High Salinity Stress Research Articles

Regulatory Effects of S-Abscisic Acid and Soil Conditioner on the Yield and Quality of Hybrid Rice Under Salt Stress

Salt stress significantly reduces rice yield and deteriorates rice quality. The present study was conducted to explore the regulatory effects of sole and combined application of S-abscisic acid (S-ABA) and soil conditioner on rice under high salt stress. The experimental treatments comprised 0.1% S-ABA alone (T1), the application of soil conditioner (T2), the combined application of both S-ABA and halotolerant microorganism soil conditioner (T3), and a control without any regulatory substance (CK). The treatments were arranged in a randomized complete block design in triplicate. To simulate high salinity stress, a 0.6% saltwater solution (by mixing natural seawater with freshwater) was used for irrigation. The results showed that T3 alleviated the phytotoxic effects of high salt stress and substantially improved rice yield. Furthermore, the numbers of effective panicles, grains per panicle, and 1000-grain weight under T3 treatment were 13.3–14.5%, 8.9–14.1%, and 4.9–5.5% higher than CK owing to improvement in dry matter accumulation, SPAD values, leaf area index, antioxidant enzyme activity, and reduced malondialdehyde and sodium ion content in rice. Moreover, the T3 treatment increased the output, output rate, and conversion rate of stem sheath matter after the heading stage; improved the milling yield, starch paste viscosity, starch stickiness, and gelatinization enthalpy; and reduced rice chalkiness. In addition, the T3 treatment also increased the amylose contents and decreased the total protein contents, thereby improving the taste of the rice. Overall, the results indicated that the application of exogenous S-ABA and soil conditioner is an effective strategy to alleviate the severity of salt stress in rice.

Effect of salinity on nitrogen removal performance, enzymatic activity and metabolic pathway of Chlorella pyrenoidosa treating aquaculture wastewater.

The nitrogen removal performance, enzymatic activity, antioxidant response and metabolic pathway of Chlorella pyrenoidosa (C. pyrenoidosa) under different salinities have been investigated during the treatment of aquaculture wastewater. The growth, chlorophyll content and photosynthetic activity of C. pyrenoidosa were negatively correlated with the salinity from 1% to 3%. The removal performance of chemical oxygen demand (COD) and nitrogen compounds for C. pyrenoidosa decreased with the increase of salinity from 1% to 3%, which was due to the decrease of their corresponding metabolism enzymatic activities. The equilibrium between the reactive oxygen species production and antioxidant defensive system in C. pyrenoidosa was destroyed under high salinity stress and then caused an irreversible damage, which decreased the nitrogen assimilation of C. pyrenoidosa. The metabolic pathway of C. pyrenoidosa under 3% salinity had some obvious variation by comparison with 1% salinity, which led to the discrepancy in the microalgae activity and nitrogen transformation performance. Additionally, high salinity could inhibit the expression of gene associated with the chlorophyll synthesis and damaged the photosystem II reaction center. This study can provide an insight into the effect of salinity on the nitrogen removal from aquaculture wastewater by microalgae.

Growth of Picochlorum celeri in produced water from the Permian Basin (US)

Produced water generated from hydraulic fracking is a waste stream that, on one hand, demands remediation, and, on the other hand, can be used as a water source to support a circular economy. In this study, we aimed to assess the ability of Picochlorum celeri to grow in two different sources of raw, untreated produced water collected in New Mexico, USA. The produced water had initial salinities of 110 and 140 PPT. Picochlorum was screened, with additional algae, on two different sources of produced water supplemented with nitrogen and phosphorus. The strain was able to grow on 25 % and 50 % produced water and achieve biomass densities between ~40 and 100 % of those demonstrated by control cultures. To separate the effects of high salinity stress from toxicity of the produced water samples, we conducted a bioassay with produced water under isotonic conditions of 60 PPT. When controlling for salinity, the contaminants associated with the two sources of produced water did not affect growth of the algae. This study provides justification to consider P. celeri as a candidate for remediation of and biomass production on produced water. Foundational studies are necessary to assess remediation potential and characterize the growth, biomass accumulation, and biomass composition of P. celeri grown on a variety of produced water streams.

