Hypersaline Environments Research Articles

Enhancement of stress resistance of electroactive biofilms against hypersaline shock via exogenous electron mediator addition

Unexpected hypersaline shock from saline wastewater poses a common challenge in the biological treatment processes of WWPTs. Bioelectrochemical systems (BESs) possess an inherent advantage for treating hypersaline wastewater. The elevated salinity enhances the wastewater’s conductivity, which in turn significantly accelerates the electron and proton transfer within the system. However, excessive increases in salinity can impede electron transport capacity, potentially resulting in cell plasmolysis and system failure in severe instances. Here, we investigated the impact of electron mediator (EM) addition on the resilience of electroactive biofilms (EB) to hypersaline environments in BESs. The EB developed under anthraquinone-2,6-disulphonic disodium salt (AQDS) addition obtained preferable electrochemical properties (e.g., current output, redox peak current, conductivity, electron transfer capacity) under hypersaline shock and showed superior recovery post-hypersaline stress. Partial least squares path modeling (PLS-PM) analysis indicated that the enhanced secretion of extracellular polymeric substances (EPS) and the elevated ratio of proteins to polysaccharides are likely pivotal in the formation of EB with high electrochemical activity. Meanwhile, AQDS addition constructed more complex microbial network and enriched halotolerant bacteria (e.g., Solibacillus). Higher mean function abundance of replication & repair, stress tolerance, and biofilm formation were achieved by EM addition. The results of this study present a promising approach to augment the pressure tolerance of EBs, thereby broadening the practical applications of BESs.

Cambrian-Ordovician trace fossils of the Basissletta region, northeast Spitsbergen, Svalbard

Trace fossils of the Cambrian–Ordovician sedimentary succession of the Basissletta region, northeast Spitsbergen, Svalbard, belong to three ichnoassemblages. The first one, composed of Monocraterion and Diplocraterion, belongs to the Skolithos ichnofacies and characterises sandstones of the Tokammane Formation (lower Cambrian: Terreneuvian) deposited in a shallow subtidal setting. The overlying carbonates with pseudomorphs after evaporites (uppermost part of Terreneuvian and the Cambrian Series 2) display abundant Balanoglossites. These beds were deposited in an oxygenated but hypersaline environment. The younger Ordovician carbonates of the Kirtonryggen Formation and the mixed carbonate-clastic deposits of the Valhallfonna Formation display a more diverse but poorly preserved trace fossil suite (Phycodes, Curvolithus, Planolites, Palaeophycus) typical of the archetypal Cruziana ichnofacies. Some parts of the succession are not bioturbated, and these are characterised by dark coloured fine-grained sediments with primary lamination. They were mostly deposited between the normal and storm wave base or below the storm wave base in oxic to anoxic environments.

Hyperostosis in Fishes: An Update With New Species Records.

Literature reports of hyperostosis are often misleading and have been confused with osteomas, a pathological condition. Hyperostotic bones are known to occur only in bony fishes of the class Actinopterygii, within at least 16 orders, 35 families, 89 genera, and 153 species. They are present almost exclusively in marine fishes and exceptionally in a few extinct freshwater species known from hypersaline environments and one extant cichlid. Hyperostosis is best represented in the family Carangidae where it is known to occur in 53 of approximately 181 valid species. We also provide a synthetic report on what we know and what misconceptions exist regarding hyperostosis. Patterns of hyperostosis are often species-specific but provide no useful phylogenetic information. In species known to develop hyperostosis, it is usually not apparent (non-histologically) in juveniles and typically only becomes fully developed in the largest individuals. The timing of hyperostosis on-set in different bones is often sequential rather than simultaneous across different bones. Most marine Neoteleostei have acellular skeletons but histological observations have shown that in species exhibiting hyperostosis, areas of active remodeling are composed primarily of cellular bone characterized by a rich vascular network and bone-resorbing osteoclasts.

