Cardiorespiratory fitness in breast cancer survivors

Synergistic effect of Pseudomonas putida and endomycorrhizal inoculation on the physiological response of onion (Allium cepa L.) to saline conditions

Salinity stress negatively affects the growth and yield of crops worldwide. Onion (Allium cepa L.) is moderately sensitive to salinity. Beneficial microorganisms can potentially confer salinity tolerance. This study investigated the effects of endomycorrhizal fungi (M), Pseudomonas putida (Ps) and their combination (MPs) on onion growth under control (0 ppm), moderate (2000 ppm) and high (4000 ppm) NaCl salinity levels. A pot experiment was conducted with sandy loam soil and onion cultivar Giza 20. Results showed that salinity reduced growth attributes, leaf pigments, biomass and bulb yield while increasing oxidative stress markers. However, individual or combined inoculations significantly increased plant height, bulb diameter and biomass production compared to uninoculated plants under saline conditions. MPs treatment provided the highest stimulation, followed by Pseudomonas and mycorrhizae alone. Overall, dual microbial inoculation showed synergistic interaction, conferring maximum benefits for onion growth, bulbing through integrated physiological and biochemical processes under salinity. Bulb yield showed 3.5, 36 and 83% increase over control at 0, 2000 and 4000 ppm salinity, respectively. In conclusion, combined application of mycorrhizal-Pseudomonas inoculations (MPs) effectively mitigate salinity stress. This approach serves as a promising biotechnology for ensuring sustainable onion productivity under saline conditions.

NaCl Modifies Biochemical Traits in Bacterial Endophytes Isolated from Halophytes: Towards Salinity Stress Mitigation Using Consortia

Bacterial endophytes (120) were isolated from six halophytes (Distichlis spicata, Cynodon dactylon, Eragrostis obtusiflora, Suaeda torreyana, Kochia scoparia, and Baccharis salicifolia). These halophiles were molecularly identified and characterized with or without NaCl conditions. Characterization was based on tests such as indole acetic acid (IAA), exopolysaccharides (EPS), and siderophores (SID) production; solubilization of phosphate (P), potassium (K), zinc (Zn), and manganese (Mn); mineralization of phytate; enzymatic activity (acid and alkaline phosphatase, phytases, xylanases, and chitinases) and the mineralization/solubilization mechanisms involved (organic acids and sugars). Moreover, compatibility among bacteria was assessed. Eleven halophiles were characterized as highly tolerant to NaCl (2.5 M). The bacteria isolated were all different from each other. Two belonged to Bacillus velezensis and one to B. pumilus while the rest of bacteria were identified up to the genus level as belonging to Bacillus, Halobacillus, Halomonas, Pseudomonas, Nesterenkonia, and three strains of Oceanobacillus. The biochemical responses of nutrient solubilization and enzymatic activity were different between bacteria and were influenced by the presence of NaCl. Organic acids were involved in P mineralization and nutrient solubilization. Tartaric acid was common in the solubilization of P, Zn, and K. Maleic and vanillic acid were only detected in Zn and K solubilization, respectively. Furthermore, sugars appeared to be involved in the solubilization of nutrients; fructose was detected in the solubilization tests. Therefore, these biochemical bacterial characteristics should be corroborated in vivo and tested as a consortium to mitigate saline stress in glycophytes under a global climate change scheme that threatens to exacerbate soil salinity.

