Hypersaline Soils Research Articles

Metagenomic insights into the prokaryotic communities of heavy metal-contaminated hypersaline soils

Saline soils and their microbial communities have recently been studied in response to ongoing desertification of agricultural soils caused by anthropogenic impacts and climate change. Here we describe the prokaryotic microbiota of hypersaline soils in the Odiel Saltmarshes Natural Area of Southwest Spain. This region has been strongly affected by mining and industrial activity and feature high levels of certain heavy metals. We sequenced 18 shotgun metagenomes through Illumina NovaSeq from samples obtained from three different areas in 2020 and 2021. Taxogenomic analyses demonstrate that these soils harbored equal proportions of archaea and bacteria, with Methanobacteriota, Pseudomonadota, Bacteroidota, Gemmatimonadota, and Balneolota as most abundant phyla. Functions related to the transport of heavy metal outside the cytoplasm are among the most relevant features of the community (i.e., ZntA and CopA enzymes). They seem to be indispensable to avoid the increase of zinc and copper concentration inside the cell. Besides, the archaeal phylum Methanobacteriota is the main arsenic detoxifier within the microbiota although arsenic related genes are widely distributed in the community. Regarding the osmoregulation strategies, “salt-out” mechanism was identified in part of the bacterial population, whereas “salt-in” mechanism was present in both domains, Bacteria and Archaea. De novo biosynthesis of two of the most universal compatible solutes was detected, with predominance of glycine betaine biosynthesis (betAB genes) over ectoine (ectABC genes). Furthermore, doeABCD gene cluster related to the use of ectoine as carbon and energy source was solely identified in Pseudomonadota and Methanobacteriota.

Plant-associated bacteria and enzymes support Canavalia rosea growth in coastal hypersaline soils

Canavalia rosea is an extremophilic legume that grows in hypersaline and nutrient-deficient ecosystems. The extremophilic nature of C. rosea may be attributed to its ability to establish symbiotic associations with nutrient mineralizing and plant growth promoting (PGP) bacteria housed in the nodules. This study examined legume-microbe symbiosis and plant nutrition of C. rosea growing in subtropical coastal zone in KwaZulu-Natal province, South Africa. Canavalia rosea adult plants of the same age from Westbrook, Scottburgh and Durban were collected for plant biomass and plant nutrition and root nodules were used for bacterial extraction and identification. Rhizosphere soils sampled from the three localities were used for bacterial extraction and identification, extracellular enzyme assays and soil characteristics (pH, nutrient concentrations, total cation, and exchange acidity). Westbrook, Scottburgh and Durban soils were nutrient-deficient with varying total cations, acid saturation and a pH range of 7.3–7.6. Soil nutrient mineralizing extracellular enzyme activities varied across study sites. The culturable bacterial strains isolated from the sampled soils belonged to the Pseudomonas, Pantoea and Flavobacterium genera. Canavalia rosea root nodules were nodulated by Pseudomonas guariconensis, Pseudomonas fulva, Pseudomonas fluorescens, Pseudomonas chlororaphis and Pseudomonas chlororaphis subsp. aurantiaca. Plants growing in Westbrook soils had a significantly higher total plant biomass compared to Scottburgh and Durban plants. Plant P concentration did not vary significantly between sites while plant N and C concentrations varied significantly. Plant-associated and soil bacteria with phosphorus (P) solubilising, nitrogen (N) cycling, and N fixing functions and associated enzymes seem to facilitate the mobilization of nutrients enabling C. rosea to thrive in hypersaline and low-nutrient environments.

The Hypersaline Soils of the Odiel Saltmarshes Natural Area as a Source for Uncovering a New Taxon: Pseudidiomarina terrestris sp. nov.

