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The genus Methylomarinum accommodates aerobic motile non-pigmented methanotrophic bacteria, which were isolated from marine habitats and require NaCl for growth. Until recently, this genus contained a single species, M. vadi. Here, we describe a novel Methylomarinum representative, strain Ch1-1T, obtained from the sediments of the River Chernavka at its confluence with the hypersaline Lake Elton, Russia. Strain Ch1-1T was represented by gram-negative, pink-pigmented, motile rods or ovoids, which multiplied by binary fission and possessed the particulate methane monooxygenase (pMMO). These bacteria grew on methane within the temperature range of 5–42°C (optimum at 30–35°C) and at рH 6.3–7.5 (optimum at 6.5–6.8). Growth on methanol was inconsistent. NaCl was required for growth, which was observed in liquid media only within a NaCl concentration range of 0.5–10% (w/v). Best growth was recorded at a NaCl concentration of 3.5–4.0% (w/v). The 16S rRNA gene sequence of strain Ch1-1T displayed 97.09–97.24% similarity to the corresponding gene fragments of described representatives of M. vadi. The genome of strain Ch1-1T was 4.8 Mb in size and contained 3 rRNA operons and about 4400 protein-coding genes, including the gene cluster pmoCAB coding for pMMO, a complete set of genes for the function of the ribulose monophosphate pathway as well as genes necessary for ectoine and sucrose biosynthesis. The DNA G+C content was 50.7 mol %. The average nucleotide identity determined for genomes of strain Ch1-1T and M. vadi IT-4T was 78.8%. Based on the number of genotypic and phenotypic differences, we propose to classify this isolate as representing a novel species of the genus Methylomarinum, M. roseum sp. nov. strain Ch1-1T (=VKM B-3852T = UQM 41855T) is the type strain of the newly proposed species. [ABSTRACT FROM AUTHOR]

Polyhydroxyalkanoates (PHAs), green alternatives to petroleum-derived plastics, possess desired features that make them preferred for various applications. Poly(3-hydroxybutyrate) (PHB), one of the most known representative of PHAs, could be synthesized by haloarchaeal species but their production amounts are relatively low compared to those of poly(3-hydroxybutyrate-co-hydroxyvalerate) (PHBV) obtained by haloarchaea. This is the first report describing an overproduction of PHB by a wild-type halophilic archaeon isolated from southern Tunisia, Chott El Jerid. According to the 16S rRNA gene sequence analysis, the isolate CEJ40-10 was affiliated with the species of the genus Haloarcula (97.5% similarity). Regarding the phylogeny based on the amino acid sequences of the PHA synthase subunits encoded by phaC and phaE, their identities to those from Haloarcula quadrata were 99% and 100%, respectively. This strain could accumulate maximum PHA using 1% (w/v) starch at pH 6, after incubation for 72 h at 37 °C with high salt content (30% NaCl). The replacement of starch with glucose or sugar wastewater lowered the polymer yield. Four extraction methods were performed in order to achieve the maximum efficiency of polymer recovery. Hypochlorite digestion of biomass gave a high recovery yield, reaching 72.8% of its total dry mass. Furthermore, analytical methods such as the Fourier transform infrared (FTIR) spectroscopy, gas chromatography (GC), and UV–visible spectrophotometry indicated that the composition of the polymer was a homopolymer PHB. Our findings showed that Haloarcula sp. strain CEJ40-10 was a potential PHB-candidate for industrial scale production using starchy substrates. [ABSTRACT FROM AUTHOR]

The study presents a multi-proxy archive from hypersaline coastal Lake Chokrak in eastern Crimea, a steppe region which is particularly susceptible to moisture fluctuations. XRF, organic carbon and nitrogen, and palynological analyses are used to reconstruct the evolution of the lake and landscape development around it and to provide information about the driving forces behind those changes, such as climate and human impact. The findings show that the basin was an open marine bay between 7640 and 5500 cal. yr BP. After 5500 cal. yr BP, the low rates of sea-level rise led to gradual infilling of the basin. The prevalence of mesic herb-grass steppe around the site, as well as the expansion of broad-leaved trees in the Crimean mountains, indicate relatively warm and humid climate conditions during the Mid-Holocene. Elemental proxies and marine NPPs point to a transition to lagoonal conditions from 4270 cal. yr BP. The progressive shallowing of the basin was accompanied by the spread of more xeric Artemisia -grass steppe, which suggests a shift to arid conditions. The occurrence of cereal pollen from 3660 cal. yr BP may indicate the first signs of cultivation in the study area. The active build-up of a sand barrier from 3000 cal. yr BP led to a gradual separation of the basin from the sea. By 900 cal. yr BP, the fully-formed sand barrier resulted in a transformation of the lagoon into a hypersaline lake. The closing of the lagoon was accompanied by an expansion of halophytic communities around the site. Human-induced vegetation changes became more pronounced with the development of agrarian and pastoral activities around the site from ca. 750 cal. yr BP. [ABSTRACT FROM AUTHOR]

Urmia Lake in NW Iran was the world’s second largest hypersaline lake until three decades ago, when it began to lose ~ 90% of its surface area due to dwindling water input and enhanced evaporation. To help discern the role of natural vs anthropogenic factors in the rapid demise of Urmia Lake, we present a high-resolution, multi-proxy reconstruction of climate, and hydrological variability from the lake’s sediments. We identify several episodes of wet and dry conditions over the past 11,300 years, and an atmospheric teleconnection between the climate of the interior of West Asia and the North Atlantic region. Estimates of mean annual precipitation based on chemical weathering indices range between 174 and 401 mm year−1 during the Holocene. A combination of geochemical proxies, pollen reconstruction, and the absence of any evaporite horizons throughout the Holocene period point to the prevailing role of human impact on the current vanishing of Urmia Lake. [ABSTRACT FROM AUTHOR]