Improving crop salt tolerance through soil legacy effects

Soil salinization poses a critical problem, adversely affecting plant development and sustainable agriculture. Plants can produce soil legacy effects through interactions with the soil environments. Salt tolerance of plants in saline soils is not only determined by their own stress tolerance but is also closely related to soil legacy effects. Creating positive soil legacy effects for crops, thereby alleviating crop salt stress, presents a new perspective for improving soil conditions and increasing productivity in saline farmlands. Firstly, the formation and role of soil legacy effects in natural ecosystems are summarized. Then, the processes by which plants and soil microbial assistance respond to salt stress are outlined, as well as the potential soil legacy effects they may produce. Using this as a foundation, proposed the application of salt tolerance mechanisms related to soil legacy effects in natural ecosystems to saline farmlands production. One aspect involves leveraging the soil legacy effects created by plants to cope with salt stress, including the direct use of halophytes and salt-tolerant crops and the design of cropping patterns with the specific crop functional groups. Another aspect focuses on the utilization of soil legacy effects created synergistically by soil microorganisms. This includes the inoculation of specific strains, functional microbiota, entire soil which legacy with beneficial microorganisms and tolerant substances, as well as the application of novel technologies such as direct use of rhizosphere secretions or microbial transmission mechanisms. These approaches capitalize on the characteristics of beneficial microorganisms to help crops against salinity. Consequently, we concluded that by the screening suitable salt-tolerant crops, the development rational cropping patterns, and the inoculation of safe functional soils, positive soil legacy effects could be created to enhance crop salt tolerance. It could also improve the practical significance of soil legacy effects in the application of saline farmlands.

Halophytic Bacterial Endophyte Microbiome from Coastal Desert-Adapted Wild Poaceae Alleviates Salinity Stress in the Common Wheat Triticum aestivum L

Abiotic stresses threaten the strategic crops of Poaceae (Gramineae) worldwide. Habitat-adapted microbiome of wild plants has the potential to alleviate abiotic stresses in alternate hosts. Persian Gulf's coastal deserts are colonized by halophyte plants hosting habitat-adapted halophytic microbiota. Here, endophytic bacteria from wild Poaceae in coastal deserts of the north Persian Gulf at Hormozgan province, Iran, were isolated and screened for mitigating salinity stress in wheat. Accordingly, seven dominant species of wild Poaceae in the region, i.e., Aeloropus lagopoides, Aeloropus litiralis, Chrysopogon aucheri, Cymbopogon olivieri, Desmostachya sp., Halopayrum mucronatum, and Sporbuls arabicus, were explored. In total, 367 endophytic bacteria were isolated, 90 of which tolerated 2.5-M NaCl. Of these, 38 strains were selected based on their bioactivity and applied for in vitro wheat-interaction assays under 250-mM NaCl stress. Five superior strains promoted seed germination and growth indices in rain-fed winter wheat cv. Sardari, i.e., Bacillus subtilis B14, B19, & B27, Bacillus sp. B21, and Bacillus licheniformis Ba38. In planta assays in saline soil (2.7 dS m-1) using the superior strains indicated that Bacillus sp. B21 and Bacillus licheniformis Ba38 increased germination and root and shoot lengths and their dry and fresh weights in wheat seedlings. Moreover, phenolics and flavonoids contents of wheat seedlings were influenced by endophyte application. Thus, the coastal desert-adapted microbiome of wild Poaceae could alleviate abiotic stress and promote growth in cultivated species of Poaceae, such as wheat.

Isolation and identification of a new Bacillus glycinifermentans strain from date palm rhizosphere and its effect on barley seeds under heavy metal stress

Soil contamination by heavy metals is one of the major problems that adversely decrease plant growth and biomass production. Inoculation with the plant growth-promoting rhizobacteria (PGPR) can attenuate the toxicity of heavy metals and enhancing the plant growth. In this study, we evaluated the potential of a novel extremotolerant strain (IS-2 T) isolated from date palm rhizosphere to improve barley seedling growth under heavy metal stress. The species-level identification was carried out using morphological and biochemical methods combined with whole genome sequencing. The bacterial strain was then used in vitro for inoculating Hordeum vulgare L. exposed to three different Cr, Zn, and Ni concentrations (0.5, 1, and 2 mM) in petri dishes and different morphological parameters were assessed. The strain was identified as Bacillus glycinifermentans species. This strain showed high tolerance to pH (6-11), salt stress (0.2-2 M), and heavy metals. Indeed, the minimum inhibitory concentrations at which bacterium was unable to grow were 4 mM for nickel, 3 mM for zinc, more than 8 mM for copper, and 40 mM for chromium, respectively. It was observed that inoculation of Hordeum vulgare L. under metal stress conditions with Bacillus glycinifermentans IS-2 T stain improved considerably the growth parameters. The capacity of the IS-2 T strain to withstand a range of abiotic stresses and improve barley seedling development under lab conditions makes it a promising candidate for use as a PGPR in zinc, nickel, copper, and chromium bioremediation.

