Bacteriorhodopsin in a bloom of halobacteria in the Dead Sea

A dense bloom of red halobacteria developed in the Dead Sea in the summer 1980, bacterial densities of up to 1.9 x10⁷ cells ml^-1 were observed. The population consisted of two types: pleomorphic, cup-shaped cells and rod-shaped cells. A high content of bacteriorhodopsin was found in the bloom (up to 0.4 nmol per mg protein). The rod-shaped Halobacterium was isolated and was shown to contain bacteriorhodopsin.Abbreviations 20 specific gravity at 20°C - Tris Tris-(hydroxymethyl)-aminomethane     

Formation of manganese oxyhydroxides on the Dead Sea coast by alteration of Mn-enriched carbonates

Manganese enriched carbonates preferentially accumulate in near-shore, shallow water sediments of the Dead Sea. These carbonates are formed by coprecipitation of Mn with authigenic aragonite, as well as by direct precipitation of Mn-carbonate from the pore water of the shallow sediments. The primary source of the Mn that accumulates as carbonates is allochthonous Mn-enriched oxides that are eroded from the nearby coasts and become buried within the near-shore shallow water sediments. Due to the decline in the level of the Dead Sea between 1960–1990, bands of sediments (parallel to the current shoreline) which were previously submerged, became exposed to air and consequently desiccated. We suggest that in order to approach new hydraulic equilibrium in some of those coastal areas, the decline in the level of the lake was followed by a lakeward advance of fresher groundwater from the shallow coastal aquifer. Those fresher waters are characterized by a higher pH than the interstitial brine, and therefore a new state of water-rock interaction is established which results in oxidative alteration of Mn-carbonates to Mn-oxides. In addition, manganese-oxidizing bacteria, shown to be active in water with lower salinity than that of the Dead Sea, may also play a part in oxidation of divalent manganese released from the sediment. As a result, some segments of the Dead Sea coast are characterized by black Mn-enriched sediments that in places form crusts over the surface.     

Occurrence of virus-like particles in the Dead Sea

Electron-microscopic examination of water samples from the hypersaline Dead Sea showed the presence of high numbers of virus-like particles. Between 0.9 and 7.3 × 10⁷ virus-like particles ml⁻¹ were enumerated in October 1994 in the upper 20 m of the water column during the decline of a bloom of halophilic Archaea. Virus-like particles outnumbered bacteria by a factor of 0.9–9.5 (average 4.4). A variety of viral morphologies were detected, the most often encountered being spindle-shaped, followed by polyhedral and tailed phages. In addition, other types of particles were frequently found, such as unidentified algal scales, and virus-sized star-shaped particles. Water samples collected during 1995 contained low numbers of both bacteria and virus-like particles (1.9–2.6 × 10⁶ and 0.8–4.6 × 10⁷ ml⁻¹ in April 1995), with viral numbers sharply declining afterwards (less than 10⁴ ml⁻¹ in November 1995–January 1996). It is suggested that viruses may play a major role in the decline of halophilic archaeal communities in the Dead Sea, an environment in which protozoa and other predators are absent. Received: February 5, 1997 / Accepted: May 24, 1997     

Heavy metals in the Dead Sea and their coprecipitation with halite

After a prolongued period of stratification (about 300 years) the Dead Sea overturned in 1979 and again in 1982. Its waters became saturated with respect to halite and the massive precipitation of halite which occurred in winter 1982/83 has been monitored. We followed the fate of the heavy metals during this period of physical and chemical changes.The concentrations of Zn, Cd, Pb and Cu in the Dead Sea waters have been measured by anodic stripping voltammetry (ASV) which provided sensitive measurement of these elements after a minimal pretreatment of the samples (dilution 1: 1 and acidification). In the meromictic lake (prior to 1979), the concentrations of all four elements were larger in the deep anoxic layers. With the onset of halite precipitation a decline in their concentrations was observed. Most dramatic was the decrease in Cd, which practically disappeared from the water column in 1985. The coprecipitation of heavy metals with halite — collected by sediment traps in 1983 — was examined, as well as that of older halite recovered from a sediment core. Although concentrations of heavy metals were somewhat larger in recent halite, all halite samples had the same coprecipitation pattern: the concentration of Pb was the largest, followed by Cd, and that of Cu was the smallest. The apparent distribution coefficient was larger for Cd than for Pb.We estimated the amount of Cd which may have accompanied the deposition of halite during 1983–1985; it is compatible with its observed disappearance from the water column in 1985. The amounts of Pb and of Zn which are missing from the Dead Sea of 1985 are much larger than can be accounted for by coprecipitation with halite. A possible explanation is that the formation of halite crystals may have enhanced settling of particulates which in turn, may have scavenged Pb and Zn from the Dead Sea waters. Cu seems to be much less affected by the physical and chemical events which occurred in the Dead Sea during 1976–1985.     