Meromictic lakes do not mix entirely due to a strong saline gradient that separates the mixolimnion (superficial, less saline) from the monimolimnion (deep, more saline). The East lagoon of the Parque Luro Provincial Reserve (La Pampa) is a typical hypersaline (salitral) lagoon that, after an exceptional rainfall, was transformed into a shallow meromictic lake. The present work aimed to survey the changes in the physicochemical characteristics in the water and in the planktonic communities during meromixis, which lasted at least 7 months. Compared to the monimolimnion, the mixolimnion was characterized by lower salinity and nutrients; however, it had higher pH, dissolved oxygen, chlorophyll, and suspended organic solids. The shallow depth of this lake and the action of the winds caused the end of the meromixis. Phytoplankton was dominated almost exclusively by Dunaliella salina and during meromixis, no differences in density or biomass were observed in its vertical distribution. Zooplankton (generally dominated by Artemia persimilis) decreased in richness with increasing salinity. During meromixis, this species coexisted with Boeckella poopoensis, and both had high densities of juveniles in the mixolimnion relative to the monimolimnion. The episode of a short meromixis, as described in this study, allowed the observation of diverse limnological conditions and the development of a greater number of zooplankton species, some endemic to the region. These attributes make this shallow lake a site of particular conservation interest. [ABSTRACT FROM AUTHOR]

Abstract Lake Hillier is a hypersaline lake known for its distinctive bright pink color. The cause of this phenomenon in other hypersaline sites has been attributed to halophiles, Dunaliella, and Salinibacter, however, a systematic analysis of the microbial communities, their functional features, and the prevalence of pigment-producing-metabolisms has not been previously studied. Through metagenomic sequencing and culture-based approaches, our results evidence that Lake Hillier is composed of a diverse set of microorganisms including archaea, bacteria, algae, and viruses. Our data indicate that the microbiome in Lake Hillier is composed of multiple pigment-producer microbes, including Dunaliella, Salinibacter, Halobacillus, Psychroflexus, Halorubrum, many of which are cataloged as polyextremophiles. Additionally, we estimated the diversity of metabolic pathways in the lake and determined that many of these are related to pigment production. We reconstructed complete or partial genomes for 21 discrete bacteria (N = 14) and archaea (N = 7), only 2 of which could be taxonomically annotated to previously observed species. Our findings provide the first metagenomic study to decipher the source of the pink color of Australia’s Lake Hillier. The study of this pink hypersaline environment is evidence of a microbial consortium of pigment producers, a repertoire of polyextremophiles, a core microbiome and potentially novel species.

The results of studying the influence of the main natural environmental factors on the interannual (2017–2021) and seasonal (from April to October) zooplankton dynamics of the large hypersaline Lake Kulunda located in the Kulunda steppe (Altai krai, Russia) are presented. The relationship of 13 main indicators of the structure of zooplankton (number and biomass in total, the main taxonomic groups: rotifers, copepods, cladocerans, and branchiopods, as well as different stages of the life cycle of Artemia) with the main hydrophysical and hydrochemical indicators (temperature, density, salinity, and pH of water) was analyzed separately by monthly and average annual (for the growing season) values. The influence of the studied factors on the characteristics of the brine shrimp population (number, biomass, and age structure), which dominated the zooplankton of this lake, was analyzed in more detail. It was revealed that the hydrophysical and hydrochemical regimes of the lake in different years are subject to significant changes and are reflected in the indicators of zooplankton. Changes in the structure of zooplankton under the influence of natural factors are mainly due to the stimulating effect of an increase in water mineralization on the Artemia population and its depressing effect on the brackish fauna. With a decrease in water salinity less than 100 g/dm3 since 2017 (127 g/m3) to 2021 (96 g/dm3) maximum (summer) Artemia biomass decreased from 167 to 17.7 g/m3. At the same time, the maximum biomass of rotifers, cladocerans, and copepods increased from 0.003, 0, and 0.63 to 6.21, 1.35, and 2.65 g/m3 respectively. [ABSTRACT FROM AUTHOR]

Saline and hypersaline waters are one of the most peculiar ecosystems of our planet, characterized by extreme life conditions. Despite their worldwide distribution, the diversity and abundance of protist communities in these ecosystems remain poorly studied. Here, we analyze planktonic communities of protists sampled across 38 saline and hypersaline water environments (2–390‰) from arid climatic zones of the South Urals and Crimea in light of environmental data using high-throughput 18S rDNA amplicon sequencing. A total of 9 eukaryotic supergroups, 34 phyla, 104 classes, 184 orders, 315 families and 548 genera have been identified. We revealed significant differences in the taxonomic structure of protist communities depending on salinity, geographic location and pH. The protist communities demonstrated linear regression of richness and diversity and growth of the percentage of unclassified Eukaryota (up to 43%) with the increase in salinity. Centrohelids demonstrated the ability to inhabit a broad range of salinities, up to 320‰, which is four times higher than previously reported. Centrohelid species Pinjata ruminata and Yogsothoth sp. are assumed to be specifically adapted to salinity of 3–210‰. The obtained results provide insight into the taxonomy and diversity of protists in saline and hypersaline environments and highlight the great potential for the discovery of new taxa due to the large number of unclassified 18S rDNA sequences. [ABSTRACT FROM AUTHOR]