Comparative genomics of seven genomes of genus Idiomarina reveals important halo adaptations and genes for stress response

The genus Idiomarina consists of halophilic and/or haloalkaliphilic organisms. We compared the complete genomes of seven strains of the genus Idiomarina to investigate its adaptation to saline environment. A total of 1,313 core genes related to salinity tolerance, stress response, antibiotic resistance genes, virulence factors, and drug targets were found. Comparative genomics revealed various genes involved in halo adaptations of these organisms, including transporters and influx or efflux systems for elements such as Fe, Cu, Zn, Pb, and Cd. In agreement with their isolation sources (such as hydrothermal vents and marine sediments) and environments abundant in heavy metals, various resistance proteins and transporters associated with metal tolerance were also identified. These included copper resistance proteins, zinc uptake transcriptional repressor Zur, MerC domain-containing protein, Cd(II)/Pb(II)-responsive transcriptional regulator, Co/Zn/Cd efflux system protein, and mercuric transporter. Interestingly, we observed that the carbohydrate metabolism pathways were incomplete in all the strains and transporters used for absorption of small sugars were also not found in them. Also, the presence of higher proportion of genes involved in protein metabolism than carbohydrate metabolism indicates that proteinaceous substrates act as the major food substrates for these bacterial strains than carbohydrates. Genomic islands were detected in some species, highlighting the role of horizontal gene transfer for acquisition in novel genes. Genomic rearrangements in terms of partially palindromic regions were detected in all strains. To our knowledge, this is the first comprehensive comparative genomics study among the genus Idiomarina revealing unique genomic features within bacterial species inhabiting different ecological niches.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03887-3.

Leveraging genomic information to predict environmental preferences of bacteria

Genomic information is now available for a broad diversity of bacteria, including uncultivated taxa. However, we have corresponding knowledge on environmental preferences (i.e. bacterial growth responses across gradients in oxygen, pH, temperature, salinity, and other environmental conditions) for a relatively narrow swath of bacterial diversity. These limits to our understanding of bacterial ecologies constrain our ability to predict how assemblages will shift in response to global change factors, design effective probiotics, or guide cultivation efforts. We need innovative approaches that take advantage of expanding genome databases to accurately infer the environmental preferences of bacteria and validate the accuracy of these inferences. By doing so, we can broaden our quantitative understanding of the environmental preferences of the majority of bacterial taxa that remain uncharacterized. With this perspective, we highlight why it is important to infer environmental preferences from genomic information and discuss the range of potential strategies for doing so. In particular, we highlight concrete examples of how both cultivation-independent and cultivation-dependent approaches can be integrated with genomic data to develop predictive models. We also emphasize the limitations and pitfalls of these approaches and the specific knowledge gaps that need to be addressed to successfully expand our understanding of the environmental preferences of bacteria.

Comprehensive genome analysis of Pseudomonas sp. SWRIQ11, a new plant growth-promoting bacterium that alleviates salinity stress in olive

The study presents the genome analysis of a new Pseudomonas sp. (SWRIQ11), which can alleviate salinity stress effects on growth of olive seedlings in greenhouse study. The strain SWRIQ11 can tolerate salinity up to 6%, produce siderophores, indole acetic acid (IAA), aminocyclopropane-1-carboxylate (ACC) deaminase, and has the phosphate-solubilizing capability. The SWRIQ11 genome contained an assembly size of 6,196,390 bp with a GC content of 60.1%. According to derived indices based on whole-genome sequences for species delineation, including tetra nucleotide usage patterns (TETRA), genome-to-genome distance (GGDC), and average nucleotide identity (ANI), Pseudomonas sp. SWRIQ11 can be considered a novel species candidate. The phylogenetic analysis revealed SWRIQ11 clusters with Pseudomonas tehranensis SWRI196 in the same clade. The SWRIQ11 genome was rich in genes related to stress sensing, signaling, and response, chaperones, motility, attachments, colonization, and enzymes for degrading plant-derived carbohydrates. Furthermore, the genes for production of exopolysaccharides, osmoprotectants, phytohormones, and ACC deaminase, ion homeostasis, nutrient acquisition, and antioxidant defenses were identified in the SWRIQ11 genome. The results of genome analysis (identification of more than 825 CDSs related to plant growth-promoting and stress-alleviating traits in the SWRIQ11 genome which is more than 15% of its total CDSs) are in accordance with laboratory and greenhouse experiments assigning the Pseudomonas sp. SWRIQ11 as a halotolerant plant growth-promoting bacterium (PGPB). This research highlights the potential safe application of this new PGPB species in agriculture as a potent biofertilizer.