Effects of Exogenous Boron on Salt Stress Responses of Three Mangrove Species.

Salt stress is common but detrimental to plant growth, even in mangroves that live in saline areas. Boron (B) is an essential micronutrient that performs an important role in many functions in plants; however, its protective role under salt stress is poorly understood, especially in long-lived woody plants. In this study, we conducted an indoor experiment under simulated tidal conditions with four treatments (10‱ salinity, 40‱ salinity, 40‱ salinity + 100 μM B, and 40‱ salinity + 500 μM B) and three mangrove species (Avicennia marina, Aegiceras corniculatum, and Bruguiera gymnorrhiza) to investigate the effects of exogenous B on salt tolerance in plant growth, morphology, physiology, and leaf anatomy. The results showed that exogenous low-concentration B treatment (100 μM B) improved the performance of mangrove species under high salinity stress, especially in terms of physiology and leaf anatomy, while high-concentration B treatment (500 μM B) had adverse effects. Additionally, we found that the response to exogenous B varied among species in physiology and leaf anatomy, such as proline, malondialdehyde, activity of antioxidant enzymes, palisade tissue, and spongy tissue, which may be related to the salt tolerance of different species. This study may provide useful insights into the alleviation of salt stress by B in mangrove growth and development, which may facilitate mangrove cultivation and afforestation in a saline environment.

Study on the synergistic mechanism of proline in the treatment of high-salt phenolic wastewater by short-time aerobic digestion process.

High salt concentrations pose a significant challenge to the efficiency of activated sludge (AS) in phenolic wastewater treatment. As a cellular osmoprotectant, proline (Pro) has the capacity to increase the salt tolerance of microbes in AS, hence improving the efficiency of phenolic wastewater degradation. Nevertheless, the precise mechanism behind this enhancement remains ambiguous. This study utilized short-time aerobic digestion (STAD) to examine the kinetics of phenol degradation (250-750mg/L) by AS under high-salinity stress (2-8%), with the inclusion of Pro (115-575mg/L) as an auxiliary agent. The process was optimized via response surface methodology (RSM), and the mitigating effect of Pro on microorganisms in AS subjected to salt stress was evaluated. The results demonstrated that the addition of 468mg/L Pro substantially improved the ability of AS to withstand high-salinity wastewater with high phenol concentrations, which had a salinity of 5.1% and a phenol concentration of 531mg/L. The addition led to a mitigation rate of the phenol degradation constant k0 of 38.59 ± 1.54%, resulting in enhanced degradation of chemical oxygen demand (COD), NH4+-N, and NO3--N. In addition, the prolonged presence of Pro increased AS dehydrogenase activity (DHA) by 24.82% after 30days. Microbial community analysis demonstrated that Pro promoted the proliferation of functional microorganisms such as Proteobacteria, Firmicutes, Acinetobacter, and Comamonas. These bacteria have essential functions in the elimination of phenol and organic matter, as well as the absorption of nitrogen. This study emphasizes the impact of Pro as a compatible solute in the treatment of high-salinity and high-phenol wastewater in the STAD process.

Over Expression of the Carbonic Anhydrase Gene Confers Salinity Tolerance with Improved Yield in Rice