Rhodospirillum sodomense,sp. nov., a Dead Sea rhodospirillum species

A new species of halophilic anoxygenic purple bacteria of the genus Rhodospirillum is described. The new organism, isolated from water/sediment of the Dead Sea, was vibrio-shaped and an obligate halophile. Growth was best at 12% NaCl, with only weak growth occurring at 6% or 21% NaCl. Growth occurred at Mg²⁺ concentrations up to 1 M but optimal growth was obtained at 0.05–0.1 M Mg²⁺. Bromide was well tolerated as an alternative anion to chloride. The new organism is an obligate phototroph, growing photoheterotrophically in media containing yeast extract and acetate or a few other organic compounds. Growth of the Dead Sea Rhodospirillum species under optimal culture conditions was slow (minimum t_d 20 h). Cells contained bacteriochlorophyll a and carotenoids of the spirilloxanthin series and mass cultures were pink in color. Absorption spectra revealed the presence of a B875 (light-harvesting I) but no B800/B850 (light-harvesting II) photopigment complex. The new organism shares a number of properties with the previously described halophilic phototrophic bacterium Rhodospirillum salinarum and was shown to be related to this phototroph by 16S rRNA sequencing. However, because of its salinity requirements, photosynthetic properties, and isolation from the Dead Sea, the new phototroph is proposed as a new species of the genus Rhodospirillum, R. sodomense.     

The sensitivity of halobacteria to antibiotics

Abstract Eleven species of the genera Halobacterium, Halococcus and the recently proposed Haloarcula were tested by the macro-broth dilution method for their sensitivity to 20 antibiotics with different modes of action. The most active were bacitracin, erythromycin, haloquinone, rifampicin and novobiocin. Resistant mutants of H. mediterranei to bacitracin, chloramphenicol and josamycin were obtained with frequencies of spontaneous mutation between 10⁻⁴ and 10⁻⁷.     

Nutrients in pore waters from Dead Sea sediments

Pore waters were separated from 50 cm-long cores of Dead Sea sediments raised from waters depths of 25, 30 and 318 m. The salinity of the pore water is close to that of the overlying water at 225–230 g l^–1 chloride. The titration alkalinity of the pore water is about 60 % of the overlying water, and sulfate is also depleted. Ammonia and phosphate concentrations are higher than those of the water column with up to 50 mg l^–1 N-NH₃ (ten times increase) and 350 µg l^–1 P-PO _inf4 ^sup3– (four to eight times increase). Early diagenetic reactions are a result of decomposition of organic matter and of water-sediment interactions, resulting in aragonite precipitation, phosphate removal to the sediments, probably by absorption on iron-oxyhydroxides followed by remobilization, reduction of sulfate and formation of iron sulfides and accumulation of ammonia. Mass balance calculations show that pore water contribute about 80% of the ammonia and 30% of the phosphate input into the Dead Sea water column. On the other hand, the sediments act as a sink for carbonate and sulfate.     

Assessment of Some Heavy Metals in the Dead Sea Mud and Treatment Optimization

This paper describes the experimental remediation of the Dead Sea mud and the quantitative determination of some heavy metals. Herein, two chelating agents were employed as extracting aqueous solution: ethylenediaminetetraacetic acid (EDTA) and citric acid. The study focused on the main known heavy metals that were reported previously to be in the Dead Sea mud, which are Co, Ni, Pb, Zn, and Cr. Findings had indicated that citric acid was efficient in the removal of the aforementioned heavy metals. Physicochemical parameters that were expected to affect the removal of metals in the Dead Sea mud were optimized. Those parameters were the chelating agent concentration, mixing time and speed, type of washing water, temperature, and pH. The results showed that the best removal of heavy metals from Dead Sea mud can be achieved under optimum citric acid concentration, 1.5 g/50 mL for treatment of 10 g mud. Optimum mixing speed and time were found to be 800 rpm and 1 hr, respectively. Regarding washing water, it was found that the use of the same water for repeated washing provided better removal percentages. pH values and temperature had effect on removal percentages of the heavy metals from mud. However, working at pH 7 and room temperature would provide convenient results for heavy metal removal.     