Mechanism of Salt Tolerance and Plant Growth Promotion in Priestia megaterium ZS-3 Revealed by Cellular Metabolism and Whole-Genome Studies

Approximately one-third of agricultural land worldwide is affected by salinity, which limits the productivity and sustainability of crop ecosystems. Plant-growth-promoting rhizobacteria (PGPR) are a potential solution to this problem, as PGPR increases crop yield through improving soil fertility and stress resistance. Previous studies have shown that Priestia megaterium ZS-3(ZS-3) can effectively help plants tolerate salinity stress. However, how ZS-3 regulates its metabolic adaptations in saline environments remains unclear. In this study, we monitored the metabolic rearrangement of compatibilisers in ZS-3 and combined the findings with genomic data to reveal how ZS-3 survives in stressful environments, induces plant growth, and tolerates stress. The results showed that ZS-3 tolerated salinity levels up to 9%. In addition, glutamate and trehalose help ZS-3 adapt to osmotic stress under low NaCl stress, whereas proline, K+, and extracellular polysaccharides regulate the osmotic responses of ZS-3 exposed to high salt stress. Potting experiments showed that applying the ZS-3 strain in saline and neutral soils could effectively increase the activities of soil acid phosphatase, urease, and invertase in both soils, thus improving soil fertility and promoting plant growth. In addition, strain ZS-3-GFP colonised the rhizosphere and leaves of Cinnamomum camphora well, as confirmed by confocal microscopy and resistance plate count analysis. Genomic studies and in vitro experiments have shown that ZS-3 exhibits a variety of beneficial traits, including plant-promoting, antagonistic, and other related traits (such as resistance to saline and heavy metal stress/tolerance, amino acid synthesis and transport, volatile compound synthesis, micronutrient utilisation, and phytohormone biosynthesis/regulatory potential). The results support that ZS-3 can induce plant tolerance to abiotic stresses. These data provide important clues to further reveal the interactions between plants and microbiomes, as well as the mechanisms by which micro-organisms control plant health.

Effectiveness of Phosphate and Zinc Solubilizing Paenarthrobacter nitroguajacolicus P1 as Halotolerant Rhizobacterium with Growth-Promoting Activity on Pistacia vera L

