunaliella, which possesses a large cup-shaped chloroplast and no stiff cell wall, has an extremely high intracellular concentration of glycerol (up to 2.1 M) [58]. Halobacterium spp. ...
The Dead Sea is unique compared to other extreme halophilic habitats. Its salinity exceeds 34%, and it is getting saltier. The Dead Sea environment is characterized by a dominance of divalent cations, with magnesium chloride (MgCl2) levels approaching the predicted 2.3 M upper limit for life, an acidic pH of 6.0, and high levels of absorbed ultraviolet radiation. Consequently, only organisms adapted to such a polyextreme environment can survive in the surface, sinkholes, sediments, muds, and underwater springs of the Dead Sea. Metagenomic sequence analysis and amino acid profiling indicated that the Dead Sea is predominantly composed of halophiles that have various adaptation mechanisms and produce metabolites that can be utilized for biotechnological purposes. A variety of products have been obtained from halophilic microorganisms isolated from the Dead Sea, such as antimicrobials, bioplastics, biofuels, extremozymes, retinal proteins, colored pigments, exopolysaccharides, and compatible solutes. These resources find applications in agriculture, food, biofuel production, industry, and bioremediation for the detoxification of wastewater and soil. Utilizing halophiles as a bioprocessing platform offers advantages such as reduced energy consumption, decreased freshwater demand, minimized capital investment, and continuous production.
... Numerous scientists have demonstrated that microorganisms exist in all sorts of environments, but it is necessary to find suitable means to isolate them from understudied sites (Jacob et al. 2017;. For example, the Dead Sea was previously considered to be devoid of life, but today it is well understood that it contains living organisms (Nissenbaum 1975;Jacob et al. 2017). The microorganisms surviving in extreme conditions are called extremophiles, and there is a broad range of different extremophiles able to thrive under distinct conditions: high or low temperature, high or low pressure, high or low pH, radiation, elevated salty or ionic conditions, low water activity, and the presence of chelating ions or metals (Baker-Austin and Dopson 2007;Singh et al. 2019;Wang et al. 2013;Junge et al. 2011;Etten et al. 2022). ...
Extremophiles possess unique cellular and molecular mechanisms to assist, tolerate, and sustain their lives in extreme habitats. These habitats are dominated by one or more extreme physical or chemical parameters that shape existing microbial communities and their cellular and genomic features. The diversity of extremophiles reflects a long list of adaptations over millions of years. Growing research on extremophiles has considerably uncovered and increased our understanding of life and its limits on our planet. Many extremophiles have been greatly explored for their application in various industrial processes. In this review, we focused on the characteristics that microorganisms have acquired to optimally thrive in extreme environments. We have discussed cellular and molecular mechanisms involved in stability at respective extreme conditions like thermophiles, psychrophiles, acidophiles, barophiles, etc., which highlight evolutionary aspects and the significance of extremophiles for the benefit of mankind.
In Brazil, with the creation of the Arouca Law in 2009 and the need for substitutes for live animals in studies, it is essential to apply anatomical techniques to conserve corpses. Fixative substances prevent autolysis, facilitate incisions and make the protein fraction of the tissue insoluble, preserving its morphology due to antiseptic properties. Preservative solutions aim to maintain anatomical specimens intact to allow the long‐lasting use of them. Several techniques can promote such fixation and preservation, but formaldehyde is the most used in many countries. This research aims to determine the viability of a new anatomical technique using ethyl alcohol (EA) and formaldehyde, in different proportions, to fix canine cadavers and sodium chloride aqueous solution (SCAS 30%) for preservation biomechanical and microbiological analyses. Fresh samples were collected before fixation to be the control samples in every group. Corpses were divided into four groups: G1 (only formaldehyde), G2 (30% formaldehyde and 70% EA), G3 (70% formaldehyde and 30% EA) and G4 (50% formaldehyde and 50% EA) and were subsequently conserved in 30% SCAS. Analyses were done at D0 (before fixation), D30, D60, D90 and D120 after preservation on 30% SCAS. Biomechanical traction tests were performed on skin and jejunum samples at all times of fixation and preservation. Microbiological analyses of the solution were at the end of fixation and during all preservation moments. The control samples (fresh corpses) were compared to the other four groups with the T‐test. There was no statistical difference in the maximum rupture force (MRF) of the skin and jejunum between the control and the fixation and preservation moments. It was observed that G2 and G3 presented minor variations in the MRF with means of skin (−14.2 N) and jejunum (−0.28 N). There were significant differences at all times for rupture elongation (RE) of the skin and jejunum. G3 and G4 showed minor variations in the RE, with a difference between the skin (1.32 mm) and jejunum (0.23 mm). The microbiological analyses of the SCAS 30% did not show any contamination (aerobic and anaerobic microorganisms) for Groups 1, 2 and 3. For D120 of G4, Bacillus spp. was identified in the amount of 1.0 × 10.