The hypersaline soils of the Odiel Saltmarshes Natural Area are an extreme environment with high levels of some heavy metals; however, it is a relevant source of prokaryotic diversity that we aim to explore. In this study, six strains related to the halophilic genus Pseudidiomarina were isolated from this habitat. The phylogenetic study based on the 16S rRNA gene sequence and the fingerprinting analysis suggested that they constituted a single new species within the genus Pseudidiomarina. Comparative genomic analysis based on the OGRIs indices and the phylogeny inferred from the core genome were performed considering all the members of the family Idiomarinaceae. Additionally, a completed phenotypic characterization, as well as the fatty acid profile, were also carried out. Due to the characteristics of the habitat, genomic functions related to salinity and high heavy metal concentrations were studied, along with the global metabolism of the six isolates. Last, the ecological distribution of the isolates was studied in different hypersaline environments by genome recruitment. To sum up, the six strains constitute a new species within the genus Pseudidiomarina, for which the name Pseudidiomarina terrestris sp. nov. is proposed. The low abundance in all the studied hypersaline habitats indicates that it belongs to the rare biosphere in these habitats. In silico genome functional analysis suggests the presence of heavy metal transporters and pathways for nitrate reduction and nitrogen assimilation in low availability, among other metabolic traits.

Decoding the Genomic Profile of the Halomicroarcula Genus: Comparative Analysis and Characterization of Two Novel Species.

The genus Halomicroarcula, classified within the family Haloarculaceae, presently comprises eight haloarchaeal species isolated from diverse saline habitats, such as solar salterns, hypersaline soils, marine salt, and marine algae. Here, a detailed taxogenomic study and comparative genomic analysis of the genus Halomicroarcula was carried out. In addition, two strains, designated S1CR25-12T and S3CR25-11T, that were isolated from hypersaline soils located in the Odiel Saltmarshes in Huelva (Spain) were included in this study. The 16S rRNA and rpoB' gene sequence analyses affiliated the two strains to the genus Halomicroarcula. Typically, the species of the genus Halomicroarcula possess multiple heterogeneous copies of the 16S rRNA gene, which can lead to misclassification of the taxa and overestimation of the prokaryotic diversity. In contrast, the application of overall genome relatedness indexes (OGRIs) augments the capacity for the precise taxonomic classification and categorization of prokaryotic organisms. The relatedness indexes of the two new isolates, particularly digital DNA-DNA hybridization (dDDH), orthologous average nucleotide identity (OrthoANI), and average amino acid identity (AAI), confirmed that strains S1CR25-12T (= CECT 30620T = CCM 9252T) and S3CR25-11T (= CECT 30621T = CCM 9254T) constitute two novel species of the genus Halomicroarcula. The names Halomicroarcula saliterrae sp. nov. and Halomicroarcula onubensis sp. nov. are proposed for S1CR25-12T and S3CR25-11T, respectively. Metagenomic fragment recruitment analysis, conducted using seven shotgun metagenomic datasets, revealed that the species belonging to the genus Halomicroarcula were predominantly recruited from hypersaline soils found in the Odiel Saltmarshes and the ponds of salterns with high salt concentrations. This reinforces the understanding of the extreme halophilic characteristics associated with the genus Halomicroarcula. Finally, comparing pan-genomes across the twenty Halomicroarcula and Haloarcula species allowed for the identification of commonalities and differences between the species of these two related genera.

EC conversion for 1:5 extracts and standard saturated soil–water pastes in the assessment of arid land salinization: Classical methodologies revisited

The common assessment of soil salinity posits a linear function, which transfers the electrical conductivity (EC) of highly diluted extracts to the standard state of soil paste. Our study examines this assumption and explains its limitations in a wide range of EC for highly saline soils of the Aral region in Uzbekistan. For a comparative EC assessment in the liquid phase from standard soil pastes and 1:5 aqueous extracts we used portable EC–meters. The dependences of EC, total dissolved solids (TDS), and soil–water potential on the pore water content were evaluated using centrifugation to separate the liquid phase from the soil matrix. The non-linearity of the relationship between the EC of water from soil pastes and 1:5 water extracts for both average and median data over a broad (0.4–160 dS/m) range of their variation is detected. A strong retention and concentration of electrolytes in fine pores and water films resistant to vacuum extraction, as well as the nonlinear EC versus TDS relationship in highly saline soils are attributed to this nonlinearity. A comprehensive statistical analysis showed that despite the general non-linearity, in the EC range from 0 to 30–35 dS/m, the results for 1:5 extract can be reliably converted to the standard state using the dilution model for the liquid phase of the soil with one basic parameter of soil bulk density. For hypersaline soils (EC > 30–35 dS/m), conversion based on the dilution theory is unacceptable due to a strong underestimation of TDS.