The Dead Sea — an economic resource for 10 000 years

The archaeological and historical record of the Dead Sea as an economic resource is longer than that of any other hypersaline lake. Although it is completely devoid of life, except for a few bacteria and algae, the climatic and geological conditions in the Dead Sea basin have produced circumstances which made this lake important for the economy of the area. The salt which was produced by evaporation of the water, or by quarrying from the salt diapir of Mt. Sodom, on the Dead Sea coast, is referred to in the Bible and in the Talmud. It was harvested until the 1930's. Potash has been extracted from the brine, by solar processes, since 1931 and today the Dead Sea is a major source of potash and bromine. The asphalt, which is found in seepages along the shores and in large blocks, occasionally found floating on the lake, has been used by the inhabitants of the area for waterproofing baskets and for decorative purpose, since the Pre-ceramic Neolithic Period, 10 000 years ago. Later, the asphalt became a major export item to Egypt. During the Early Bronze age, 4000 years ago, it was used mostly to glue flint implements to wooden handles and in the Graeco-Roman period it was used as one of the components in the embalming of Egyptian mummies. The area around the Dead Sea was the only source of balsam, perhaps the most important incense and medication of the Ancient World. Remains of a 7th century B.C. perfume factory, were found in Ein Gedi. During later periods, until the Arab conquest in the 7th century A.D., the growing of balsam was an imperial monopoly. The area of the Dead Sea was famous, for over 2000 years, for its dates and sugar. The therapeutical and medicinal properties of Dead Sea water and the hypersaline hot springs on its shore, were famous throughout the Ancient World. For example, King Herod the Great, 2000 years ago, used to visit the area to cure his many diseases. This practice continues today, and the lakes has become a major center for treatment of psoriasis. There is pictorial, archaeological and historical evidence to support the Dead Sea's importance as a trade artery for over 2300 years.     

The divalent cation requirement of the mitochondrial glycerol-3-phosphate dehydrogenase

Coupled respiration by blowfly mitochondria has been utilized to demonstrate an absolute divalent cation requirement for glycerol 3-phosphate respiration. With ADP, phosphate and EGTA, the respiration rate (state 3) decreases as a function of the amount of oxygen reduced, to approximately 15% of its maximum value, even at 40 mM dl-glycerol 3-phosphate; it can be increased to its maximum value by the addition of Ca²⁺, Sr²⁺ or Mn²⁺. The decline in state 3 rate is not due to the removal of membrane-bound calcium into the matrix by the calcium carrier, since it occurs in the presence of ruthenium red. The effect is energy-dependent since the state 3 respiration does not decrease in the presence of uncouplers. The increase in respiration upon the addition of calcium is not due to the energy-dependent calcium transport since it is sensitive to oligomycin and insensitive to ruthenium red.The divalent cation effector site is located on the glycerol-3-phosphate dehydrogense, since state 3 (or state 4) pyruvate-proline respiration (NAD-linked) is not affected by EGTA. Yet the state 3 pyruvate-proline respiration removes calcium so effectively from the glycerol-3-phosphate dehydrogenase in the presence of EGTA, that added calcium stimulates glycerol 3-phosphate (26.4 mM) respiration about 22-fold.Since uncouplers stimulate the inhibited glycerol 3-phosphate respiration only to a very small extent, a calcium stimulation of the rate of phenazine methosulfate reduction by glycerol 3-phosphate (26.4 mM) which bypasses all phosphorylation sites, should be detectable. Only a 3-fold stimulation was observed.The present experiments suggest that upon complete removal of divalent cations from the dehydrogenase, glycerol 3-phosphate does not act as a homotropic effector in the coenzyme Q reductase reaction.     