Background: Abiotic and biotic stresses impact agricultural productivity. Rice being the stable food of India; requires more scientific intervention to boost productivity. Methods: Cloning and transformation of carbonic anhydrase (CA) gene in IR64 rice, molecular analysis of T1 transgenic CA rice plants, salinity tolerance index, leaf disk senescence assay, chlorophyll content, biochemical analysis of antioxidant activities of marker-free CA transgenic lines and measurement of photosynthetic activities and agronomic characteristics of CA transgenic plants were conducted. Result: We have raised two (2) lines of marker free CA overexpressing transgenic rice (Oryza sativa L. cv. IR64) plants. The overexpression of CA driven by CaMV35S promoter in transgenic rice confers high salinity (200 mM NaCl) stress tolerance in the rice. Photosynthetic characteristics such as net photosynthetic rate (PN), stomatal conductance (gs), intercellular CO2 (Ci), as well as chlorophyll (Chl) contents were significantly (22-31%) higher in transgenic lines under salinity stress as compared to control plants. Ascorbate peroxidase (APX), superoxide dismutase (SOD), glutathione reductase (GR) and guaiacol peroxidase (GPX) were significantly higher (21-37%) in transgenics as compared with VC and WT plants. Overall, the present research is focused to develop marker free CA overexpressing transgenic lines for better tolerance against salinity stress, higher photosynthesis and better productivity.

Transcriptome analysis provides preliminary insights into the response of Sepia esculenta to high salinity stress

Sepia esculenta is an economically important cephalopod species contributing to aquaculture in China. Global climate changes have increased fluctuations in the ocean salinity level, which is a major problem for S. esculenta populations because extreme changes in salinity may be fatal to marine life. In this study, S. esculenta larvae were subjected to high salinity stress to investigate their stress resistance mechanisms. High-throughput transcriptome sequencing technology was used to detect transcript-level changes in samples. A total of 1,126 significant differentially expressed genes were identified. The results of functional enrichment analyses showed that high salinity activated apoptosis and several innate immunity-related pathways in S. esculenta larvae. On the basis of a protein-protein interaction network analysis, PARP1, PIK3CB, and FLNA were identified as hub genes involved in larval resistance to high salinity. Quantitative real-time PCR technology was used to analyze gene expression and verify the accuracy of the transcriptome sequencing results. The process of apoptosis can restrict high salinity-induced tissue damage, while the activation of an inflammatory response can maintain cellular homeostasis. Therefore, we speculate that high salinity induces innate immunity and apoptosis in S. esculenta larvae and modulates growth and development. The study findings also suggest that aquaculture losses due to increased seawater salinity must be prevented in artificial aquaculture systems.

SORTING NEXIN1 facilitates SALT OVERLY SENSITIVE1 protein accumulation to enhance salt tolerance in Arabidopsis.

The plasma membrane (PM)-localized Na+/H+ antiporter Salt Overly Sensitive1 (SOS1) is essential for plant salt tolerance through facilitating Na+ efflux; however, how SOS1 localization and protein accumulation is regulated in plants remains elusive. Here, we report that Sorting Nexin 1 (SNX1) is required for plant salt stress tolerance through affecting endosomal trafficking of SOS1 in Arabidopsis (Arabidopsis thaliana). Disruption of SNX1 caused salt hypersensitivity with increased Na+ accumulation and decreased Na+ efflux in Arabidopsis when challenged with high salinity stress. SNX1 co-localized and interacted with SOS1 in endosomes, promoting its PM localization and protein stability in plants under saline conditions. SOS1 overexpression promoted salt tolerance in the wild-type, whereas such effect was greatly compromised in the snx1-2 mutant. Pharmaceutical results showed that SOS1 recycling from the cytosol to the PM was largely blocked while its vacuolar degradation was accelerated in the snx1-2 mutant. Furthermore, salt-induced SOS1 phosphorylation enhanced its interaction and co-localization with SNX1, which is required for SOS1 PM localization in plants. Our study elucidates that SNX1 facilitates SOS1 PM localization and protein accumulation through endosomal trafficking, thereby enhancing salt tolerance in plants.