Halotolerant Bacillus Species as Plant Growth Promoting Rhizobacteria from Hyper – Arid Area of Algeria

The aim of this study was to determine the diversity of aerobic halophilic and halotolerant Bacillus (AHHB) Plant Growth Promoting Rhizobacteria (PGPR), producing hydrolytic exo-enzymes and their inoculation effect in on two cowpea plants. Therefore, soil dilution plate technique was performed on Tryptic Soy Agar complemented with a thermal pretreatment to select Bacillus strains associated to Phoenix dactylifera rhizosphere growing in hypersaline and arid soil of Algeria (In Salah, Tamanrasset). The inoculation effect of these strains on cowpea plants growth was assessed based on biometric and physiological parameters. As results, thirteen halophilic, halotolerant and non-halophilic Bacillus strains were isolated. Upon screening, all strains are capable of producing at least two hydrolytic enzymes under saline conditions and most of the strains (n=10/13) showed at least two PGP traits. Strains were identified based on their phenotypic and biochemical characteristics as members of Bacillus genera. The inoculation of these strains in cowpeas had significantly improve biometrics and physiological growth parameters of inoculated plant. Based on general plant aspect, four strains are distinguished: RP 7 (B. coagulans), RP 8 (B. circulans), RP 10 (Paenibacillus polymyxa) and RP 12 (B. circulans). The isolation and characterization of halophilic and halotolerant Bacillus strains has increased knowledge of the rhizocompetent bacterial community associated with date palm in saline and arid soils. AHHB have proven to be highly effective strains to improve cowpea plant growth and development.

Characterization of Haloarcula terrestris sp. nov. and reclassification of a Haloarcula species based on a taxogenomic approach.

An extremely halophilic archaeon, strain S1AR25-5AT, was isolated from a hypersaline soil sampled in Odiel Saltmarshes Natural Area (Huelva, Spain). The cells were Gram-stain-negative, motile, pleomorphic rods. Cell growth was observed in the presence of 15-30 % (w/v) NaCl [optimum, 25 % (w/v) NaCl], at pH 6.0-9.0 (optimum, pH 6.5-7.5) and at 25-50 °C (optimum, 37 °C). Based on the 16S rRNA and rpoB' gene sequence comparisons, strain S1AR25-5AT was affiliated to the genus Haloarcula. Taxogenomic analysis, including comparison of the genomes and the phylogenomic tree based on the core-orthologous proteins, together with the genomic indices, i.e., orthologous average nucleotide identity, digital DNA-DNA hybridization and average amino acid identity, confirmed that strain S1AR25-5AT (=CCM 9249T=CECT 30619T) represents a new species of the genus Haloarcula, for which we propose the name Haloarcula terrestris sp. nov. The major polar lipids were phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester, phosphatidylglycerol sulphate and an unidentified glycolipid, which correlated with the lipid profile of species of the genus Haloarcula. In addition, based on the modern approach in description of species in taxonomy of prokaryotes, the above mentioned genomic indexes indicated that the species Haloarcula tradensis should be considered as a heterotypic synonym of Haloarcula argentinensis.