Lake Hillier is a hypersaline lake known for its distinctive bright pink color. The cause of this phenomenon in other hypersaline sites has been attributed to halophiles, Dunaliella, and Salinibacter, however, a systematic analysis of the microbial communities, their functional features, and the prevalence of pigment-producing-metabolisms has not been previously studied. Through metagenomic sequencing and culture-based approaches, our results evidence that Lake Hillier is composed of a diverse set of microorganisms including archaea, bacteria, algae, and viruses. Our data indicate that the microbiome in Lake Hillier is composed of multiple pigment-producer microbes, including Dunaliella, Salinibacter, Halobacillus, Psychroflexus, Halorubrum, many of which are cataloged as polyextremophiles. Additionally, we estimated the diversity of metabolic pathways in the lake and determined that many of these are related to pigment production. We reconstructed complete or partial genomes for 21 discrete bacteria (N = 14) and archaea (N = 7), only 2 of which could be taxonomically annotated to previously observed species. Our findings provide the first metagenomic study to decipher the source of the pink color of Australia's Lake Hillier. The study of this pink hypersaline environment is evidence of a microbial consortium of pigment producers, a repertoire of polyextremophiles, a core microbiome and potentially novel species. [ABSTRACT FROM AUTHOR]

The energy balance approach helps to understand the limits within which the 'predator–prey' relationship can form, but cannot explain the formation of trophic links in natural multispecies systems. A time balance approach to the study of feeding has been developed to complement it. In the hypersaline Lake Moynaki (Crimea) which has a simple food web, there is one omnivorous species, Gammarus aequicauda, and two abundant prey, planktonic Moina salina and benthic Baeotendipes noctivagus. The size of M. salina ranges from 1.0 to 1.2 mm, and the size of B. noctivagus larvae from 9.0 to 10.0 mm. In experiments, elements of time balance were evaluated during feeding of G. aequicauda in the presence of both prey species, i.e., the duration of time spent searching before capture, handling prey, and resting between attempts to eat a chironomid larva. In all experiments, G. aequicauda consumed both kinds of prey. The maximum predation rate of G. aequicauda on the smaller sized M. salina was limited by searching and handling time, but on the larger B. noctivagus it was limited by digestion time. Feeding solely on chironomid larvae may well satisfy the energy needs of G. aequicauda. However, the food ration of G. aequicauda may be 50% higher if it feeds in the presence of both prey species than if feeding only on chironomid larvae. The presence of chironomid larvae more than halved the consumption of M. salina, compared to when cladocerans were the only prey. [ABSTRACT FROM AUTHOR]

The results of lithological and mineralogical studies of the Holocene bottom sediments from the shallow hypersaline (mineralization up to 282 g/L) Bolshoi Bagan Lake, located in the East Baraba Lowland (southwestern Siberia), are presented. The research methods included X-ray diffractometry (XRD), infrared spectroscopy, laser grain size analysis, scanning electron microscopy, elemental composition study, and radiocarbon (14C AMS) dating. It was found that intensive authigenic minerogenesis occurred in the lake basin during the Holocene. Halite, gypsum, and carbonates dominate among the newly formed mineral phases. Mg-calcites with different Mg contents, excess-Ca dolomites, aragonite, and occasionally Mg-siderite have been established in the assemblage of carbonate minerals by the mathematical modeling of complex XRD patterns. The mineralogical and crystallochemical studies, supplemented by the results of other analyses, allowed us to identify four stages of the evolution of Bolshoi Bagan Lake in the Holocene, due to variations in the regional climate. The boundaries of the stages generally correspond to the boundaries of the climatic stratigraphical phases by the Blytt–Sernander classification: stage I (the end of the Boreal), lake formation, humid climate; stage II (Atlantic), climate drying, shallowing of the lake; stage III (Subboreal), unstable climate, frequent change of conditions; stage IV (Sub-Atlantic), moderately cool and dry climate. The mineralogical signals of the global climatic Bond events in southwestern Siberia have been identified. [ABSTRACT FROM AUTHOR]

Simple Summary: The Laguna Negra is a high-altitude hypersaline lake located in the Puna region in Argentina, hosting microbial mats and modern stromatolites, microbially formed rocks found throughout the geological record. Some recent studies have shown the relevance of the lakes in this region for (i) the discovery of new extremophiles, particularly those tolerant to high UV and, furthermore, (ii) the study of biosignatures in stromatolites. In this work, a detailed survey, layer by layer, of the microbial diversity of the most widespread microbial mat in the Laguna Negra was reported, to unravel the spatial arrangement of the microbial community. The results reveal the vertical distribution of the main prokaryotic microbial taxa, and underline abundant Deinococcus-Thermus at the top of the microbial mat with high amounts of deinoxanthin, which may help the total community to cope with high UV radiation. This study allows a better understanding of the community strategies to thrive under environmental stressors in the Laguna Negra and its counterparts in the Altiplano-Puna region. The Altiplano-Puna region is a high-altitude plateau in South America characterized by extreme conditions, including the highest UV incidence on Earth. The Laguna Negra is a hypersaline lake located in the Catamarca Province, northwestern Argentina, where stromatolites and other microbialites are found, and where life is mostly restricted to microbial mats. In this study, a particular microbial mat that covers the shore of the lake was explored, to unravel its layer-by-layer vertical structure in response to the environmental stressors therein. Microbial community composition was assessed by high-throughput 16S rRNA gene sequencing and pigment content analyses, complemented with microscopy tools to characterize its spatial arrangement within the mat. The top layer of the mat has a remarkable UV-tolerance feature, characterized by the presence of Deinococcus-Thermus and deinoxanthin, which might reflect a shielding strategy to cope with high UV radiation. Chloroflexi and Deltaproteobacteria were abundant in the second and third underlying layers, respectively. The bottom layer harbors copious Halanaerobiaeota. Subspherical aggregates composed of calcite, extracellular polymeric substances, abundant diatoms, and other microorganisms were observed all along the mat as the main structural component. This detailed study provides insights into the strategies of microbial communities to thrive under high UV radiation and hypersalinity in high-altitude lakes in the Altiplano-Puna region. [ABSTRACT FROM AUTHOR]