Advanced plasma hydrogel evaporator for efficient solar-driven saline-alkaline water treatment and agricultural application

Saline-alkaline land significantly impedes social development and urgently requires effective solutions. Solar-driven interfacial evaporation provides a promising green alternative to address this challenge. In this work, a high-efficiency plasma hydrogel evaporator (PHE) was crosslinked by liquid phase pulsed discharge plasma (LPDP) technology within 10 min, followed by a simple freeze–thaw process. The PHE demonstrates remarkable performance in treating saline-alkaline water. Under one solar irradiation, the PHE achieved an evaporation rate of 2.68 kg·m−2·h−1 in saline-alkaline water with high salinity stress (150 mmol·L−1, Na+ concentration). The collected purified water (PW) showed a reduction in total dissolved solids by three orders of magnitude and a significant elimination of alkalinity. To further evaluate the feasibility of utilizing saline-alkaline water resources with the PHE technology, PW was used for maize cultivation, demonstrating a favorable growth trend. Additionally, PHE effectively addressed the limitations of complex fabrication processes and high evaporation enthalpy associated with traditional evaporators. The work offers a cost-effective and promising approach for freshwater shortages, soil salinization, and saline-alkaline water treatment in challenging environments, contributing to sustainable agricultural development.

Comparative Performance of Ionic and Agro-Physiological Traits for Detecting Salt Tolerance in Wheat Genotypes Grown in Real Field Conditions.

Studying the physiological mechanisms underlying the traits associated with salt tolerance in genotypes could lead to the discovery of new genetic resources for salt tolerance. In this study, the mechanisms of salt tolerance were evaluated, based on ionic, physiological, and agronomic traits in four varieties that differ in their salt tolerance and in 18 F8 recombinant inbred lines (RILs) grown in real field conditions. The salt tolerance of plant materials was assessed under both normal (3.5 mM NaCl) and high salinity stress (150 mM NaCl) conditions for two consecutive years. Different growth and physiological traits were assessed 75 days after sowing, while ion contents in the shoots, grain yield, and its components were determined at the maturity stage. Multivariate analysis was used to conduct a comprehensive evaluation of salt tolerance across various genotypes and traits. The ANOVA results showed significant differences (p ≤ 0.05 and 0.001) among salinity, genotypes, and their interactions for all ionic and agro-physiological traits, with a few exceptions. Salinity stress resulted in a considerable increase in Na+ content and canopy temperature (CT), with a simultaneous decrease of 11.3% to 94.5% in other ionic and agro-physiological traits compared to the control treatment. However, the salt-tolerant genotypes showed minimal increases in Na+ content and CT, as well as decreases in other ionic and agro-physiological traits when compared to salt-sensitive genotypes under salinity stress. All ionic and agro-physiological traits exhibited strong correlations with each other under salinity stress, but these correlations were weak or insignificant under control conditions. The principal component analysis identified Na+ and CT as negative indicators and other ionic and agro-physiological traits as positive indicators for salt tolerance under salinity stress. The negative indicators were strongly linked to salt-sensitive genotypes, while the positive indicators were closely associated with salt-tolerant genotypes. Heatmap clustering, using multiple traits, successfully differentiated the salt-tolerant genotypes from the salt-sensitive ones. The salt-tolerant group showed a significant reduction in Na+ content by 36.9%, in CT by 10.0%, and in HI by 16.7%, along with an increase of 6.3-51.4% in other ionic and agro-physiological traits compared to the salt-sensitive group. In conclusion, the mechanisms associated with Na+ exclusion and high K+/Na+ and Ca2+/Na+ ratios, as well as chlorophyll and relative water content, along with low CT, resulted in significant improvements in growth and yield under salinity stress conditions. Given that the effectiveness of various ionic and agro-physiological traits in evaluating salt tolerance in wheat has been proven in real field conditions, these traits will play a key role in the development of salt-tolerant wheat genotypes.