The Fungal Side of the Story: Saprotrophic- vs. Symbiotrophic-Predicted Ecological Roles of Fungal Communities in Two Meromictic Hypersaline Lakes from Romania

Over three-quarters of Earth’s surface exhibits extreme environments where life thrives under harsh physicochemical conditions. While prokaryotes have often been investigated in these environments, only recent studies have revealed the remarkable adaptability of eukaryotes, in particular fungi. This study explored the mycobiota of two meromictic hypersaline lakes, Ursu and Fără Fund, in Transylvania (Romania). The intrinsic and extrinsic fungal diversity was assessed using amplicon sequencing of environmental DNA samples from sediments, water columns, surrounding soils, and an associated rivulet. The fungal communities, illustrated by the 18S rRNA gene and ITS2 region, exhibited contrasting patterns between the lakes. The ITS2 region assessed better than the 18S rRNA gene the fungal diversity. The ITS2 data showed that Ascomycota was the most abundant fungal group identified in both lakes, followed by Aphelidiomycota, Chytridiomycota, and Basidiomycota. Despite similar α-diversity levels, significant differences in fungal community structure were observed between the lakes, correlated with salinity, total organic carbon, total nitrogen, and ammonium. Taxonomic profiling revealed depth-specific variations, with Saccharomycetes prevalent in Ursu Lake’s deeper layers and Lecanoromycetes prevalent in the Fără Fund Lake. The functional annotation using FungalTraits revealed diverse ecological roles within the fungal communities. Lichenized fungi were dominant in Fără Fund Lake, while saprotrophs were abundant in Ursu Lake. Additionally, wood and soil saprotrophs, along with plant pathogens, were more prevalent in the surrounding soils, rivulet, and surface water layers. A global overview of the trophic relations in each studied niche was impossible to establish due to the unconnected graphs corresponding to the trophic interactions of the analyzed fungi. Plotting the unweighted connected subgraphs at the genus level suggests that salinity made the studied niches similar for the identified taxa. This study shed light on the understudied fungal diversity, distribution, and ecological functions in hypersaline environments.

Interannual differences vs small-scale spatiotemporal variability of spring zooplankton in the Crimean marine hypersaline lake

Ecosystems in the shallow marine hypersaline environment, such as marine lakes, are among the most changeable and have significantly lower species richness than freshwater and marine. It could be assumed that the intricate interconnections in hypersaline water ecosystems are easier to understand than in other aquatic ecosystems. Interannual differences vs small-scale spatiotemporal variabilities were studied in the spring zooplankton of hypersaline Lake Moynaki from 2019 to 2023. Salinity, water temperature, wind speed and direction were measured along with zooplankton sampling. The average spring wind speed and water temperature varied significantly from year to year, seemingly with a certain cyclicity. In total, 17 species were noted in zooplankton. The copepods Acanthocyclops vernalis and Arctodiaptomus salinus were not previously recorded in the lake. Bottom species were found in the plankton, among which the oligochaete Nais pseudobtusa, the gastropod Bittium reticulatum, and dragonfly larvae Gomphus sp. had not previously been found in the lake. Only four species, Gammarus aequicauda, Eucypris mareotica, Moina salina, and Cletocamptus retrogressus were regularly observed en masse. On average, the total zooplankton abundance near the windward shore was 2 times higher than that near the leeward shore and the abundance of individual species was from 2 to 5 times higher. If the values near only one coast were used, then the range of interannual differences would be underestimated or overestimated by approximately 2–4 times. Based on the zooplankton similarity in different years, all years except 2019, are grouped into a single cluster. Various changes are occurring in the lake, which are difficult to present as a complete picture of the cause-and-effect relationships that determine them.

Genome-Scale Metabolic Modeling of Halomonas elongata 153B Explains Polyhydroxyalkanoate and Ectoine Biosynthesis in Hypersaline Environments.

Halomonas elongata thrives in hypersaline environments producing polyhydroxyalkanoates (PHAs) and osmoprotectants such as ectoine. Despite its biotechnological importance, several aspects of the dynamics of its metabolism remain elusive. Here, we construct and validate a genome-scale metabolic network model for H. elongata 153B. Then, we investigate the flux distribution dynamics during optimal growth, ectoine, and PHA biosynthesis using statistical methods, and a pipeline based on shadow prices. Lastly, we use optimization algorithms to uncover novel engineering targets to increase PHA production. The resulting model (iEB1239) includes 1534 metabolites, 2314 reactions, and 1239 genes. iEB1239 can reproduce growth on several carbon sources and predict growth on previously unreported ones. It also reproduces biochemical phenotypes related to Oad and Ppc gene functions in ectoine biosynthesis. A flux distribution analysis during optimal ectoine and PHA biosynthesis shows decreased energy production through oxidative phosphorylation. Furthermore, our analysis unveils a diverse spectrum of metabolic alterations that extend beyond mere flux changes to encompass heightened precursor production for ectoine and PHA synthesis. Crucially, these findings capture other metabolic changes linked to adaptation in hypersaline environments. Bottlenecks in the glycolysis and fatty acid metabolism pathways are identified, in addition to PhaC, which has been shown to increase PHA production when overexpressed. Overall, our pipeline demonstrates the potential of genome-scale metabolic models in combination with statistical approaches to obtain insights into the metabolism of H. elongata. Our platform can be exploited for researching environmental adaptation, and for designing and optimizing metabolic engineering strategies for bioproduct synthesis.