Plant growth-promoting rhizobacteria (PGPR) are beneficial microorganisms to develop microbial fertilizers. Biofertilizers can accelerate plant growth and enhance crop yields. The current research aimed to isolate and identify rhizobacterium with plant growth-promoting activity in the rhizospheric region of pistachio trees in arid and salty region of Iran. In the present study, 26 bacterial isolates were isolated from the rhizospheric region of the pistachio trees. Plant growth-promoting characteristics of isolated bacteria, including the ability to solubilize phosphate and zinc, produce hydrolyzing enzymes, and hydrogen cyanide (HCN), as well as synthesize indole-3-acetic acid (IAA) were evaluated through in vitro assays. Based on these activities, five multifunctional bacterial strains designated P1, P10, P11, P17, and P19 were then applied and their effect was studied on the growth and physiological properties of Pistacia vera L. seedlings by pot experiments under normal conditions. Finally, the most efficient strain has been identified by analysis of the 16S rRNA gene sequence. According to the results, all the isolated bacteria exhibited considerable plant growth-promoting properties. They could produce amylase (n = 26, 2 ± 0.00-13 ± 0.42 mm), lipase (n = 24, 2 ± 0.00-9 ± 0.23 mm), protease (n = 20, 1 ± 0.00-17 ± 0.0 mm), indole-3-acetic acid (n = 26, ranging from 5.05 ± 0.08 to 11.5 ± 0.11 μg/mL) and HCN (n = 24). Six isolates showed significant growth at 20% w/v NaCl. Inoculation of P1, P17, and P19 increased chlorophyll, carotenoid, and phenolic content in treated Pistacia vera L. seedlings. P1 and P11 inoculated plants showed an enhanced level of anthocyanin and proline. These most effective strains were catalase and Gram-positive bacterium and showed antibiotic sensitivity. They can consider as halotolerant PGPR, due to the growth in the presence of NaCl (20% w/v). Finally, P1 inoculated plants exhibited higher levels of sugar content. This strain showed the most similarity (99.92%-1322 bp) to Paenarthrobacter nitroguajacolicus based on 16S rRNA gene sequence. Based on the results, Paenarthrobacter nitroguajacolicus P1 with multiple PGPR can be applied as a promising candidate in the soil-Pistacia vera L. system to improve their productivity and health by increasing available nutrient content, improving photosynthetic parameters, and producing phytohormones and HCN.

Larger presence of ectomycorrhizae detected from pygmy pine ecotype in the fire-frequent pine barrens ecosystem

Pine barrens ecosystem has acidic, sandy, and nutrient-poor soil and is prone to drought and fire. In the New Jersey Pine Barrens, the predominant pitch pine (Pinus rigida) consists of two ecotypes: the regular pitch pines with heights of 4.6-12 m, and the pygmy pines of low stature (1.2-1.8 m) in the New Jersey Pine Plains. Previous ecological studies suggested that the dwarf pines in the Pine Plains that are embedded within the Pine Barrens were an evolutionary adaptation to frequent fire. Pines are obligate ectomycorrhizal (EcM) mutualists, and their root mycobiota may contribute to stress protection and plant health. However, information on the mycobiota associated with plants in the pine barrens ecosystem is lacking. To have a holistic understanding of the evolution and adaptation in this stressed environment, we used both culture-independent metabarcoding and culture-based method to characterize the mycobiota from soil and root of the two ecotypes and to identify core mycobiota. We found that Agaricomycetes, Leotiomycetes, and Mucoromycotina are predominant fungi in the New Jersey Pine Barrens ecosystem, which is rich in root mutualistic fungi. We observed that the pygmy pine roots had significantly higher density of EcM tips than the regular pine roots. This was corroborated by our metabarcoding analysis, which showed that the pygmy pine trees had higher ratio of ectomycorrhiza-forming fungi than the regular-statured pines. We hypothesize that symbiotrophic EcM fungi associated with pygmy pines are capable of mitigating high fire stress in the Pine Plains.

Enhanced Physiological and Biochemical Performance of Mung Bean and Maize under Saline and Heavy Metal Stress through Application of Endophytic Fungal Strain SL3 and Exogenous IAA

Modern irrigation practices and industrial pollution can contribute to the simultaneous occurrence of salinity and heavy metal contamination in large areas of the world, resulting in significant negative effects on crop productivity and sustainability. This study aimed to investigate the growth-promoting potentials of an important endophytic fungal strain SL3 and to compare its potential with exogenous IAA (indole-3-acetic acid) in the context of salt and heavy metal stress. The strain was assessed for plant growth-promoting traits such as the production of indole-3-acetic acid, gibberellins (GA), and siderophore. We selected two important crops, mung bean and maize, and examined various physiological and biochemical characteristics under 300 mM NaCl and 2.5 mM Pb stress conditions, with and without the application of IAA and SL3. This study's results demonstrated that both IAA and SL3 positively impacted the growth and development of plants under normal and stressed conditions. In NaCl and Pb-induced stress conditions, the growth of mung bean and maize plants was significantly reduced. However, the application of IAA and SL3 helped to alleviate stress, leading to a significant increase in shoot/root length and weight compared to IAA and SL3 non-treated plants. The results revealed that photosynthetic pigments, accumulation of catalase (CAT), phenolic contents, polyphenol oxidase, and flavanols are higher in the IAA and SL3-treated plants than in the non-inoculated plants. This study's findings revealed that applying the SL3 fungal strain positively influenced various physiological and biochemical processes in tested plant species under normal and stress conditions of NaCl and Pb. These findings also suggested that SL3 could be a potential replacement for widely used IAA to promote plant growth by improving photosynthetic efficiency, reducing oxidative stress, and enhancing metabolic activities in plants, including mung and maize. Moreover, this study highlights that SL3 has synergistic effects with IAA in enhancing resilience to salt and heavy stress and offers a promising avenue for future agricultural applications in salt and heavy metal-affected regions.