Aromatic compounds depurative and plant growth promotion rhizobacteria abilities of Allenrolfea vaginata (Amaranthaceae) rhizosphere microbial communities from a solar saltern hypersaline soil

IntroductionThis work investigates whether rhizosphere microorganisms that colonize halophyte plants thriving in saline habitats can tolerate salinity and provide beneficial effects to their hosts, protecting them from environmental stresses, such as aromatic compound (AC) pollution.MethodsTo address this question, we conducted a series of experiments. First, we evaluated the effects of phenol, tyrosine, 4-hydroxybenzoic acid, and 2,4-dichlorophenoxyacetic (2,4-D) acids on the soil rhizosphere microbial community associated with the halophyteAllenrolfea vaginata. We then determined the ability of bacterial isolates from these microbial communities to utilize these ACs as carbon sources. Finally, we assessed their ability to promote plant growth under saline conditions.ResultsOur study revealed that each AC had a different impact on the structure and alpha and beta diversity of the halophyte bacterial (but not archaeal) communities. Notably, 2,4-D and phenol, to a lesser degree, had the most substantial decreasing effects. The removal of ACs by the rhizosphere community varied from 15% (2,4-D) to 100% (the other three ACs), depending on the concentration.Halomonasisolates were the most abundant and diverse strains capable of degrading the ACs, with strains ofMarinobacter,Alkalihalobacillus,Thalassobacillus,Oceanobacillus, and the archaeaHaladaptatusalso exhibiting catabolic properties. Moreover, our study found that halophile strains Halomonas sp. LV-8T andMarinobactersp. LV-48T enhanced the growth and protection ofArabidopsis thalianaplants by 30% to 55% under salt-stress conditions.DiscussionThese results suggest that moderate halophile microbial communities may protect halophytes from salinity and potential adverse effects of aromatic compounds through depurative processes.

Isolation and Characterization of Culturable Osmotolerant Microbiota in Hypersaline and Hypergypsic Soils as New Treatment for Osmotic Stress in Plants

Saline and gypsic soils impede or condition the establishment of farms in many regions worldwide. Stress caused by the accumulation of sodium or calcium ions in the soil drastically limits plant growth and is a limiting factor in the production of many crops. For this reason, saline and gypsic soils were preferentially exploited for mineral extraction. However, nowadays, they can be a source of new biotechnological tools to help in the osmotic stress to which some crops are exposed. In these environments, despite being traditionally characterized by their low biodiversity, we can find well-adapted microbiota that may be able to interact with plants to deal with different environmental stresses. These mechanisms may consist of a very important contribution to the development of new osmotic stress-dealing bioinoculants. The present study sought to elucidate the diversity of the cultivable population of such environments and use them as regulators of soil nutrients and stress-relieving symbionts in plants under osmotic stress. Among the candidate strains selected to cover more scenarios, we found that the strains Stutzerimonas stutzeri A38 and Bacillus pumilus A49 were able to increase root size under osmotic stress in Medicago sativa and Medicago polymorpha plants. Moreover, Peribacillus frigoritolerans A70 and Bacillus licheniformis A46 also enhanced the performance in M. polymorpha, showing interesting potential for a future use in wasteland use for production to livestock feeding or other relevant industries.

Natrinema salsiterrestre sp. nov., an extremely halophilic archaeon isolated from a hypersaline soil.

An extremely halophilic archaeal strain, designated S1CR25-10T, was isolated from hypersaline soil sampled in the Odiel Saltmarshes Natural Area in Southwestern Spain (Huelva) and subjected to a polyphasic taxonomic characterization. The cells were Gram-stain-negative, motile and their colonies were pink-pigmented. It was a strictly aerobic haloarchaeon that could grow at 25-55 °C (optimum, 37 °C), at pH 6.0-9.0 (optimum, pH 7.0-8.0) and in the presence of 12-30 % (w/v) total salts (optimum, 20-25 %, w/v). The phylogenetic analysis based on the comparison of the 16S rRNA gene sequences revealed that strain S1CR25-10T belongs to the genus Natrinema, with 98.9 % similarity to Natrinema salinisoli SLN56T. In addition, the values of orthologous average nucleotide identity, digital DNA-DNA hybridization and average amino acid identity were below the threshold limits accepted for prokaryotic species delineation, with N. salinisoli SLN56T showing the highest relatedness values (92.6 % and 48.4 %, respectively). The major polar lipids were phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester, phosphatidylglycerol sulfate and a glycolipid chromatographically identical to sulfated diglycosyl diether. The DNA G+C content of the isolate was 63.8 mol%. Based on the phylogenetic, phenotypic and chemotaxonomic characterization and the whole genome results, strain S1CR25-10T represents a new species within the genus Natrinema, for which the name Natrinema salsiterrestre sp. nov., with type strain S1CR25-10T (=CECT 30623T=CCM 9251T), is proposed.