A new type of submarine chimneys built of halite

In contrast to the subaquatic sulphide and carbonate chimneys, which are known from Mid Ocean Ridges and abyssal submarine volcanoes, chimneys built of salts have not been described yet. Here we present such halite chimneys as a new form of cold-water smokers in hypersaline environments. The here described structures rise up from the bottom of the Dead Sea and result from the submarine discharge of saturated halite-dissolution brines into the salt lake, which is at halite saturation and holds remarkable chloride excess. At the interface with the lake brine, halite precipitates instantaneously, forming chimneys up to several meters in height. The brines leading to the formation of these chimneys vary in composition, while their generation processes are similar. Fresh groundwater from surrounding aquifers enters the saline lake sediments and considerably leaches halite in the adjacencies of the lake. Simultaneously, it mixes with ancient brines before it emerges from the lake floor. The distinct differences in composition between the Dead Sea and the emerging chimney brines lead to the instantaneous crystallisation of halite and few other mineral phases. The chimney structure result from the buoyancy flow of the chimney brines, which are less dense then the ambient Dead Sea.The chimneys indicate intense cavitation of massive halite bodies in the subsurface of the Dead Sea environment, a process that leads to increasing formation of hazardous sinkholes. Since chimneys are proven in shallow water but may be expected in deeper parts too, they are comfortably mappable by echo-sounding or aerial imaging. They thus provide in the Dead Sea as in any likewise setting a potent predictive tool to locate dangerous subsurface cavitation and hence areas that are at risk of collapse in the near future.

Metataxonomy and pigments analyses unravel microbial diversity and the relevance of retinal-based photoheterotrophy at different salinities in the Odiel Salterns (SW, Spain)

Salinity has a strong influence on microorganisms distribution patterns and consequently on the relevance of photoheterotrophic metabolism, which since the discovery of proteorhodopsins is considered the main contributor to solar energy capture on the surface of the oceans. Solar salterns constitute an exceptional system for the simultaneous study of several salt concentrations, ranging from seawater, the most abundant environment on Earth, to saturated brine, one of the most extreme, which has been scarcely studied. In this study, pigment composition across the salinity gradient has been analyzed by spectrophotometry and RP-HPLC, and the influence of salinity on microbial diversity of the three domains of life has been evaluated by a metataxonomic study targeting hypervariable regions of 16S and 18S rRNA genes. Furthermore, based on the chlorophyll and retinal content, we have estimated the relative abundance of rhodopsins and photosynthetic reaction centers, concluding that there is a strong correlation between the retinal/chlorophyll a ratio and salinity. Retinal-based photoheterotrophy is particularly important for prokaryotic survival in hypersaline environments, surpassing the sunlight energy captured by photosynthesis, and being more relevant as salinity increases. This has implications for understanding the survival of microorganisms in extreme conditions and the energy dynamics in solar salter ponds.

Unique Features of Extremely Halophilic Microbiota Inhabiting Solar Saltworks Fields of Vietnam.

The artificial solar saltworks fields of Hon Khoi are important industrial and biodiversity resources in southern Vietnam. Most hypersaline environments in this area are characterized by saturated salinity, nearly neutral pH, intense ultraviolet radiation, elevated temperatures and fast desiccation processes. However, the extremely halophilic prokaryotic communities associated with these stressful environments remain uninvestigated. To fill this gap, a metabarcoding approach was conducted to characterize these communities by comparing them with solar salterns in northern Vietnam as well as with the Italian salterns of Motya and Trapani. Sequencing analyses revealed that the multiple reuses of crystallization ponds apparently create significant perturbations and structural instability in prokaryotic consortia. However, some interesting features were noticed when we examined the diversity of ultra-small prokaryotes belonging to Patescibacteria and DPANN Archaea. Surprisingly, we found at least five deeply branched clades, two from Patescibacteria and three from DPANN Archaea, which seem to be quite specific to the Hon Khoi saltworks field ecosystem and can be considered as a part of biogeographical connotation. Further studies are needed to characterize these uncultivated taxa, to isolate and cultivate them, which will allow us to elucidate their ecological role in these hypersaline habitats and to explore their biotechnological and biomedical potential.