Isolation and characterization of halotolerant plant growth promoting rhizobacteria from mangrove region of Sundarbans, India for enhanced crop productivity

Halotolerant plant growth promoting rhizobacteria (PGPR) are beneficial microorganisms utilized to mitigate the biotic and abiotic stresses in plants. The areas of Sundarban mangroves of West Bengal, India have been reported to be rich in halotolerant microflora, yet major area remains unexplored. The present study, therefore, aims to map down the region-specific native microbial community potent of salt tolerance, plant growth promoting (PGP) activity and antagonistic activity against fungal pathogens. Bacterial samples were isolated from the saline soil of the Sundarban mangroves. A total of 156 bacterial samples were isolated and 20 were screened for their salt tolerance potential. These isolates were characterised using morphological, biochemical, and molecular approaches. Based on 16s rRNA sequencing, they were classified into 4 different genera, including Arthrobacter sp. (01 isolate), Pseudomonas plecoglossicida (01 isolate), Kocuria rosea (01 isolate), and Bacillus (17 isolates). The halotolerant isolates which possessed plant growth promoting traits including phosphate, and zinc solubilization, indole acetic acid production, siderophore, and ammonia generation were selected. Further, the effect of two halotolerant isolates GN-5 and JR-12 which showed most prominent PGP activities was evaluated in pea plant under high salinity conditions. The isolates improved survival by promoting germination (36 to 43%) and root-shoot growth and weight of pea plant in comparison to non-inoculated control plants. In a subsequent dual culture confrontation experiment, both these halo-tolerant isolates showed antagonistic activities against the aggressive root rot disease-causing Macrophomina phaseolina (Tassi) Goid NAIMCC-F-02902. The identified isolates could be used as potential bioagents for saline soils, with potential antagonistic effect on root rot disease. However, further studies at the physiological and molecular level would help to delineate a detail mechanistic understanding of broad-spectrum defence against salinity and potential biotic pathogen.

Temperature-induced modulation of stress-tolerant PGP genes bioprospected from Bacillus sp. IHBT-705 associated with saffron (Crocus sativus) rhizosphere: A natural -treasure trove of microbial biostimulants

There is a renewed interest in sustainable agriculture wherein novel plant growth-promoting rhizobacteria (PGPR) are being explored for developing efficient biostimulants. The key requirement of a microbe to qualify as a good candidate for developing a biostimulant is its intrinsic plant growth-promoting (PGP) characteristics. Though numerous studies have been conducted to assess the beneficial effects of PGPRs on plant growth under normal and stressed conditions but not much information is available on the characterization of intrinsic traits of PGPR under stress. Here, we focused on understanding how temperature stress impacts the functionality of key stress tolerant and PGP genes of Bacillus sp. IHBT-705 isolated from the rhizosphere of saffron (Crocus sativus). To undertake the study, Bacillus sp. IHBT-705 was grown under varied temperature regimes, their PGP traits were assessed from very low to very high-temperature range and the expression trend of targeted stress tolerant and PGP genes were analyzed. The results illustrated that Bacillus sp. IHBT-705 is a stress-tolerant PGPR as it survived and multiplied in temperatures ranging from 4°C-50°C, tolerated a wide pH range (5-11), withstood high salinity (8%) and osmolarity (10% PEG). The PGP traits varied under different temperature regimes indicating that temperature influences the functionality of PGP genes. This was further ascertained through whole genome sequencing followed by gene expression analyses wherein certain genes like cspB, cspD, hslO, grpE, rimM, trpA, trpC, trpE, fhuC, fhuD, acrB5 were found to be temperature sensitive while, cold tolerant (nhaX and cspC), heat tolerant (htpX) phosphate solubilization (pstB1), siderophore production (fhuB and fhuG), and root colonization (xerC1 and xerC2) were found to be highly versatile as they could express well both under low and high temperatures. Further, the biostimulant potential was checked through a pot study on rice (Oryza sativa), wherein the application of Bacillus sp. IHBT-705 improved the length of shoots, roots, and number of roots over control. Based on the genetic makeup, stress tolerance potential, retention of PGP traits under stress, and growth-promoting potential, Bacillus sp. IHBT-705 could be considered a good candidate for developing biostimulants.