Bioremediation of two oil-contaminated Kuwaiti hyper-saline soils by cross bioaugmentation and the role of indigenous halophilic/halotolerant hydrocarbonoclastic bacteria

Hyper-saline evaporitic sandflats known as Sabkhas occur in areas prone to oil contamination throughout the Gulf states. Bioaugmentation of Sabkha environments using enrichments of indigenous microorganisms is a potential means of ameliorating oil pollution. Two soil samples from the north and south Kuwaiti Sabkhas were contaminated with 5% w/w oil to prepare inocla enriched with hydrocarbonoclastic bacteria. Inocula were then used in a 6-month cross-bioaugmentation process to assess oil bioremediation in two artificially oil-contaminated soils collected from the same Sabkhas. Although the numbers of hydrocarbonoclastic bacteria increased and oil degradation was observed in both unbioaugmented and bioaugmented samples for both locations, bioaugmentation significantly enhanced degradation at only one location. The predominant culturable strain Bacillus oceanisediminis in the enriched inocula failed to colonize the bioaugmented soils in both locations. For further insight into oil biodegradation by Sabkha bacteria, sixteen hydrocarbonoclastic isolates were recovered and their oil biodegradation potential was recognized under different salinity conditions. All isolates tolerated up to 10% w/v salinity and most still grew at up to 18% and showed maximum oil consumption at their optimal salinity requirement. To simulate a serious pollution event, the potential response of Sabkha soils after high oil contamination reached 20% was tested, and this indicated both soils showed a significant self-cleaning potential at this high pollutant level. Overall, we conclude that bioremediation of contaminated hyper-saline soils depends mainly on the allochthonous halotolerant/halophilic hydrocarbonoclastic bacteria adapted to their native area, and the potential for microbial bioremediation even under high contamination levels is potentially high.

A step into the rare biosphere: genomic features of the new genus Terrihalobacillus and the new species Aquibacillus salsiterrae from hypersaline soils.

Hypersaline soils are a source of prokaryotic diversity that has been overlooked until very recently. The phylum Bacillota, which includes the genus Aquibacillus, is one of the 26 phyla that inhabit the heavy metal contaminated soils of the Odiel Saltmarshers Natural Area (Southwest Spain), according to previous research. In this study, we isolated a total of 32 strains closely related to the genus Aquibacillus by the traditional dilution-plating technique. Phylogenetic studies clustered them into two groups, and comparative genomic analyses revealed that one of them represents a new species within the genus Aquibacillus, whereas the other cluster constitutes a novel genus of the family Bacillaceae. We propose the designations Aquibacillus salsiterrae sp. nov. and Terrihalobacillus insolitus gen. nov., sp. nov., respectively, for these two new taxa. Genome mining analysis revealed dissimilitude in the metabolic traits of the isolates and their closest related genera, remarkably the distinctive presence of the well-conserved pathway for the biosynthesis of molybdenum cofactor in the species of the genera Aquibacillus and Terrihalobacillus, along with genes that encode molybdoenzymes and molybdate transporters, scarcely found in metagenomic dataset from this area. In-silico studies of the osmoregulatory strategy revealed a salt-out mechanism in the new species, which harbor the genes for biosynthesis and transport of the compatible solutes ectoine and glycine betaine. Comparative genomics showed genes related to heavy metal resistance, which seem required due to the contamination in the sampling area. The low values in the genome recruitment analysis indicate that the new species of the two genera, Terrihalobacillus and Aquibacillus, belong to the rare biosphere of representative hypersaline environments.