O short-branch Microsporidia, where art thou? Identifying diversity hotspots for future sampling

Short-branch Microsporidia were previously shown to form a basal grade within the expanded Microsporidia clade and to branch near the classical, long-branch Microsporidia. Although they share simpler versions of some morphological characteristics, they do not show accelerated evolutionary rates, making them ideal candidates to study the evolutionary trajectories that have led to long-branch microsporidian unique characteristics. However, most sequences assigned to the short-branch Microsporidia are undescribed, novel environmental lineages for which the identification requires knowledge of where they can be found. To direct future isolation, we used the EukBank database of the global UniEuk initiative that contains the majority of the publicly available environmental V4 SSU rRNA gene sequences of protists. The curated OTU table and corresponding metadata were used to evaluate the occurrence of short-branch Microsporidia across freshwater, hypersaline, marine benthic, marine pelagic, and terrestrial environments. Presence–absence analyses infer that short-branch Microsporidia are most abundant in freshwater and terrestrial environments, and alpha- and beta-diversity measures indicate that focusing our sampling effort on these two environments would cover a large part of their overall diversity. These results can be used to coordinate future isolation and sampling campaigns to better understand the enigmatic evolution of microsporidians’ unique characteristics.

Inoculation of halotolerant plant-growth-promoting bacteria improved the growth of chia (Salvia hispanica L.) in saline and nonsaline soils

Context Chia (Salvia hispanica L.), a nutrient-rich crop with potential application in different industries, is sensitive to salinity. Halotolerant plant-growth promoting bacteria could be a biotechnological strategy to increase chia’s salinity tolerance. Aims The aim of this study was to determine the morphological and physiological response of chia plants inoculated with free-living halotolerant plant-growth promoting bacteria and grown in saline soils under greenhouse conditions. Methods A total of 15 bacterial treatments were inoculated to plants potted in soils with three electrical conductivity levels: 0.5, 4, and 6 dS m−1. Mortality and morphological and physiological parameters were evaluated. The measured variables were used to calculate a relative growth index. Key results Bacterial inoculation had a positive effect on plants at 4 dS m−1. Plants inoculated with Pseudomonas sp. AN23, Kushneria sp. T3.7, and C6 (Halomonas sp. 3R12 + Micrococcus luteus SA211) exhibited the best morphological and physiological performance (51% longer shoots, up to 90% heavier roots and up to 400% higher photosynthetic rate than control plants). Moreover, plants inoculated with Kushneria sp. T3.7 and C5 (Halomonas sp. 3R12 + Pseudomonas sp. AN23) showed significant increase in stomatal conductance and transpiration rate (up to 12 times) and in proline production (up to 345 μg g−1 leaf fresh weight) with respect to control plants (8 μg g−1 leaf fresh weight) under saline conditions. Conclusions The analysed extremophilic plant-growth promoting bacteria enhanced growth and stress tolerance in chia, a salt-sensitive crop. Implications Free-living plant-growth promoting bacteria isolated from hypersaline environments have potential for bioinoculant formulation for salinity-sensitive crops.

Characterization of Skoliomonas gen. nov., a haloalkaliphilic anaerobe related to barthelonids (Metamonada).