Biomining Sesuvium portulacastrum for halotolerant PGPR and endophytes for promotion of salt tolerance in Vigna mungo L

Halophytic plants can tolerate a high level of salinity through several morphological and physiological adaptations along with the presence of salt tolerant rhizo-microbiome. These microbes release phytohormones which aid in alleviating salinity stress and improve nutrient availability. The isolation and identification of such halophilic PGPRs can be useful in developing bio-inoculants for improving the salt tolerance and productivity of non-halophytic plants under saline conditions. In this study, salt-tolerant bacteria with multiple plant growth promoting characteristics were isolated from the rhizosphere of a predominant halophyte, Sesuvium portulacastrum grown in the coastal and paper mill effluent irrigated soils. Among the isolates, nine halotolerant rhizobacterial strains that were able to grow profusely at a salinity level of 5% NaCl were screened. These isolates were found to have multiple plant growth promoting (PGP) traits, especially 1-aminocyclopropane-1-carboxylic acid deaminase activity (0.32-1.18  μM of α-ketobutyrate released mg^-1 of protein h^-1) and indole acetic acid (9.4-22.8  μg mL^-1). The halotolerant PGPR inoculation had the potential to improve salt tolerance in Vigna mungo L. which was reflected in significantly (p < 0.05) higher germination percentage (89%) compared to un-inoculated seeds (65%) under 2% NaCl. Similarly, shoot length (8.9-14.6 cm) and vigor index (792-1785) were also higher in inoculated seeds. The strains compatible with each other were used for the preparation of two bioformulations and these microbial consortia were tested for their efficacy in salt stress alleviation of Vigna mungo L. under pot study. The inoculation improved the photosynthetic rate (12%), chlorophyll content (22%), shoot length (5.7%) and grain yield (33%) in Vigna mungo L. The enzymatic activity of catalase and superoxide dismutase were found to be lower (7.0 and 1.5%, respectively) in inoculated plants. These results revealed that halotolerant PGPR isolated from S. portulacastrum can be a cost-effective and ecologically sustainable method to improve crop productivity under high saline conditions.

Development of rapid and precise approach for quantification of bacterial taxa correlated with soil health

The structure and dynamic of soil bacterial community play a crucial role in soil health and plant productivity. However, there is a gap in studying the un-/or reclaimed soil bacteriome and its impact on future plant performance. The 16S metagenomic analysis is expensive and utilize sophisticated pipelines, making it unfavorable for researchers. Here, we aim to perform (1) in silico and in vitro validation of taxon-specific qPCR primer-panel in the detection of the beneficial soil bacterial community, to ensure its specificity and precision, and (2) multidimensional analysis of three soils/locations in Egypt ('Q', 'B', and 'G' soils) in terms of their physicochemical properties, bacteriome composition, and wheat productivity as a model crop. The in silico results disclosed that almost all tested primers showed high specificity and precision toward the target taxa. Among 17 measured soil properties, the electrical conductivity (EC) value (up to 5 dS/m) of 'Q' soil provided an efficient indicator for soil health among the tested soils. The 16S NGS analysis showed that the soil bacteriome significantly drives future plant performance, especially the abundance of Proteobacteria and Actinobacteria as key indicators. The functional prediction analysis results disclosed a high percentage of N-fixing bacterial taxa in 'Q' soil compared to other soils, which reflects their positive impact on wheat productivity. The taxon-specific qPCR primer-panel results revealed a precise quantification of the targeted taxa compared to the 16S NGS analysis. Moreover, 12 agro-morphological parameters were determined for grown wheat plants, and their results showed a high yield in the 'Q' soil compared to other soils; this could be attributed to the increased abundance of Proteobacteria and Actinobacteria, high enrichment in nutrients (N and K), or increased EC/nutrient availability. Ultimately, the potential use of a taxon-specific qPCR primer-panel as an alternative approach to NGS provides a cheaper, user-friendly setup with high accuracy.