Nitrate-reducing Fe(II)-oxidizing (NRFeOx) microorganisms contribute to nitrogen, carbon, and iron cycling in freshwater and marine ecosystems. However, NRFeOx microorganisms have not been investigated in hypersaline lakes, and their identity, as well as their activity in response to salinity, is unknown. In this study, we combined cultivation-based most probable number (MPN) counts with Illumina MiSeq sequencing to analyze the abundance and community compositions of NRFeOx microorganisms enriched from five lake sediments with different salinities (ranging from 0.67 g/L to 346 g/L). MPN results showed that the abundance of NRFeOx microorganisms significantly (P, 0.05) decreased with increasing lake salinity, from 7.55 - 103 to 8.09 cells/g dry sediment. The community composition of the NRFeOx enrichment cultures obtained from the MPNs differed distinctly among the five lakes and clustered with lake salinity. Two stable enrichment cultures, named FeN-EHL and FeN-CKL, were obtained from microcosm incubations of sediment from freshwater Lake Erhai and hypersaline Lake Chaka. The culture FeN-EHL was dominated by genus Gallionella (68.4%), while the culture FeN-CKL was dominated by genus Marinobacter (71.2%), with the former growing autotrophically and the latter requiring an additional organic substrate (acetate) and Fe(II) oxidation, caused to a large extent by chemodenitrification [reaction of nitrite with Fe(II)]. Short-range ordered Fe(III) (oxyhydr)oxides were the product of Fe(II) oxidation, and the cells were partially attached to or encrusted by the formed iron minerals in both cultures. In summary, different types of interactions between Fe(II) and nitrate-reducing bacteria may exist in freshwater and hypersaline lakes, i.e., autotrophic NRFeOx and chemodenitrification in freshwater and hypersaline environments, respectively. [ABSTRACT FROM AUTHOR]

In 2018–2019, a year-round study of the hypersaline Moynaki Lake, western Crimea, was conducted. In mid-summer 2018, along with Moina salina, which had previously been reported from the lake, the year-round presence of further two cladoceran species, Chydorus sphaericus and Bosmina (Eubosmina) coregoni, was recorded there for the first time. None of those species had ever been registered from hypersaline waters anywhere else. Their introduction seems to have occurred because of a salinity decrease, even though the modern level of salinity has been observed the same level for at least the past 20 years. The presently highly eutrophic environment of Moynaki Lake is probably sufficiently energy-rich to sustain cladoceran osmo-adaptations. [ABSTRACT FROM AUTHOR]

Sambhar Salt Lake, situated in the state of Rajasthan, India is a unique temperate hypersaline ecosystem. Exploration of the salt lake microbiome will enable us to understand microbiome functioning in nutrient-deprived extreme conditions, as well as enrich our understanding of the environment-specific microbiome evolution. The current study has been designed to explore the Sambhar Salt Lake microbiome with a culture-independent multi-omics approach to define its metagenomic features and prevalent metabolic functionaries. The rRNA feature and protein feature-based phylogenetic reconstruction synchronously (R = 0.908) indicated the dominance of the archaea (Euryarchaeota) and bacteria (Firmicutes, Proteobacteria, Bacteroidetes, and Actinobacteria). Metabolic reconstruction identified selective enrichment of the protein features associated with energy harvesting and stress tolerance (osmotic, oxidative, metal/metalloid, heat/cold, antibiotic, and desiccation). Metabolites identified with metabolome analysis confirmed physiological adaptation of the lake microbiome within a hypersaline and nutrient-deprived environment. Comparative metagenomics of the 212 metagenomes representing freshwater, alkaline, and saline ecosystem microbiome indicated the selective enrichment of the microbial groups and genetic features. The current study elucidates microbiome functioning within the nutrient-deprived harsh ecosystems. In summary, the current study harnessing the strength of multi-omics and comparative metagenomics indicates the environment-specific microbiome evolution. [ABSTRACT FROM AUTHOR]

Sambhar Salt Lake, situated in the state of Rajasthan, India is a unique temperate hypersaline ecosystem. Exploration of the salt lake microbiome will enable us to understand microbiome functioning in nutrient-deprived extreme conditions, as well as enrich our understanding of the environment-specific microbiome evolution. The current study has been designed to explore the Sambhar Salt Lake microbiome with a culture-independent multi-omics approach to define its metagenomic features and prevalent metabolic functionaries. The rRNA feature and protein feature-based phylogenetic reconstruction synchronously (R = 0.908) indicated the dominance of the archaea (Euryarchaeota) and bacteria (Firmicutes, Proteobacteria, Bacteroidetes, and Actinobacteria). Metabolic reconstruction identified selective enrichment of the protein features associated with energy harvesting and stress tolerance (osmotic, oxidative, metal/metalloid, heat/cold, antibiotic, and desiccation). Metabolites identified with metabolome analysis confirmed physiological adaptation of the lake microbiome within a hypersaline and nutrient-deprived environment. Comparative metagenomics of the 212 metagenomes representing freshwater, alkaline, and saline ecosystem microbiome indicated the selective enrichment of the microbial groups and genetic features. The current study elucidates microbiome functioning within the nutrient-deprived harsh ecosystems. In summary, the current study harnessing the strength of multi-omics and comparative metagenomics indicates the environment-specific microbiome evolution.