Metamonads are a large and exclusively anaerobic group of protists. Additionally, they are one of the three clades proposed to ancestrally possess an "excavate" cell morphology, with a conspicuous ventral groove accompanied by a posterior flagellum with a vane. Here, we cultivate and characterize four anaerobic bacterivorous flagellates from hypersaline and alkaline soda lake environments, which represent a novel clade. Small subunit ribosomal RNA (SSU rRNA) gene phylogenies support recent phylogenomic analyses in placing them as the sister of barthelonids, a group that is itself sister to or deeply branching within Fornicata (Metamonada). The new isolates have a distinctive morphology: the hunchbacked cell body is traversed by a narrow ventral groove ending in a large opening to a conspicuous recurrent cytopharynx. The right margin of the groove is defined by a thin "lip." The posterior flagellum bears a wide ventral-facing vane. The narrow ventral groove and elongate cytopharynx are shared with barthelonids. We describe one isolate as Skoliomonas litria, gen. et sp. nov. Further investigation of their mitochondrial-related organelles (MROs) and detailed ultrastructural studies would be important to understanding the adaptation to anaerobic conditions in Metamonads-especially fornicates-as well as the evolution of the "excavate" cell architecture.

Source and variation of the amazing live Sea-Monkey microbiome.

An embryonic diapause in unfavourable conditions has allowed brine shrimp to thrive in hypersaline environments and, unexpectedly, mail-order sachets and small, novelty tanks. Marketed as Sea-Monkeys®, each kit involves a 3-step process to generate adult Artemia within a matter of weeks. Whether these kits also allow for the maintenance of a host-associated microbiome is unclear. Therefore, comparing five replicate tanks under the same culture conditions, we sequenced the 16S ribosomal small subunit (SSU) gene to analyse bacterial community compositions in adults, their surrounding tank water, and their feed. Adult Sea-Monkeys® harboured a bacterial microbiome that was clearly distinguishable from the tank water and food. Furthermore, individual tanks had a notable effect on fine-scale microbiome variation. Several Sea-Monkey bacterial variants appeared absent in environmental samples and included genera (Leucobacter and Microbacterium) known to confer desiccation resistance in other hosts. Although Sea-Monkeys® taxonomy is unclear, phylogenetic inference of the cytochrome c oxidase I (COXI) gene from the host animal suggests Sea-Monkeys® belong to the Artemia franciscana 'superspecies'. Overall, Sea-Monkeys® kits appear to be a convenient and scalable mesocosm for the study of host-microbiome interactions and could serve as a useful tool for future invertebrate microbiome research, outreach, and education.

‘Altruistic’ cooperation among the prokaryotic community of Atlantic salterns assessed by metagenomics

Hypersaline environments are extreme habitats with a limited prokaryotic diversity, mainly restricted to halophilic or halotolerant archaeal and bacterial taxa adapted to highly saline conditions. This study attempts to analyze the taxonomic and functional diversity of the prokaryotes that inhabit a solar saltern located at the Atlantic Coast, in Isla Cristina (Huelva, Southwest Spain), and the influence of salinity on the diversity and metabolic potential of these prokaryotic communities, as well as the interactions and cooperation among the individuals within that community. Brine samples were obtained from different saltern ponds, with a salinity range between 19.5 % and 39 % (w/v). Total prokaryotic DNA was sequenced using the Illumina shotgun metagenomic strategy and the raw sequence data were analyzed using supercomputing services following the MetaWRAP and SqueezeMeta protocols. The most abundant phyla at moderate salinities (19.5–22 % [w/v]) were Methanobacteriota (formerly “Euryarchaeota”), Pseudomonadota and Bacteroidota, followed by Balneolota and Actinomycetota and Uroviricota in smaller proportions, while at high salinities (36–39 % [w/v]) the most abundant phylum was Methanobacteriota, followed by Bacteroidota. The most abundant genera at intermediate salinities were Halorubrum and the bacterial genus Spiribacter, while the haloarchaeal genera Halorubrum, Halonotius, and Haloquadratum were the main representatives at high salinities. A total of 65 MAGs were reconstructed from the metagenomic datasets and different functions and pathways were identified in them, allowing to find key taxa in the prokaryotic community able to synthesize and supply essential compounds, such as biotin, and precursors of other bioactive molecules, like β-carotene, and bacterioruberin, to other dwellers in this habitat, lacking the required enzymatic machinery to produce them. This work shed light on the ecology of aquatic hypersaline environments, such as the Atlantic Coast salterns, and on the dynamics and factors affecting the microbial populations under such extreme conditions.