Dynamics of a bloom of halophilic archaea in the Dead Sea

After a period of more than ten years in which bacterial and algal community sizes were extremely small, a dense bloom of halophilic archaea developed in the upper 5–10 m of the Dead Sea water column in the summer of 1992. The development of this bloom followed a dilution of the upper water layer by winter rainfloods, which enabled the development of a short-lived dense bloom of the unicellular green alga Dunaliella parva. The dense archaeal community (up to 3.5 × 10⁷ cells m1^–1 in June 1992) imparted a red coloration to the Dead Sea, due to its high content of bacterioruberin. Bacteriorhodopsin was not detected. High levels of potential heterotrophic activity were associated with the bloom, as measured by the incorporation of labeled organic substrates. After the decline of the algal bloom, archaeal numbers in the lake decreased only little, and most of the community was still present at the end of 1993. The amount of carotenoid pigment per cell, however, decreased 2–3-fold between June 1992 and August 1993. No new algal and archaeal blooms developed after the winter floods of 1992–1993, in spite of the fact that salinity values in the surface layer were sufficiently low to support a new algal bloom. A remnant of the 1992 Dunaliella bloom maintained itself at the lower end of the pycnocline at depths between 7 and 13 m (September 1992–August 1993). Its photosynthetic activity was small, and very little stimulation of archaeal growth and activity was associated with this algal community.     

Production of d-lactate, acetate, and pyruvate from glycerol in communities of halophilic archaea in the Dead Sea and in saltern crystallizer ponds

Abstract When glycerol is added to cultures of halophilic archaea, especially representatives of the genera Haloferax and Haloarcula , massive amounts of acids are formed. HPLC and enzymatic analyses of supernatants of Haloferax cultures grown in the presence of glycerol showed that all produced d -lactate and acetate. Cultures of two Haloarcula species tested produced pyruvate and acetate from glycerol. In all cases only a small fraction of the added glycerol was converted to organic acids. Both lactate, pyruvate, and acetate can be used as substrates for the growth of many halophilic archaea, including those that produce them, and acid production is possibly an overflow phenomenon, due to the limited capacity of the enzymatic systems responsible for their dissimilation. To test whether lactate is formed also by natural communities of halophilic archaea at low glycerol concentrations such as may be encountered in situ, we incubated samples from the Dead Sea and from the saltern crystallizer ponds at Eilat with 1.5–3 μM [U-¹⁴C]glycerol. After depletion of the glycerol, around 10% of the label was found in lactate and acetate in both brine samples. In addition, pyruvate was formed in Dead Sea water. Upon further incubation of the Dead Sea samples after depletion of the glycerol, pyruvate disappeared rapidly, while acetate and lactate concentrations decreased only very slowly. In saltern brines the lactate formed was degraded after depletion of the glycerol, but the concentration of labelled acetate decreased only very slowly.     

A bloom of Dunaliella parva in the Dead Sea in 1992: biological and biogeochemical aspects

A bloom of the unicellular green alga Dunaliella parva (up to 15 000 cells m1^–1) developed in the upper 5 m of the water column of the Dead Sea in May-June 1992. This was the first mass development of Dunaliella observed in the lake since 1980, when another bloom was reported (up to 8800 cells m1^–1). For a bloom of Dunaliella to develop in the Dead Sea, two conditions must be fulfilled: the salinity of the upper water layers must become sufficiently low as a result of dilution with rain floods, and phosphate must be available. During the period 1983–1991 the lake was holomictic, hardly any dilution with rainwater occurred, and no Dunaliella cells were observed. Heavy rain floods in the winter of 1991–1992 caused a new stratification, in which the upper 5 m of the water column became diluted to about 70% of their former salinity. Measurements of the isotopic composition of inorganic carbon in the upper water layer during the bloom (¹³C = 5.1) indicate a strong fractionation when compared with the estimated –3.4 prior to the bloom. The particulate organic carbon formed was highly enriched in light carbon isotopes ( ¹³ C = – 13.5). The algal bloom rapidly declined during the months June–July, probably as a result of the formation of resting stages, which sank to the bloom. A smaller secondary bloom (up to 1850 cells m1–1) developed between 6 and 10 m depth at the end of the summer. Salinity values at this deep chlorophyll maximum were much beyond those conductive for the growth of Dunaliella, and the factors responsible for the development of this bloom are still unclear.     