Cyanobacteria exhibit a high level of morphological plasticity and physiological flexibility, which enables them to thrive in a wide range of environments. They are incredibly versatile and inhabit many different habitats on Earth, including extreme environments. Here, we discuss the diversity of halophilic and halotolerant cyanobacteria found in ecological niches, based on the microbiological culture-based data. We then review genome-resolved metagenomics and multi-omics evidence. These methods are powerful new tools that enable a more comprehensive understanding of cyanobacterial diversity. Metagenomics and multi-omics approaches have revealed the existence of previously unrecognized lineages of halophilic cyanobacteria and complement culture-based data in our understanding of cyanobacteria’s role in the ecology and evolution of life on Earth.
Alkaline lakes are among the most bioproductive aquatic ecosystems on Earth. The factors that ultimately limit productivity in these systems can vary, but nitrogen (N) cycling in particular has been shown to be adversely affected by high salinity, evidently due to the inhibition of nitrifying bacteria (i.e., those that convert ammonic species to nitrogen oxides). The coastal plain of Coorong National Park in South Australia, which hosts several alkaline lakes along 130 km of coastline, provides an ideal natural laboratory for examining how fine-scale differences in the geochemistry of such environments can lead to broad variations in nitrogen cycling through time, as manifest in sedimentary δ¹⁵N. Moreover, the lakes provide a gradient of aqueous conditions that allows us to assess the effects of pH, salinity, and carbonate chemistry on the sedimentary record. We report a wide range of δ¹⁵N values (3.8‰-18.6‰) measured in the sediments (0-35 cm depth) of five lakes of the Coorong region. Additional data include major element abundances, carbonate δ¹³C and δ¹⁸O values, and the results of principal component analyses. Stable nitrogen isotopes and wt% sodium (Na) display positive correlation (R² = 0.59, p < 0.001) across all lake systems. Principal component analyses further support the notion that salinity has historically impacted nitrogen cycling. We propose that the inhibition of nitrification at elevated salinity may lead to the accumulation of ammonic species, which, when exposed to the water column, are prone to ammonia volatilization facilitated by intervals of elevated pH. This process is accompanied by a significant isotope fractionation effect, isotopically enriching the nitrogen that remains in the lake water. This nitrogen is eventually buried in the sediments, preserving a record of these combined processes. Analogous enrichments in the rock record may provide important constraints on past chemical conditions and their associated microbial ecologies. Specifically, ancient terrestrial aquatic systems with high δ¹⁵N values attributed to denitrification and thus oxygen deficiency may warrant re-evaluation within the framework of this alternative. Constraints on pH as provided by elevated δ¹⁵N via ammonia volatilization may also inform critical aspects of closed-basin paleoenvironments and their suitability for a de novo origin of life.