Optimization of Sargassum bovianum Extraction Techniques for Germination of Wheat, Canola, and Corn Under Different Salinity Stress

Seaweeds are a cheap, eco-friendly, and rich source of plant growth stimulators that can mitigate the adverse effects of salinity stress. This study examined the impact of Sargassum bovianum extracts obtained through different techniques using pressure, heat, and microwave radiations on the germination and growth of wheat, corn, and canola seeds under varying salinity levels (500, 3500, and 6500 µS cm−1). The findings showed that pressure, microwave, and acidic extraction methods were the most effective in extracting polysaccharides, alginate, and nutrients from S. bovianum. Seaweed extract significantly improved the mean germination time (MGT) and germination index (GI) of wheat under high salinity stress and had a positive effect on wheat plumule length (PL) and germination percentage (GP). However, seaweed extract had no significant impact on canola seeds in salinity stress, except for improved canola PL. The PL and seedling vigor index (SVI) of corn were enhanced in low salinity levels, but most treatments reduced PL and SVI in high salinity. This study suggests that using heat, pressure, and microwave techniques for seaweed extraction results in higher polysaccharides and alginate content, leading to improved germination and plant growth, particularly in wheat and canola. These findings can help growers optimize the germination and growth of these important crops.

New insights into biofouling worsening induced by salinity stress in membrane bioreactor: Response of quorum sensing system and its regulation role

Severe worsening of biofouling under salinity stress remains one of the biggest hinderances to membrane bioreactor (MBR) treating saline wastewaters and other membrane technologies applied in saline conditions e.g. seawater desalination. The underlying influential mechanism of salinity stress on biofouling was firstly investigated from the perspective of quorum sensing (QS); Response of QS to salinity stress and its role in regulating biofouling behavior were clarified. Results showed that high salinity stress (over 20 g/L of NaCl) greatly stimulated QS activity, acyl-homoserine lactones (AHLs) were increased by over 200 % and 300 % in mixed liquor and cake layer, respectively; C4-OXO-HSL, C8-OXO-HSL, C10-OXO-HSL and C12-OXO-HSL became the dominant AHLs and showed strong correlations (R2＞0.95) with changes of fouling tendency and extracellular polymeric substances (EPS) characteristics. Metagenomic sequencing further revealed that balance between QS and quorum quenching (QQ) was broken when salinity was over 20 g/L; QS related bacteria and genes were significantly enriched, meanwhile QQ related bacteria and genes were radically suppressed. QS enhancing (by exogenous AHLs) and suppressing experiments (by vanillin) collectively verified the critical regulation role that QS played in biofouling worsening under high salinity stress (mainly via altering EPS characteristics); More importantly, it was demonstrated that suppressing the highly activated QS under high salinity stress was a feasible way to curb the worsening of biofouling. Present study provided new insights into biofouling worsening induced by high salinity stress in MBR; Also, the findings could help to understand biofouling phenomenon in other membrane processes facing salinity stress.

Unveiling significant roles of phytohormone 6-benzylaminopurine in empowering Phaeodactylum tricornutum for high-salinity wastewater treatment and bioresource recovery

High-salinity presents significant challenges in microalgal wastewater treatment and bioresource recovery due to salinity stress. This study explored the use of salt-tolerant microalgae in conjunction with phytohormone regulation. 1 µM 6-benzylaminopurine increased the biomass of Phaeodactylum tricornutum by 38.3 % and enhanced lipid production by 36.8 %. 6-benzylaminopurine significantly improved the removal of inorganic carbon, total nitrogen, and total phosphorus by 85.2 %, 27.4 %, and 31.9 %. Specifically, 6-benzylaminopurine improved K+ transportation by 71.0 %, increased the activity of Ca2+ transport ATPase and Ca2+ sensors by 49.0 %–83.0 %, optimized osmotic balance, and alleviated salt-induced damage. The contents of proline and extracellular polymers increased by 34.8 % and 35.5 %. A 38.4 % reduction in reactive oxygen species indicated that high-salinity stress was mitigated. The analysis of Sustainable Development Goals showed a 56.2 % improvement in Affordable and Clean Energy. Overall, these findings further highlighted the promising application of the phytohormone 6-benzylaminopurine in microalgal high-salinity wastewater treatment and lipid production.