Thrive or survive: prokaryotic life in hypersaline soils

BackgroundSoil services are central to life on the planet, with microorganisms as their main drivers. Thus, the evaluation of soil quality requires an understanding of the principles and factors governing microbial dynamics within it. High salt content is a constraint for life affecting more than 900 million hectares of land, a number predicted to rise at an alarming rate due to changing climate. Nevertheless, little is known about how microbial life unfolds in these habitats. In this study, DNA stable-isotope probing (DNA-SIP) with 18O-water was used to determine for the first time the taxa able to grow in hypersaline soil samples (ECe = 97.02 dS/m). We further evaluated the role of light on prokaryotes growth in this habitat.ResultsWe detected growth of both archaea and bacteria, with taxon-specific growth patterns providing insights into the drivers of success in saline soils. Phylotypes related to extreme halophiles, including haloarchaea and Salinibacter, which share an energetically efficient mechanism for salt adaptation (salt-in strategy), dominated the active community. Bacteria related to moderately halophilic and halotolerant taxa, such as Staphylococcus, Aliifodinibius, Bradymonadales or Chitinophagales also grew during the incubations, but they incorporated less heavy isotope. Light did not stimulate prokaryotic photosynthesis but instead restricted the growth of most bacteria and reduced the diversity of archaea that grew.ConclusionsThe results of this study suggest that life in saline soils is energetically expensive and that soil heterogeneity and traits such as exopolysaccharide production or predation may support growth in hypersaline soils. The contribution of phototrophy to supporting the heterotrophic community in saline soils remains unclear. This study paves the way toward a more comprehensive understanding of the functioning of these environments, which is fundamental to their management. Furthermore, it illustrates the potential of further research in saline soils to deepen our understanding of the effect of salinity on microbial communities.

Special Issue “Halophilic Microorganisms”

Hypersaline environments are mainly represented by aquatic systems, such as solar salt ponds or natural salt lakes, as well as by the sediments of these hypersaline aquatic ecosystems and soils with high salt content [...].

Biotin pathway in novel Fodinibius salsisoli sp. nov., isolated from hypersaline soils and reclassification of the genus Aliifodinibius as Fodinibius.

Hypersaline soils are extreme environments that have received little attention until the last few years. Their halophilic prokaryotic population seems to be more diverse than those of well-known aquatic systems. Among those inhabitants, representatives of the family Balneolaceae (phylum Balneolota) have been described to be abundant, but very few members have been isolated and characterized to date. This family comprises the genera Aliifodinibius and Fodinibius along with four others. A novel strain, designated 1BSP15-2V2T, has been isolated from hypersaline soils located in the Odiel Saltmarshes Natural Area (Southwest Spain), which appears to represent a new species related to the genus Aliifodinibius. However, comparative genomic analyses of members of the family Balneolaceae have revealed that the genera Aliifodinibius and Fodinibius belong to a single genus, hence we propose the reclassification of the species of the genus Aliifodinibius into the genus Fodinibius, which was first described. The novel strain is thus described as Fodinibius salsisoli sp. nov., with 1BSP15-2V2T (=CCM 9117T = CECT 30246T) as the designated type strain. This species and other closely related ones show abundant genomic recruitment within 80-90% identity range when searched against several hypersaline soil metagenomic databases investigated. This might suggest that there are still uncultured, yet abundant closely related representatives to this family present in these environments. In-depth in-silico analysis of the metabolism of Fodinibius showed that the biotin biosynthesis pathway was present in the genomes of strain 1BSP15-2V2T and other species of the family Balneolaceae, which could entail major implications in their community role providing this vitamin to other organisms that depend on an exogenous source of this nutrient.