Viruses play vital biogeochemical and ecological roles by (a) expressing auxiliary metabolic genes during infection, (b) enhancing the lateral transfer of host genes, and (c) inducing host mortality. Even in harsh and extreme environments, viruses are major players in carbon and nutrient recycling from organic matter. However, there is much that we do not yet understand about viruses and the processes mediated by them in the extreme environments such as hypersaline habitats. The Great Salt Lake (GSL) in Utah, United States is a hypersaline ecosystem where the biogeochemical role of viruses is poorly understood. This study elucidates the diversity of viruses and describes virus–host interactions in GSL sediments along a salinity gradient. The GSL sediment virosphere consisted of Haloviruses (32.07 ± 19.33%) and members of families Siphoviridae (39.12 ± 19.8%), Myoviridae (13.7 ± 6.6%), and Podoviridae (5.43 ± 0.64%). Our results demonstrate that salinity alongside the concentration of organic carbon and inorganic nutrients (nitrogen and phosphorus) governs the viral, bacteria, and archaeal diversity in this habitat. Computational host predictions for the GSL viruses revealed a wide host range with a dominance of viruses that infect Proteobacteria, Actinobacteria, and Firmicutes. Identification of auxiliary metabolic genes for photosynthesis (psbA), carbon fixation (rbcL, cbbL), formaldehyde assimilation (SHMT), and nitric oxide reduction (NorQ) shed light on the roles played by GSL viruses in biogeochemical cycles of global relevance.

Viruses play vital biogeochemical and ecological roles by (a) expressing auxiliary metabolic genes during infection, (b) enhancing the lateral transfer of host genes, and (c) inducing host mortality. Even in harsh and extreme environments, viruses are major players in carbon and nutrient recycling from organic matter. However, there is much that we do not yet understand about viruses and the processes mediated by them in the extreme environments such as hypersaline habitats. The Great Salt Lake (GSL) in Utah, United States is a hypersaline ecosystem where the biogeochemical role of viruses is poorly understood. This study elucidates the diversity of viruses and describes virus–host interactions in GSL sediments along a salinity gradient. The GSL sediment virosphere consisted of Haloviruses (32.07 ± 19.33%) and members of families Siphoviridae (39.12 ± 19.8%), Myoviridae (13.7 ± 6.6%), and Podoviridae (5.43 ± 0.64%). Our results demonstrate that salinity alongside the concentration of organic carbon and inorganic nutrients (nitrogen and phosphorus) governs the viral, bacteria, and archaeal diversity in this habitat. Computational host predictions for the GSL viruses revealed a wide host range with a dominance of viruses that infect Proteobacteria , Actinobacteria , and Firmicutes. Identification of auxiliary metabolic genes for photosynthesis (psbA), carbon fixation (rbc L, cbb L), formaldehyde assimilation (SHMT), and nitric oxide reduction (Nor Q) shed light on the roles played by GSL viruses in biogeochemical cycles of global relevance. [ABSTRACT FROM AUTHOR]

Cladophora spp. constantly or periodically form floating and benthic mats in Crimean hypersaline lakes and lagoons. In 2017–2018, characteristics of the Cladophora mats and the microalgae on Cladophora filaments were studied employing field research and microscopy. The whole Cladophora mat has a vertical structure, including the upper and lower layers of the floating mat and benthic mat. In total, 50 species of microalgae were found: 40 of them belonged to Bacillariophyta (Bacillariophyceae and Mediophyceae), two to Haptophyta (Coccolithophyceae), four to Miozoa (Dinophyceae), one to Chlorophyta (Zygnematophyceae) and three to Cyanobacteria (Cyanophyceae). Floating layers of the mat differed significantly in species composition from the benthic mat. The total abundance of microalgae and their biomass on Cladophora (per unit area of filaments) varied widely within sampling sites from 3.79 × 106 to 5.04 × 108 cells m–2 and 2.6 to 2197.8 mg m–2. The total mass of microalgae achieved more than 32% of the mass of Cladophora, averaging 7.7% (standard deviation = 13.3). [ABSTRACT FROM AUTHOR]

Abstract Lacustrine stromatolites were widespread in the Miocene Wudaoliang Group (stromatolites of the Wudaoliang Group), northern Tibetan Plateau; but only at one location nearby the Wudaoliang Town, they occurred intensively in thick, laterally traceable beds (Wudaoliang stromatolites). Although deposited in lacustrine environment, the lack of fossils in these rocks hampers determining whether the stromatolites formed in freshwater or saline conditions. To address this problem, and in an attempt to identify criteria to distinguish differences of freshwater and saline conditions, we studied the laminae microfabrics, stable carbon and oxygen isotope ratios, rare earth element patterns and biomarkers of the stromatolites. These stromatolites can be divided into fenestral stromatolites and agglutinated stromatolites. The fabric of fenestral stromatolites is formed by microcrystalline carbonate enclosing spar-cemented, angular crystal traces. Essentially, this fabric is interpreted as pseudomorph after former formed evaporite crystals. Faecal pellets identical to that of the present-day brine shrimp Artemia, lack of other eukaryotic fossils, and stable isotopic signals point to a shallow, evaporation-dominated hypersaline lake setting. Covariation of carbon and oxygen isotopes indicates hydrologically closed conditions of the Miocene lake on northern Tibetan Plateau. However, if compared to other lacustrine carbonates of the Wudaoliang Group, the high δ13C values of the investigated Wudaoliang stromatolites reveal an additional photosynthetic effect during the deposition of the stromatolites. Furthermore, although no direct evidence is available from field observations and microfabrics, a positive europium anomaly of Wudaoliang stromatolites indicates that a palaeo-hydrothermal inflow system had existed in the outcrop area. These new results favour a hypersaline lake setting subject to hot spring inflow for the Wudaoliang stromatolites, in contrast to earlier interpretations suggesting a freshwater lake setting (e.g. Yi et al., Journal of Mineralogy and Petrology 28: 106–113, 2008; Zeng et al., Journal of Mineralogy and Petrology 31: 111–119, 2011). This approach may be appropriate for other lacustrine, unfossiliferous microbialites in settings where the environmental conditions are difficult to determine.