p>Salinity is considered the most critical environmental factor which negatively affects the germination and growth of plants. In this study, the potential of using Dead Sea water (DS) as a seed priming agent for the mitigation of the adverse effects of salinity on seed germination and growth performance of wheat ( Triticum aestivum L.) was investigated. Germination of wheat seeds primed with different doses of DS; 0%, 5%, 10%, 15%, and 20% were evaluated under different saline conditions (0, 100, 200, and 300 mM NaCl). High salinity (300 mM NaCl) remarkably inhibited germination attributes and reduced seedling length. However, seeds primed with DS exhibited improved germination parameters and seedling growth. Among the different DS concentrations used, the 10% DS priming achieved the highest increase in final germination percentage tolerance, germination index, relative germination salt tolerance, and seedling length. The increased tolerance to salinity was associated with improved water imbibition, α-amylase activity, antioxidant capacity and osmotic homeostasis correlated with high proline and soluble sugar levels. In addition, DS priming increased the membrane stability index, and reduced malondialdehyde content and K+ leakage besides lowering Na+/K+ ratio. Overall, priming with DS could be a promising strategy for minimizing the damaging effects of salinity in wheat.</p
Despite intense research, methods for controlling soft matter’s spontaneous self-assembly into well-defined layers remain a significant challenge. We observed ion-induced structural discontinuities of phospholipid vesicles that can be exploited for controlled self-assembly of soft materials, using DOPC and NaCl as a model system. The observations were made for the 0.25 wt % lipid concentration. We used dynamic light scattering, zeta-potential measurement, cryo-electron microscopy, small-angle X-ray, and small-angle neutron scattering to understand the reason for the discontinuities. For salt concentrations below 8 mM, we observed a decrease in the liposome diameter with increased NaCl concentration. Above 8 mM, we measured a discontinuity; the radius increases within a very narrow salt concentration range within less than 0.1 mM and then decreases for values greater than 8 mM. At 75 mM, the radius becomes constant until it grows again at around 500 mM. Microscopy and scattering experiments show a transition from unilamellar to bilamellar at 8 mM and to trilamellar at 75 mM. At 500 mM, we found a heterogeneous liposome system with many different bilayer numbers. All the experimental observations indicate that declining solvent quality and increasing osmotic pressure direct lipids to expel preferentially to the inner compartment. Upon reaching a critical concentration, excess lipids can form a new bilayer. This spontaneous self-assembly process causes simultaneous shrinkage of the aqueous core and expansion of the vesicle. This approach opens an intriguing path for controlling the self-assembly of bioinspired colloids.
Abstract
Using narratives that I recorded in June/July 2021 on Kenya’s south coast with fishers belonging to three different generations, this paper provides insights into local articulations of changes that have happened in the sea over time. These changes — which call to mind ocean wealth and ocean health — have culminated in the increasing unproductivity of the ocean, which has led some shore folk to imagine that ‘the sea is dead’, as one of my interlocutors phrased it. What has caused the death of the sea? What does it mean for the sea to die? What will a dead ocean look like and what implications will it have for fishers? How are fishers responding to threats of a dying sea? By examining the local articulations of changes that are happening in the sea, I attempt answers to these questions. I also ask: How do the shore folk on the Kenyan coast account for these changes? In trying to seek answers to the factors underlying these changes, I am confronted with accounts of rituals that have been discontinued and find that these discontinued rituals have been put forth as explanations for the changes in question, most of which are negative.
The origin of eukaryotic cells, and especially naturally occurring syncytial cells, remains debatable. While a majority of our biomedical research focuses on the eukaryotic result of evolution, our data remain limiting on the prokaryotic precursors of these cells. This is particularly evident when considering extremophile biology, especially in how the genomes of organisms in extreme environments must have evolved and adapted to unique habitats. Might these rapidly diversifying organisms have created new genetic tools eventually used to enhance the evolution of the eukaryotic single nuclear or syncytial cells? Many organisms are capable of surviving, or even thriving, in conditions of extreme temperature, acidity, organic composition, and then rapidly adapt to yet new conditions. This study identified organisms found in extremes of salinity. A lake and a nearby pond in the Ethiopian Rift Valley were interrogated for life by sequencing the DNA of populations of organism collected from the water in these sites. Remarkably, a vast diversity of microbes were identified, and even though the two sites were nearby each other, the populations of organisms were distinctly different. Since these microbes are capable of living in what for humans would be inhospitable conditions, the DNA sequences identified should inform the next step in these investigations; what new gene families, or modifications to common genes, do these organisms employ to survive in these extreme conditions. The relationship between organisms and their environment can be revealed by decoding genomes of organisms living in extreme environments. These genomes disclose new biological mechanisms that enable life outside moderate environmental conditions, new gene functions for application in biotechnology, and may even result in identification of new species. In this study, we have collected samples from two hypersaline sites in the Danakil depression, the shorelines of Lake As’ale and an actively mixing salt pond called Muda’ara (MUP), to identify the microbial community by metagenomics. Shotgun sequencing was applied to high density sampling, and the relative abundance of Operational Taxonomic Units (OTUs) was calculated. Despite the broad taxonomic similarities among the salt-saturated metagenomes analyzed, MUP stood out from Lake As’ale samples. In each sample site, Archaea accounted for 95% of the total OTUs, largely to the class Halobacteria. The remaining 5% of organisms were eubacteria, with an unclassified strain of Salinibacter ruber as the dominant OTU in both the Lake and the Pond. More than 40 different genes coding for stress proteins were identified in the three sample sites of Lake As’ale, and more than 50% of the predicted stress-related genes were associated with oxidative stress response proteins. Chaperone proteins (DnaK, DnaJ, GrpE, and ClpB) were predicted, with percentage of query coverage and similarities ranging between 9.5% and 99.2%. Long reads for ClpB homologous protein from Lake As’ale metagenome datasets were modeled, and compact 3D structures were generated. Considering the extreme environmental conditions of the Danakil depression, this metagenomics dataset can add and complement other studies on unique gene functions on stress response mechanisms of thriving bio-communities that could have contributed to cellular changes leading to single and/or multinucleated eukaryotic cells.