Unveiling the influence of salinity on bacterial microbiome assembly of halophytes and crops

BackgroundClimate change and anthropogenic activities intensify salinity stress impacting significantly on plant productivity and biodiversity in agroecosystems. There are naturally salt-tolerant plants (halophytes) that can grow and withstand such harsh conditions. Halophytes have evolved along with their associated microbiota to adapt to hypersaline environments. Identifying shared microbial taxa between halophyte species has rarely been investigated. We performed a comprehensive meta-analysis using the published bacterial 16S rRNA gene sequence datasets to untangle the rhizosphere microbiota structure of two halophyte groups and non-halophytes. We aimed for the identification of marker taxa of plants being adapted to a high salinity using three independent approaches.ResultsFifteen studies met the selection criteria for downstream analysis, consisting of 40 plants representing diverse halophyte and non-halophyte species. Microbiome structural analysis revealed distinct compositions for halophytes that face high salt concentrations in their rhizosphere compared to halophytes grown at low salt concentrations or from non-halophytes. For halophytes grown at high salt concentrations, we discovered three bacterial genera that were independently detected through the analysis of the core microbiome, key hub taxa by network analysis and random forest analysis. These genera were Thalassospira, Erythrobacter, and Marinobacter.ConclusionsOur meta-analysis revealed that salinity level is a critical factor in affecting the rhizosphere microbiome assembly of plants. Detecting marker taxa across high-halophytes may help to select Bacteria that might improve the salt tolerance of non-halophytic plants.

Hourly to weekly variations in halite precipitation from the hypersaline Dead Sea: The role of evaporation, water cooling and freshwater plume stability

ABSTRACTThick‐bedded halite sequences in the geological record are characterized by lateral variations, reflecting spatiotemporal variations in environmental forcing. Although temporal variations have been examined over seasonal scales or longer durations, there is a paucity of information regarding the dynamics of halite deposition at shorter durations of days and hours. Additionally, the influence of water discharges and surface salinity gradients remains poorly understood. Here, for the first time, in situ, hourly to weekly halite accumulation rates were measured on the Dead Sea floor (ca 20 m water depth), the only modern deep and hypersaline water body. Novel underwater photography methods were developed to directly observe halite precipitation at the lake floor, coeval with monitoring of the environmental drives, i.e. evaporation, meteorological and limnological conditions. Two fundamental environments were explored: a diluted plume environment arising from spring discharge; and a mixed hypersaline environment. The focus was on deposition during winter when the halite accumulation rate is highest, and the relationship between evaporation and halite accumulation is most straightforward since the water column is vertically uniform. Significant spatial variations in halite accumulation were found between the two environments, along with hourly variations in each environment. In the mixed hypersaline environment, over intra‐diurnal timescales, evaporation plays a more significant role in halite precipitation, whereas temperature has a greater impact on seasonal changes. In the diluted plume environment, the stability of the buoyant plume controls the rate of halite deposition; during windstorms, the plume is stirred, with higher surface water salinity and higher rate of halite accumulation. However, under calm winds, the plume is stable, with diluted surface water, and the rate of halite accumulation is a few times lower. Following these new findings, the implications for the interpretation of halite deposits are discussed.

Isolation and Characterization of Plant Growth Promoting and Metal Resistant Archaea Associated with the Rhizosphere of Salsola stocksii and Atriplex amnicola

Halophilic microorganisms play a crucial role in plant health and growth in salinity affected lands. The objective of this study was to evaluate the haloarchaeal diversity from the rhizosphere of halophytes and plant growth promoting abilities of these strains. The whole genome sequences of two haloarchaeal strains, Halorubrum lacusprofundi HL1RP11 and Halobacterium noricense NRS2HaP9, were analyzed, and genes related to plant growth promoting traits were identified. Phylogenetic analysis showed that archaeal strains of Halococcus, Halorubrum, Halobacterium and Natrinema were dominant in the rhizosphere of halophytes. More than 60% of the strains were positive for phosphate solubilization and IAA production. About 33% were siderophore producers. More than 40% of haloarchaeal strains showed the heavy metal resistance for Nickel, Cadmium, Chromium and Zinc at a concentration of 5 mM. Genes involved in plant growth promotion were identified through annotation. Gene clusters related to secondary metabolites including phenazine, siderophore production and terpene were also identified in this study. Our results suggested that these haloarchaeal strains can be used as an eco-friendly biofertilizer to improve growth and productivity in hypersaline environment.

Transcriptomic profiling of haloarchaeal denitrification through RNA-Seq analysis.