The ecosystems of hypersaline waters are characterized by the simplified trophic webs with the 'loss' of predators. In the absence of predators, their role can be effectively performed by omnivorous as Gammaridae species. In Lake Moynaki, a small hypersaline lake, Gammarus aequicauda is one of the most abundant animal species along with chironomid larvae Baeotendipes noctivagus. Both these species are promising objects to use in polyaquaculture, and this adds an importance to know their trophic relations. To analyse G. aequicauda feeding on B. noctivagus, the field and experimental studies were conducted in 2018 and 2019. In two habitats (Ruppia thickets and free water), the abundance of both species significantly differed, and in the thickets of Ruppia, the Gammarus abundance was higher, and of chironomid larvae was less. Taking into account our experimental results and chironomid larvae abundance in the lake during the study period (from 460 to 3,200 ind./m2), the authors conclude that larvae abundance did not limit the rate of their consumption in the lake by G. aequicauda, and one can consume up to 4 larvae per day. Thus, G. aequicauda could receive a diet of about 45% of their weight consuming about 2% of the available larvae daily in areas without the marine grass Ruppia thickets. In Ruppia thickets, chironomid larvae are not important food of G. aequicauda because the Ruppia leaves play a more important role in gammarid diet. With sufficient plant food resources, G. aequicauda can be successfully cultivated together with chironomid larvae. [ABSTRACT FROM AUTHOR]

The Altiplano-Puna region is a high-altitude plateau in South America characterized by extreme conditions, including the highest UV incidence on Earth. The Laguna Negra is a hypersaline lake located in the Catamarca Province, northwestern Argentina, where stromatolites and other microbialites are found, and where life is mostly restricted to microbial mats. In this study, a particular microbial mat that covers the shore of the lake was explored, to unravel its layer-by-layer vertical structure in response to the environmental stressors therein. Microbial community composition was assessed by high-throughput 16S rRNA gene sequencing and pigment content analyses, complemented with microscopy tools to characterize its spatial arrangement within the mat. The top layer of the mat has a remarkable UV-tolerance feature, characterized by the presence of Deinococcus-Thermus and deinoxanthin, which might reflect a shielding strategy to cope with high UV radiation. Chloroflexi and Deltaproteobacteria were abundant in the second and third underlying layers, respectively. The bottom layer harbors copious Halanaerobiaeota. Subspherical aggregates composed of calcite, extracellular polymeric substances, abundant diatoms, and other microorganisms were observed all along the mat as the main structural component. This detailed study provides insights into the strategies of microbial communities to thrive under high UV radiation and hypersalinity in high-altitude lakes in the Altiplano-Puna region.

Desulfohalobium retbaense (Ollivier et al. 1991) is the type species of the polyphyletic genus Desulfohalobium, which comprises, at the time of writing, two species and represents the family Desulfohalobiaceae within the Deltaproteobacteria. D. retbaense is a moderately halophilic sulfate-reducing bacterium, which can utilize H(2) and a limited range of organic substrates, which are incompletely oxidized to acetate and CO(2), for growth. The type strain HR(100) (T) was isolated from sediments of the hypersaline Retba Lake in Senegal. Here we describe the features of this organism, together with the complete genome sequence and annotation. This is the first completed genome sequence of a member of the family Desulfohalobiaceae. The 2,909,567 bp genome (one chromosome and a 45,263 bp plasmid) with its 2,552 protein-coding and 57 RNA genes is a part of the Genomic Encyclopedia of Bacteria and Archaea project.

Inland athalassohaline solar salterns provide unique opportunity to study microbial successions along salinity gradients that resemble transition in natural hypersaline lakes. We analyzed for the first time 16S rRNA gene amplicon sequences of bacteria (V1–V2) and archaea (V4–V5) in saltern brines of India's largest inland hypersaline Sambhar Lake. Brines of the salterns (S1–S4) are alkaline (pH 9.5–10.5) with salinities of 130, 170, 280 and 350 gL−1 respectively. 16S rRNA gene copy-number of archaea outnumbered that of bacteria in all salterns. Their diversity also increased along S1 through S4, while that of bacteria decreased. Brines of S3 and S4 were dominated by specialized extreme halophilic bacterial (Halanaerobiales, Rhodothermaceae) and archaeal (Halobacteriales, Haloferacales) members with recognized salt-in strategy for osmoadaptation. Microbial assemblages positively correlated to saltern pH, total salinity, and ionic composition. Archaea in S1 and S2 were unprecedentedly represented by poorly known as-yet uncultivated groups, Woesearchaeota (90.35–93.51%) and Nanohaloarchaeota that belong to the newly proposed nano-sized superphylum DPANN. In fact, these taxa were identified in archaeal datasets of other athalassohaline salterns after re-analysis using latest RDP database. Thus, microbial compositions in hypersaline lakes are complex and need revisit particularly for their archaeal diversity to understand their hitherto unknown ecological function in extreme environments. [ABSTRACT FROM AUTHOR]