Salt accumulation in soils under furrow and drip irrigation using modified waters in Central Iran

The objectives of this study were i) to characterize the water and soils under different managements, ii) to evaluate the sustainability of using hypersaline soils and water, and iii) to assess possible solutions to prevent more degradation of soil and water resources. Field and laboratory analysis of the samples using eight pedons and 128 surface samples taken from grid in four pre-determined land uses; pistachio orchard abandoned, pistachio orchard with furrow irrigation, wheat and maize cropping with furrow irrigation, pistachio orchard with drip irrigation. The study area, 170 ha, comprised two distinct soil parent materials including marls (max. ECe >100 dS/m) and alluviums (max. ECe >60 dS/m). Abandoning lands caused salinity increasing due to lack of leaching by irrigation water. The maximum increase of soil salinity was in the abandoned land use (EC e =98 dS/m), where trees had been removed and there is no irrigation, followed by pistachio plantation land use (EC=11 to 34 dS/m), and wheat and maize cropping land use (EC=11-19 dS/m). The minimum rise in soil salinity was in the drip irrigation due to mixing freshwater with saline water and therefore better water quality (EC=3 dS/m at surface layer and 17 dS/m in next layer). Land use change to agriculture increased the need for irrigation and because of arid climate it mainly supplied by groundwater from deep wells. Using deep groundwater due to rock-water reaction and increasing salinity, decreased water quality in furrow irrigation and therefore it had more significant effect on soil salinity compare to drip. Comparison of the mean values of soil salinity indicators in 2018 showed that salinity has increased by 3-6 times in the furrow irrigation and at least two-fold in the drip irrigation, compared to 2002. The calculated salinity indicators also proved the soil and water resources had been degraded and present land use types are not sustainable. Possible solutions could be to minimize land use change to agriculture, to use drip irrigation with mixed saline and freshwater, and to remove salt crusts from the soil surface.

Metagenomic Insights into Microbial Community Structure, Function, and Salt Adaptation in Saline Soils of Arid Land, China.

Soil salinization is spread in the dryland of NW China due to the dry or extreme dry climate. Increased salinization damages the health and function of soil systems and influences the microbial community structure and function. Some studies have been conducted to reveal the microbial community structure and isolate the microorganisms of saline soil or salt-lake sediments in this region. However, the functions of microorganisms and their response to salinization, i.e., their adaptation strategy to a wide salinization range in arid environments, are less understood. Here, we applied metagenomics technology to investigate the microbial community structure, function, and their relationship with salinization, and discussed the adaptative strategy of microorganisms to different saline environments. A total of 42 samples were sequenced on the Illumina PE500 platform. The archaea and bacteria constituted the dominant kingdoms; Actinobacteria, Proteobacteria, Bacteroidetes, and Firmicutes were the dominant bacterial phyla; and Euryarchaeota were the dominant archaeal phylum. The microbial communities showed significant structure divergence according to the salt concentration (saline (mean EC 22 mS/cm) and hypersaline (mean EC 70 mS/cm)), wherein the communities were dominated by bacteria in saline soils and archaea in hypersaline soils. Most of the dominant bacterial representation decreased with salinity, while the archaea increased with salinity. KEGG functional annotation showed that at level 2, the cell motility, environmental adaptation, signal transduction, signaling molecules and interaction, glycan biosynthesis and metabolism, and metabolism of other amino acids were reduced from saline to hypersaline, whereas the metabolism of cofactors and vitamins, folding sorting and degradation, replication and repair, transcription and translation, amino acid biosynthesis, glycolysis/gluconeogenesis, and carbon fixation increased with salinity. The increased salt content decreased the carbohydrate activities of microorganisms. The osmolyte regulation substance synthesis and absorption-related genes were more abundant in saline soils than in hypersaline soils, whereas the Na+/H+ antiporter genes (mnhB-E) and H+/Na+-transporting ATPase genes (atpA-F, I, K) were significantly higher in hypersaline soils. This indicated that in saline soils, microorganisms primarily synthesize and/or uptake compatible solutes to cope with osmotic stress, whereas in the hypersaline habitat, the high-salt-in strategy was predicated to be adopted by the halophilic/extremely halophilic microorganisms, coupled with a high abundance of replication and repair, cofactors and vitamin metabolism, nucleotide metabolism, and carbon fixation to provide energy and ensure cell regeneration. In conclusion, increases in salinity influence the microbial communities' structure and function, as well as the adaptation of microorganisms.