Employing Titanium Dioxide Nanoparticles as Biostimulant against Salinity: Improving Antioxidative Defense and Reactive Oxygen Species Balancing in Eggplant Seedlings.

Salinity is a major abiotic stress that affects the agricultural sector and poses a significant threat to sustainable crop production. Nanoparticles (NPs) act as biostimulants and significantly mitigate abiotic stress. In this context, this experiment was designed to assess the effects of foliar application of titanium dioxide (TiO2) nanoparticles at 200 and 400 ppm on the growth of eggplant (Solanum melongena) seedlings under moderate (75 mM) and high (150 mM) salinity stress. The TiO2-NPs employed were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), and scanning electron microscopy (SEM) analysis. The seedlings were assessed physiologically, growth-wise, and biochemically. The seedlings were significantly affected by their physiological attributes (Fv'/Fm', Fv/Fm, NPQ), growth (root length, shoot length, number of leaves, fresh biomass, dry biomass, leaf greenness), antioxidative enzymes (SOD, POD, CAT, APx, GR), stress indicators (H2O2, MDA), and toxic ion (Na+) concentrations. The maximum decrease in physiological and growth attributes in eggplant seedling leaves was observed with no TiO2-NP application at 150 mM NaCl. Applying TiO2-NPs at 200 ppm showed significantly less decrease in Fv'/Fm', root length, shoot length, number of leaves, fresh biomass, dry biomass, and leaf greenness. In contrast, there were larger increases in SOD, POD, CAT, APx, GR, and TSP. This led to less accumulation of H2O2, MDA, and Na+. No significant difference was observed in higher concentrations of TiO2-NPs compared to the control. Therefore, TiO2-NPs at 200 ppm might be used to grow eggplant seedlings at moderate and high salinity.

Effects of Plant Growth Promoting Halotolerant Pseudomonas Aeruginosa JCM 5962 with Hydrocarbon Degradation Ability, Isolated from Sundarbans Mangrove Area in West Bengal, on Abelmoschus esculentus (Okra) Plant Growth

Plant growth promoting rhizobacteria (PGPR) play a key role in sustainable agricultural practices leading to increased crop productivity. Moreover, PGPR with ability to diminish abiotic stresses like salinity and hydrocarbon contamination in soil, can be developed into potent biofertilizers with maximum ecological benefits. Sundarbans mangrove region in West Bengal, a natural reservoir of diverse microbiota is an important source of PGPR adapted to high salinity and other abiotic stresses like hydrocarbon contamination due to oil spillage and water transport systems, rendering the soil unsuitable for farming. In the present study, a potent PGPR has been isolated from rhizospheric soil of Matla riverbed in mangrove areas of Sundarbans, with simultaneous nitrogen fixing, phosphate solubilizing and plant hormone like indole acetic acid (IAA) producing properties as well as high salt tolerance and hydrocarbon bioremediation abilities. The strain has been identified as Pseudomonas aeruginosa JCM 5962 (NCBI Accession number MK544832.1) on the basis of 16S rRNA analysis. The isolated Pseudomonas aeruginosa strain showed atmospheric nitrogen fixation (3612 ± 2 mg N/ Kg of soil), highest phosphate solubilization index of 3.0 ± 0.06 and 37.14 µg/mL of IAA production. This potent strain also showed salt tolerance upto 7% in culture broth and an uptake of 18.72% of salt. Highest hydrocarbon degradation was shown by this strain in presence of diesel as the sole carbon source. The isolated Pseudomonas aeruginosa strain showed overall improvement in growth of Abelmoschus esculentus (Okra) plants in pot experiments in different conditions like absence of any abiotic stress, presence of 5% salt stress and presence of 1% diesel contaminant. These results indicate that Pseudomonas aeruginosa JCM 5962 can be developed as a potent biofertilizer to be used in agricultural lands of Sundarbans mangrove regions and other areas which are plagued by high salinity and increasing hydrocarbons, particularly petroleum contamination.