Gammarus aequicauda (Amphipoda) and Moina salina (Cladocera) are dominant species and promising objects for aquaculture in hypersaline lakes. In the Crimean hypersaline lake Moynaki, population dynamics of their abundance was studied and experiments on feeding were also done. In 2018 and 2019, the average concentrations of G. aequicauda and M. salina differed between the thickets of sea grass Ruppia and the areas without Ruppia. The concentration of G. aequicauda in the thickets was on average from 52 to 126 times higher than in the Ruppia‐free areas. Moina demonstrated the opposite trend. There was a significant negative correlation between the abundances of these species in the Ruppia thickets (R = −0.746, p =.005). The experimental results on trophic relation showed that the amount of Moina eaten by one G. aequicauda varied from 0.04 to 9.80 ind./hr and depended on the average Moina concentration. Calculation showed that the gammarid population consumed about 1.0%–1.5% of available preys per day. Gammarids were able to graze up to 60%–65% of the Moina population in 10 days. To develop integrated multi‐trophic aquaculture in saline/hypersaline waters, character of 'gammarus–moina' trophic relation and the biological peculiarities of these species must be taken into account. [ABSTRACT FROM AUTHOR]

Saline lakes are subject to numerous environmental impacts related to human activities, changing the chemical and biological natural conditions of the ecosystem. Sustainable development depends on the conservation of such delicate saline ecosystems, which may hold distinctive biodiversity. Pollution is one of the major threats to surface water bodies, for example by increasing nutrient contents and organic pollutants, including endocrine disrupting chemicals. Microbially mediated redox processes exert a fundamental control on nutrient turnover and contaminant removal. This study examines the influence of land use on the distribution of endocrine disrupting chemicals as well as on the microbial community composition in lacustrine sediments from Pétrola saline Lake (SE Spain). The lake is impacted by anthropogenic activities (agriculture, farming, mining and urban wastewater spills). Applying chemical and molecular tools (sequencing of 16S rRNA gene) showed a clear influence of land use on the chemistry and bacterial abundance of the lake sediments. The sampling points closer to wastewater outflows and mining ponds (2635, 2643 and 2650) showed fewer numbers and types of endocrine disrupting chemicals as well as a smaller number of families in the microbial community. These findings improve our understanding of how land use affects both water chemistry and the abundance of organisms responsible for biogeochemical cycles. [ABSTRACT FROM AUTHOR]

The large use of conventional plastics has resulted in serious environmental problems. Polyhydroxyalkanoates represent a potent replacement to synthetic plastics because of their biodegradable nature. This study aimed to screen bacteria and archaea isolated from an extreme environment, the salt lake Chott El Jerid for the accumulation of these inclusions. Among them, two archaeal strains showed positive results with phenotypic and genotypic methods. Phylogenetic analysis, based on the 16S rRNA gene, indicated that polyhydroxyalkanoate (PHA)-producing archaeal isolates CEJGTEA101 and CEJEA36 were related to Natrinema altunense and Haloterrigena jeotgali, respectively. Gas chromatography and UV-visible spectrophotometric analyses revealed that the PHA were identified as polyhydroxybutyrate and polyhydroxyvalerate, respectively. According to gas chromatography analysis, the strain CEJGTEA101 produced maximum yield of 7 wt % at 37 °C; pH 6.5; 20% NaCl and the strain CEJEA36 produced 3.6 wt % at 37 °C; pH 7; 25% NaCl in a medium supplemented with 2% glucose. Under nutritionally optimal cultivation conditions, polymers were extracted from these strains and were determined by gravimetric analysis yielding PHA production of 35% and 25% of cell dry weight. In conclusion, optimization of PHA production from inexpensive industrial wastes and carbon sources has considerable interest for reducing costs and obtaining high yield. [ABSTRACT FROM AUTHOR]

Questions: What are the plant communities and vegetation pattern on shorelines of a hypersaline desiccating lake and which environmental factors influence the zonation pattern of these communities? How is the species richness along salt and moisture gradients? Which plant communities and rare species are threatened by the impact of lake shrinkage? Which advice can be offered for the management and restoration of the area? Study area: Lake Urmia, NW Iran, one of the world's largest saltwater lakes. Methods: We established 14 transects with 174 relevés in different parts of the lake and collected soil samples. TWINSPAN was used for vegetation classification and NMDS for ordination. Results: We distinguished 27 plant communities and described as new the associations Salicornio iranicae-Bolboschoenetum affinis, Tamaricetum octandrae, Salicornietum iranicae, Climacopteretum crassae, Suaedo altissimae-Climacopteretum crassae and the Atriplici leucocladae-Caroxyletum dendroidis. We present an overview of the syntaxa and illustrate typical zonation patterns of the lake's salt marsh vegetation under current conditions of desiccation. Conclusions: The vegetation pattern and vegetation dynamics of the area is seriously affected by the hydrological changes around Lake Urmia. Fragmentation of wetland plant communities due to water shortage, increasing disturbance and invasion of ruderal species affect the floristic composition of the lakeside. Increasing soil salinity and decreasing moisture lead to area loss or even disappearance of certain plant communities. Plant communities with C4 annuals or pioneer ruderal species are developing or spreading in sites with low soil salinity or on sandy soils. We strongly recommend vegetation monitoring using permanent plots to improve the predictability of succession trends. Groundwater exploitation, unsustainable use of water resources in the catchment area, any further disturbance in the lakeside area including grazing and artificial plantation activities need to be prohibited. [ABSTRACT FROM AUTHOR]