Assessment of Heavy Metal Accumulation in Urban Soil around Potash Industrial Site in the East of the Dead Sea and their Environmental Risks

The aim of this study was to assess the extent and severity of metal contamination of soils in the east of the Dead Sea, southwestern Jordan. This area was affected by a potash plant and intensive agricultural production. The samples were obtained at two depths, 0–10 cm and 10–20 cm, and were analyzed by atomic absorption spectrophotometry for Cu, Fe, Zn, Mn, Pb, Cd, and Cr. Physicochemical parameters that are expected to affect the mobility of metals in the soil such as pH, TOM, CaCO₃, CEC, and conductivity were determined. The relatively high concentrations of metals in soils of the studied area were related to anthropogenic sources such as the potash industry, agricultural activities, and traffic emissions. The mean concentrations of the metals were of the order: C_Fe > C_Pb > C_Zn > C_Cr > C_Mn > C_Cu and C_Cd where C is the concentration of these metals in solution. Heavy metals such as Zn, Cd, and Pb showed higher concentrations in the area that is closer to the potash plant, while Cr concentration was low. These metals were concentrated in the soil surface and decreased in the lower part of soil due to their mobility, movement and physicochemical properties, and alkaline pH. Metals of anthropogenic origin, including Cd, Pb, and Zn, were highly enriched with respect to crustal composition. The non-clay minerals of the sand-sized fraction are composed mainly of quartz and calcite as major minerals, with dolomite and feldspar as minor minerals. Factor analysis revealed three groups of elements that differ in their distribution. The first of these components is unpolluted soil, which was distributed in the study area. The second is the polluted soil, which occurs mostly around the potash plant and Ghore El-Safi area. The third factor represents the physicochemical sources, and is not significant.     

A First Record of Obligate Halophilic Aspergilli from the Dead Sea

The isolation of obligate halophilic aspergilli from the Dead Sea and the range of salt tolerance of halophilic fungi isolated, are reported here for the first time. The mycobiota of the Dead Sea isolated in this study, was dominated by Aspergillus and Penicillium species; Cladosporium were found in lesser numbers. All three genera were obtained from the water sample; however, Aspergillus was the only genus obtained from the sediment. There was significant difference in growth of each isolate at different salt concentrations and intraspecies analysis revealed dissimilarity in response of strains to different salt concentrations in the growth medium The isolates were euryhaline, with halotolerance up to 20–25% solar salt, Aspergillus and Penicillium species showing a higher level of halotolerance, as compared to that of Cladosporium. Halophilic fungi were found in greater numbers in the sediment sample as compared to that in the water sample. Penicillium and Cladosporium species were exclusively facultative halophiles, while some species of Aspergillus were facultative halophiles. All the obligate halophiles isolated, belonged to the genus Aspergillus and were identified as A. penicillioides and A unguis, the latter being a first record of the species from the Dead Sea.     

Conversion of energy in halobacteria: ATP synthesis and phototaxis

Halobacteria are aerobic chemo-organotroph archaea that grow optimally between pH 8 and 9 using a wide range of carbon sources. These archaea have developed alternative processes of energy provision for conditions of high cell densities and the reduced solubility of molecular oxygen in concentrated brines. The halobacteria can switch to anaerobic metabolism by using an alternative final acceptor in the respiratory chain or by fermentation, or alternatively, they can employ photophosphorylation. Light energy is converted by several retinal-containing membrane proteins that, in addition to generating a proton gradient across the cell membrane, also make phototaxis possible in order to approach optimal light conditions. The structural and functional features of ATP synthesis in archaea are discussed, and similarities to F-ATPases (functional aspects) or vacuolar ATPases (structural aspects) are presented. Received: 18 December 1995 / Accepted: 3 April 1996     

Variability of Lipid Constituents of the Soil Cyanobacterium Microcoleus vaginatus from the Dead Sea Basin and Negev Desert

A study of lipids of the soil cyanobacterium Microcoleus vaginatus, which was isolated from microbial crusts collected in the Dead Sea basin and in the Negev desert, was performed. Twenty-six hydrocarbons and fatty acids were separated and identified by GC/MS using serially coupled capillary columns of different polarity. Changes in the lipid composition were evaluated by comparison of samples collected from different locations. Heptadecane, 1-heptadecene, 6- and 7-methylheptadecane, hexadecanoic and 9(Z)-octadecenoic acids were identified as the major constituents. Biochemical mechanisms of production of the different lipid compounds under UV irradiation are proposed.