The first analysis of Dead Sea water was done in 1778. The progress in the science of analytical chemistry is reflected in the improved procedures used for analysis of Dead Sea water. The first analysis by Macquer, Lavoisier and Sage (1781) noted most of the unusual chemical properties of the lake. The earliest search for life in the Dead Sea was made by Gay Lussac in 1817 while trace element analysis goes back to 1827. Some of the early investigators suggested that most of the salt content is contributed by the Jordan River, accompanied by precipitation of CaCO3 and CaSO4. This hypothesis is now accepted by many investigators.
One of the most remarkable characteristics of certain marine algae is their ability to survive and to withstand changes in the osmotic concentration of seawater. Certain marine algae tolerate salt concentrations ranging from 0.1 to 3.0 times that of seawater (BIEBL, 1952; BIEBL, 1958; EPPLEY and CYRUS, 1960). In nature the phenomenon of marine algal osmotic tolerance toward large changes in salinity is often associated with intertidal habitats and salt lakes.
Extreme halophilism is regarded as a unique phenomenon in the living world. The organisms possessing this phenomenon serve as very valuable objects in the study of basic problems in molecular biology. Their extremeness offers a possibility to apply the concept of comparative biochemistry. The red-colored bacteria living in very salty environment are considered to be highly specialized organisms. These bacteria manage to live and proliferate in concentrated sodium chloride brine and require very strong—almost saturated — salt brine for best maintenance and growth. This property is essentially referred as “extreme halophilism” and is found only among the bacteria. This chapter describes extreme halophilism, their growth relations, metabolic apparatus of the extreme halophiles, and cell envelope of the halobacteria. In context to extreme halophiles, the study of protein synthesis is regarded particularly important because of the unusual properties of the protein components in these organisms. The cell envelope of the halobacteria is another important object and its apparent simplicity can be of great value in the elucidation of cell envelope structure, synthesis, and functions.
Reducing surface sediment from a depth of 300 m in the Dead Sea was found to contain phytanic acid (520 μg/Kg), dihydrogen phytol (800 μg/Kg) and phytane (17 μg/Kg). An investigation revealed that glycerol phytanyldiether could be isolated from the sediment by hydrolysis of a lipid soluble fraction. The phytanyldiether is probably derived from the phosphatidyl glycerophosphate lipid, which has been demonstrated by Kates and co‐workers to be the dominant lipid present in red halophilic bacteria. Comparison of results by analysis of Halobacterium cutirubrum, using the same analytical procedure as was used for the sediment investigation, confirmed the authenticity of the lipid characterization. In view of this finding, it is suggested that phytane in the Dead Sea sediment has been derived from this lipid and that long‐chain isoprenoid hydrocarbons in some ancient environments may have had a similar origin.
Studies were performed to determine the distribution of microbiota in the Dead Sea during 1963 to 1965. The dominant organisms in the surface water were found to be two red halophilic bacteria, followed in abundance by a green flagellated alga, Dunaliella virdis. Cultures inoculated with Dead Sea water produced growth of the red bacteria as well as unidentified non-pigmented halo-tolerant bacteria, capable of growing in 25% salt solution, and bacteria that grew only in dilute salt media. The latter are mainly spore-forming aerobes, probably introduced by rain-wash of the soil, as well as from the Jordan River and fresh water springs. Sulfate reducing bacteria were also cultured from the water and from the sediment. Pigment studies on extracts from laboratory cultures of the red bacteria, from centrifuged suspensions of Dead Sea water and, by comparison, from a pure culture of Halobacterium salinarium, showed that the dominant pigment in all cases was the carotene α-bacteriorubrin. The total number of organisms decreased with depth of the water column, especially below the thermocline. The interpretations given for the decrease are: lack of dissolved oxygen, decrease in incident light, and lack of dissolved phosphate. The last factor is probably due to rapid precipitation of phosphate by divalent ions.