Overexpression of dehydroascorbate reductase gene IbDHAR1 improves the tolerance to abiotic stress in sweet potato.

Dehydroascorbate reductase (DHAR), an indispensable enzyme in the production of ascorbic acid (AsA) in plants, is vital for plant tolerance to various stresses. However, there is limited research on the stress tolerance functions of DHAR genes in sweet potato (Ipomoea batatas [L.] Lam). In this study, the full-length IbDHAR1 gene was cloned from the leaves of sweet potato cultivar Xu 18. The IbDHAR1 protein is speculated to be located in both the cytoplasm and the nucleus. As revealed by qRT-PCR, the relative expression level of IbDHAR1 in the proximal storage roots was much greater than in the other tissues, and could be upregulated by high-temperature, salinity, drought, and abscisic acid (ABA) stress. The results of pot experiments indicated that under high salinity and drought stress conditions, transgenic Arabidopsis and sweet potato plants exhibited decreases in H2O2 and MDA levels. Conversely, the levels of antioxidant enzymes APX, SOD, POD, and ACT, and the content of DHAR increased. Additionally, the ratio of AsA/DHA was greater in transgenic lines than in the wild type. The results showed that overexpression of IbDHAR1 intensified the ascorbic acid-glutathione cycle (AsA-GSH) and promoted the activity of the related antioxidant enzyme systems to improve plant stress tolerance and productivity.

Metabolic pathway engineering of high-salinity-induced overproduction of L-proline improves high-salinity stress tolerance of an ectoine-deficient Halomonas elongata.

Halophilic bacteria have adapted to survive in high-salinity environments by accumulating amino acids and their derivatives as organic osmolytes. L-Proline (Pro) is one such osmolyte that is also being used as a feed stimulant in the aquaculture industry. Halomonas elongata OUT30018 is a moderately halophilic bacterium that accumulates ectoine (Ect), but not Pro, as an osmolyte. Due to its ability to utilize diverse biomass-derived carbon and nitrogen sources for growth, H. elongata OUT30018 is used in this work to create a strain that overproduces Pro, which could be used as a sustainable Pro-rich feed additive. To achieve this, we replaced the coding region of H. elongata OUT30018's Ect biosynthetic operon with the artificial self-cloned proBm1AC gene cluster that encodes the Pro biosynthetic enzymes: feedback-inhibition insensitive mutant γ-glutamate kinase (γ-GKD118N/D119N), γ-glutamyl phosphate reductase, and pyrroline-5-carboxylate reductase. Additionally, the putA gene, which encodes the key enzyme of Pro catabolism, was deleted from the genome to generate H. elongata HN6. While the Ect-deficient H. elongata KA1 could not grow in minimal media containing more than 4% NaCl, H. elongata HN6 thrived in the medium containing 8% NaCl by accumulating Pro in the cell instead of Ect, reaching a concentration of 353.1 ± 40.5 µmol/g cell fresh weight, comparable to the Ect accumulated in H. elongata OUT30018 in response to salt stress. With its genetic background, H. elongata HN6 has the potential to be developed into a Pro-rich cell factory for upcycling biomass waste into single-cell feed additives, contributing to a more sustainable aquaculture industry.IMPORTANCEWe report here the evidence for de novo biosynthesis of Pro to be used as a major osmolyte in an ectoine-deficient Halomonas elongata. Remarkably, the concentration of Pro accumulated in H. elongata HN6 (∆ectABC::mCherry-proBm1AC ∆putA) is comparable to that of ectoine accumulated in H. elongata OUT30018 in response to high-salinity stress. We also found that among the two γ-glutamate kinase mutants (γ-GKD118N/D119N and γ-GKD154A/E155A) designed to resemble the two known Escherichia coli feedback-inhibition insensitive γ-GKD107N and γ-GKE143A, the γ-GKD118N/D119N mutant is the only one that became insensitive to feedback inhibition by Pro in H. elongata. As Pro is one of the essential feed additives for the poultry and aquaculture industries, the genetic makeup of the engineered H. elongata HN6 would allow for the sustainable upcycling of high-salinity waste biomass into a Pro-rich single-cell eco-feed.