Denitrification, a crucial biochemical pathway prevalent among haloarchaea in hypersaline ecosystems, has garnered considerable attention in recent years due to its ecological implications. Nevertheless, the underlying molecular mechanisms and genetic regulation governing this respiration/detoxification process in haloarchaea remain largely unexplored. In this study, RNA-sequencing was used to compare the transcriptomes of the haloarchaeon Haloferax mediterranei under oxic and denitrifying conditions, shedding light on the intricate metabolic alterations occurring within the cell, such as the accurate control of the metal homeostasis. Furthermore, the investigation identifies several genes encoding transcriptional regulators and potential accessory proteins with putative roles in denitrification. Among these are bacterioopsin-like transcriptional activators, proteins harboring a domain of unknown function (DUF2249), and cyanoglobin. In addition, the study delves into the genetic regulation of denitrification, finding a regulatory motif within promoter regions that activates numerous denitrification-related genes. This research serves as a starting point for future molecular biology studies in haloarchaea, offering a promising avenue to unravel the intricate mechanisms governing haloarchaeal denitrification, a pathway of paramount ecological importance.IMPORTANCEDenitrification, a fundamental process within the nitrogen cycle, has been subject to extensive investigation due to its close association with anthropogenic activities, and its contribution to the global warming issue, mainly through the release of N2O emissions. Although our comprehension of denitrification and its implications is generally well established, most studies have been conducted in non-extreme environments with mesophilic microorganisms. Consequently, there is a significant knowledge gap concerning extremophilic denitrifiers, particularly those inhabiting hypersaline environments. The significance of this research was to delve into the process of haloarchaeal denitrification, utilizing the complete denitrifier haloarchaeon Haloferax mediterranei as a model organism. This research led to the analysis of the metabolic state of this microorganism under denitrifying conditions and the identification of regulatory signals and genes encoding proteins potentially involved in this pathway, serving as a valuable resource for future molecular studies.

Ultra-rapid development of ‘solid’ aerobic granular sludge by stable transition/filling of inoculated ‘hollow’ mycelial pellets in hypersaline wastewater

To overcome the long start-up period in cultivating aerobic granular sludge (AGS) under hypersaline environment, mycelial pellets (MPs) of halotolerant fungus Cladosporium tenuissimum NCSL-XY8 were inoculated to try to realize the ultra-rapid development of salt-tolerant AGS by stable transition of ‘hollow’ MPs into ‘solid’ AGS without apparent fragmentation. The granules directly met the standard of AGS after inoculating MPs (Day 0), and it basically satisfied relatively strict standards of AGS (SVI30 < 50 mL/g, D50 > 300 μm, D10 > 200 μm and SVI30/SVI5 > 0.9) under anaerobic/aerobic mode during whole cultivation processes. Microstructure of the granular cross section clarified that MPs with hollow/loose inner layer transitioned into solid/dense AGS under anaerobic/aerobic mode within 7 days, while formed skin-like floating pieces and unstable double-layer hollow granules under aerobic mode. Organics removal reached relatively stable within 13 days under anaerobic/aerobic mode, 6 days faster than aerobic mode. This study provided a strategy for ultra-rapid and stable development of AGS, which showed the shortest granulation period in various AGS-cultivation strategies.

Isolation, Characterization and Identification of Halophilic bacteria from Solar saltern of Khambhat, Gujarat, India

The solar salterns of Khambhat, Gujarat are distinct biological niches distinguished by high salinity levels and harsh environmental circumstances. Our goal in this work was to isolate and characterise bacteria in order to investigate the diversity of microbes found in these saline soils. Standard microbiological procedures were used to isolate the bacteria from samples taken from various depths of the solar saltern ponds. To clarify their taxonomic identity and physiological characteristics, the isolated bacterial strains underwent morphological, biochemical and molecular characterization. Catalase, oxidase and fermentation assays are examples of biochemical studies that shed light on the isolated strains' metabolic capacities. Moreover, the phylogenetic relationships of the isolated bacteria were ascertained through molecular characterization using 16S rRNA gene sequencing. This work advances our knowledge of the microbial ecology of hypersaline environments and highlights the potential uses of bacteria isolated from these settings in biotechnology such as bioremediation, the synthesis of enzymes and the identification of new bioactive substances. To fully utilize these bacteria's biotechnological potential, more research into their functional properties is necessary.