The sedimentary record of the Dead Sea provides an exceptional high-resolution archive of past climate changes in the drought-sensitive eastern Mediterranean-Levant, a key region for the development of humankind at the boundary of global climate belts. Moreover, it is the only deep hypersaline lake known to have deposited long sequences of finely laminated, annually deposited sediments (i.e. varves) of varied compositions, including aragonite, gypsum, halite and clastic sediments. Vast efforts have been made over the years to decipher the environmental information stored in these evaporitic-clastic sequences spanning from the Pleistocene Lake Amora to the Holocene Dead Sea. A general characterisation of sediment facies has been derived from exposed sediment sections, as well as from shallow- and deep-water sediment cores. During high lake stands and episodes of positive water budget, mostly during glacial times, alternating aragonite and detritus laminae ('aad' facies) were accumulated, whereas during low lake stands and droughts, prevailing during interglacials, laminated detritus ('ld' facies) and laminated halite ('lh' facies) dominate the sequence. In this paper, we (i) review the three types of laminated sediments of the Dead Sea sedimentary record ('aad', 'ld' and 'lh' facies), (ii) discuss their modes of formation, deposition and accumulation, and their interpretation as varves, and (iii) illustrate how Dead Sea varves are utilized for palaeoclimate reconstructions and for establishing floating chronologies. Image 1 • The Dead Sea is the only deep hypersaline lake with varved sediments. • The chronological and paleoclimatic value of Dead Sea varves is demonstrated. • The interpretation of alternating aragonite-detritus laminae as varves is evaluated. • Lake monitoring confirms the interpretation of laminated halite as varves. • Distinguishing between annual and non-annual laminations requires micro-facies analyses. [ABSTRACT FROM AUTHOR]

Abstract The sediment–water transition zone in an aquatic system is key role to the distribution of contaminants between the surface water and sediment pore water. Maharlu Lake is a seasonal hypersaline lake in the central part of the Maharlu Basin in Southern Iran. Wastewater of various types produced within the basin is released into the seasonal freshwater rivers that ultimately drain into the lake. Samples were collected through one complete period of the lake water-level fluctuation. Lake surface water and shallow sediment pore water samples were collected three times at three piezometric stations at different distances from the river inflow points. Lake sediment samples were collected twice, and water samples from the inflowing rivers were collected five times. Changes in surface runoff and agricultural wastewater inflows were responsible for seasonal hydrochemical changes and changes in the As concentrations in the inflowing rivers. Data from the stations close to the river inflows indicated that the dissolved As concentrations across the sediment–water interface in Maharlu Lake are mostly controlled by evaporation and interactions between the surface water and shallow pore water. However, data from the station far from the freshwater inflows indicated that the brine and precipitated evaporites were at equilibrium and redox processes (e.g., iron (hydr)oxide dissolution and secondary sulphide precipitation) control the dissolved As concentration in pore water. The results confirmed the role of lake water evaporation in As enrichment and As sequestration by secondary sulphide minerals in sediment below the sediment–water interface. Climate change may alter the lake chemistry and As behavior in near future. Highlights • Measured total arsenic concentration in inflow rivers water, surface/pore water and shallow sediment in playa salt lake. • Investigate the distribution of arsenic across the sediment-water interface. • Hydrological processes controls dissolved arsenic concentration at area of lake near to the inflowing rivers. • Redox reactions controls dissolved arsenic concentration at area of lake far away from the inflowing rivers. • As in inflow rivers and surface/pore wtar of lake changes seasonally and inter-annually. [ABSTRACT FROM AUTHOR]

Saline lakes are subject to numerous environmental impacts related to human activities, changing the chemical and biological natural conditions of the ecosystem. Sustainable development depends on the conservation of such delicate saline ecosystems, which may hold distinctive biodiversity. Pollution is one of the major threats to surface water bodies, for example by increasing nutrient contents and organic pollutants, including endocrine disrupting chemicals. Microbially mediated redox processes exert a fundamental control on nutrient turnover and contaminant removal. This study examines the influence of land use on the distribution of endocrine disrupting chemicals as well as on the microbial community composition in lacustrine sediments from Pétrola saline Lake (SE Spain). The lake is impacted by anthropogenic activities (agriculture, farming, mining and urban wastewater spills). Applying chemical and molecular tools (sequencing of 16S rRNA gene) showed a clear influence of land use on the chemistry and bacterial abundance of the lake sediments. The sampling points closer to wastewater outflows and mining ponds (2635, 2643 and 2650) showed fewer numbers and types of endocrine disrupting chemicals as well as a smaller number of families in the microbial community. These findings improve our understanding of how land use affects both water chemistry and the abundance of organisms responsible for biogeochemical cycles.

The large use of conventional plastics has resulted in serious environmental problems. Polyhydroxyalkanoates represent a potent replacement to synthetic plastics because of their biodegradable nature. This study aimed to screen bacteria and archaea isolated from an extreme environment, the salt lake Chott El Jerid for the accumulation of these inclusions. Among them, two archaeal strains showed positive results with phenotypic and genotypic methods. Phylogenetic analysis, based on the 16S rRNA gene, indicated that polyhydroxyalkanoate (PHA)-producing archaeal isolates CEJGTEA101 and CEJEA36 were related to Natrinema altunense and Haloterrigena jeotgali, respectively. Gas chromatography and UV-visible spectrophotometric analyses revealed that the PHA were identified as polyhydroxybutyrate and polyhydroxyvalerate, respectively. According to gas chromatography analysis, the strain CEJGTEA101 produced maximum yield of 7 wt % at 37 °C; pH 6.5; 20% NaCl and the strain CEJEA36 produced 3.6 wt % at 37 °C; pH 7; 25% NaCl in a medium supplemented with 2% glucose. Under nutritionally optimal cultivation conditions, polymers were extracted from these strains and were determined by gravimetric analysis yielding PHA production of 35% and 25% of cell dry weight. In conclusion, optimization of PHA production from inexpensive industrial wastes and carbon sources has considerable interest for reducing costs and obtaining high yield.