Enzyme Profiling and Identification of Endophytic and Rhizospheric Bacteria Isolated from Arthrocnemum macrostachyum.

Endophytic and rhizospheric bacteria isolated from halophytic plants support their host to survive in hyper-saline soil. These bacteria are also known to produce various enzymes with potential industrial applications. In this study, the endophytic and rhizospheric bacteria were isolated from Arthrocnemum macrostachyum collected from Karachi, Pakistan, and their ability to produce various extracellular enzymes was assessed using commercial and natural substrates. In total, 11 bacterial strains were isolated (four endophytic; seven rhizospheric). Bacillus was found to be the most abundant genus (73%), followed by Glutamicibacter (27%). The isolates including Glutamicibacter endophyticus and Bacillus licheniformis are reported for the first time from A. macrostachyum. All of the isolates were capable of producing at least two of the five industrially important hydrolytic enzymes tested, i.e., xylanase, cellulase, amylase, pectinase, and lipase. Lipase production was found to be highest among the isolates, i.e., up to 18 IU mL-1. Although most of the isolates could grow at a wide range of temperatures (4-55 °C), pH (1-11), and salt concentrations (2-12%), under extreme conditions, very little growth was observed and the optimal growth was recorded between 2% and 6% NaCl, 25 and 45 °C, and 7 and 9 pH. Our results suggest that these isolates could be potential producers of enzymes with several biotechnological applications.

Unraveling the enzymatic and antibacterial potential of rare halophilic actinomycetes from Algerian hypersaline wetland ecosystems.

The study aimed to isolate rare halophilic actinomycetes from hypersaline soils of Algerian inland Wetland Ecosystems "Sebkhas-Chotts" located in arid and hot hyperarid lands with international importance under the Ramsar Convention and to explore their enzyme-producing and antibacterial abilities. The halophilic actinomycetes were selectively isolated using agar-rich media supplemented with 5, 10, and 15% (W/V) of total salts. Thirty-one isolates were obtained and 16S rRNA gene sequencing analysis revealed the presence of members affiliated to rare halophilic actinobacterial genera (Actinopolyspora and Nocardiopsis) accounting for 74.19% (23 isolates out of 31) and 25.8% (8 isolates), respectively. Both phylotypes are alkalitolerant and halophilic thermotolerant actinomycetes displaying significant hydrolytic activities relative to (amylase, asparaginase, cellulase, esterase, glutaminase, inulinase, protease, pectinase, xylanase), and over 96% of tested isolates exhibited all common enzymes, mainly active at 10% of growing salt. In addition, high antibacterial activity was observed against Bacillus cereus, Bacillus subtilis, Micrococcus luteus, and Staphylococcus aureus. The findings showed that saline wetlands ecosystems represent a rich reservoir for the isolation of significant rare halophilic actinomycetes with potential adaptive features and valuable sources for novel bioactive metabolites and biocatalysts of biotechnological interest.

Discovery of novel enzymes from extreme environments through metagenomic approaches: A mini-review

Extremophilic microorganisms are able to survive under extreme conditions of temperature, pH, salinity and pressure, such as hypersaline soils, hydrothermal vents, acidic coal mines and soda lakes. These microorganisms have special genetic and physiological modifications to survive under abiotic and biotic stresses. Extremozymes are considered as an important source for different industrial and biotechnological applications. With the advent of meta-omics approaches, the discovery of novel enzymes has accelerated. Using function- and sequence-based metagenomics, a large number of enzymes have been identified and characterized directly from extreme environments. Many extremozymes such as proteases, amylases, esterases, cellulases, chitinases, oxidoreductases and hydrolases have special properties to work at a wide range of salt, pH and temperature. In this review, the discovery and industrial applications of novel enzymes from extreme environments through metagenomic approaches have been discussed. We have also explained the screening methods of novel extremozymes through function- and sequence-based metagenomics.