Interactive effects of temperature and salinity on metabolism and activity of the copepod Tigriopus californicus.

In natural environments, two or more abiotic parameters often vary simultaneously, and interactions between co-varying parameters frequently result in unpredictable, non-additive biological responses. To better understand the mechanisms and consequences of interactions between multiple stressors, it is important to study their effects on not only fitness (survival and reproduction) but also performance and intermediary physiological processes. The splash-pool copepod Tigriopus californicus tolerates extremely variable abiotic conditions and exhibits a non-additive, antagonistic interaction resulting in higher survival when simultaneously exposed to high salinity and acute heat stress. Here, we investigated the response of T. californicus in activity and oxygen consumption under simultaneous manipulation of salinity and temperature to identify whether this interaction also arises in these sublethal measures of performance. Oxygen consumption and activity rates decreased with increasing assay salinity. Oxygen consumption also sharply increased in response to acute transfer to lower salinities, an effect that was absent upon transfer to higher salinities. Elevated temperature led to reduced rates of activity overall, resulting in no discernible impact of increased temperature on routine metabolic rates. This suggests that swimming activity has a non-negligible effect on the metabolic rates of copepods and must be accounted for in metabolic studies. Temperature also interacted with assay salinity to affect activity, and with acclimation salinity to affect routine metabolic rates upon acute salinity transfer, implying that the sublethal impacts of these co-varying factors are also not predictable from experiments that study them in isolation.

Enhanced accumulation of γ-aminobutyric acid by deletion of aminotransferase genes involved in γ-aminobutyric acid catabolism in engineered Halomonas elongata.

In this study, we were able to increase the yield of GABA by 1.5 times in the GABA-producing H. elongata ZN3 strain by deleting the gabT gene, which encodes GABA-AT, the initial enzyme of the GABA catabolic pathway. We also report the first in vivo evidence for GABA aminotransferase activity of an ectB-encoded DABA-AT, confirming a longstanding speculation based on the reported in vitro GABA-AT activity of DABA-AT. According to our findings, the DABA-AT enzyme can catalyze the initial step of GABA catabolism, in addition to its known function in ectoine biosynthesis. This creates a cycle that promotes adequate substrate flow between the two pathways, particularly during the early stages of high-salinity stress response when the expression of the ectB gene is upregulated.

Effects of Prolonged High Salinity Stress on Alfalfa (Medicago sativa L.) Cultivars and Populations

Background: Alfalfa is a promising crop for improving soil structure and restoring agricultural land, particularly in areas affected by salinity. However, high and continuing salinity in soil and irrigation water can pose a significant challenge to the growth and productivity of alfalfa. The objective of this study was to investigate the effects of prolonged high salinity stress on alfalfa cultivars and populations. Methods: The material used in this study included 16 alfalfa populations and four alfalfa cultivars that exhibit salt tolerance during germination and early seedling development. The materials were exposed to 17.52 dS m-1 saline irrigation water stress for three months. As well as the morphology, survival at three months and crude ash, sodium and chloride ions were measured. Result: Salt-tolerant plants showed a slowdown in growth compared to control conditions, although they were still able to maintain growth. Duration and severity of stress affected the salt tolerance of the genotypes. The survival rates of the materials remained relatively unchanged for the first two months, but decreased significantly by the end of the third month. Furthermore, the survival rate of the materials increased as the amount of sodium and chloride ions absorbed by the plant decreased under high salinity conditions. Genetic material demonstrating long-term high salinity tolerance is crucial for resistance breeding and holds promise for the development of tolerant cultivars that can be grown under field conditions in the future. The properties of this material need to be determined and its long-term performance in field conditions needs to be tested.