Identification of endophytic fungi with ACC deaminase-producing isolated from halophyte Kosteletzkya Virginica

Seashore mallow (Kosteletzkya virginica), as a noninvasive perennial halophytic oilseed-producing dicot, is native from the Gulf to the Atlantic coasts of the U.S. The purpose of our research was to investigate 1-aminocyclopropane-1carboxylic acid deaminase (ACCD) producing endophytic fungi from K.virginica. A total of 59 endophytic fungal strains, isolated from roots in K.virginica of seedlings, were grouped into 12 genera including in Penicillium, Aspergillus, Fusarium, Trichoderma, Rhizopycnis sp., Ceriporia Donk, Trametes sp., Schizophyllum commune sp., Alternaria, Cladosporium, Cylindrocarpon, and Scytalidium according to sequences of ITS. The ACD activity of 10 endophytic fungi isolated was detected. T.asperellum had the highest ACC deaminase activity among all 10 isolated genera of fungal strains, followed by T. viride. Dry weight and fresh weight of plant, plant height, root length, SOD activity, and chlorophyll content of wheat and soybean inoculated with T.asperellum or T. viride was increased compared with non-inoculated control plants under non salt or salt stress. Further analysis showed that T.asperellum or T.viride strains induced downregulation of the expression of ethylene synthesis-related genes such as ACC oxidase (ACO) and ACC synthase (ACS), thereby reducing ethylene synthesis and damage to plants under salt stress. These endophytic fungi can be used as alternative bioinoculants to increase crop yield in saline soil.

Potential of halotolerant PGPRs in growth and yield augmentation of Triticum aestivum var. HD2687 and Zea mays var. PSCL4642 cultivars under saline conditions

This study aimed to culture and screen salt-tolerant Plant growth promoting rhizobacteria (PGPRs) from Bougainvillea glabra rhizosphere to improve wheat HD-2687 and maize PSCL-4642 cultivars under saline conditions up to the seedling stage. Twenty-four rhizobacterial isolates were screened for salt tolerance at different NaCl levels. Indole acetic acid (IAA) production, phosphate solubilization, and siderophore and hydrogen cyanide (HCN) production of salinity-tolerant isolates were tested. Positive salt-tolerant PGPRs were further subjected to seedling studies to examine the improvement in the development of experimental crops under 50, 100, 150, and 200 mM NaCl concentrations with/without bacterial inoculant. Of the 24 isolates, BoGl123 was the most promising PGPR, which showed the maximum phosphate solubilization, and IAA, siderophore and HCN production. It was further subjected to seedling studies. In comparison with controls, BoGl123 resulted in a higher radicle length in maize (34 mm, 87.4%) and wheat (26.8 mm, 85.8%) at the 50 mM salinity level. At the 100 mM NaCl level, the radicle length of wheat and maize seedlings was increased by 82.5% and 78.6%, respectively, compared with controls. At different NaCl concentrations, BoGl123 improved the plumule length of seedlings in both crops. The stress tolerance attributes and plant growth promotion (PGP) indicate the potential of Pseudomonas fluorescens BoGl123 to be used as a microbial inoculant in the cultivation of wheat and maize under stressful conditions.

Bacillus spp. as Bioagents: Uses and Application for Sustainable Agriculture

Food security will be a substantial issue in the near future due to the expeditiously growing global population. The current trend in the agriculture industry entails the extravagant use of synthesized pesticides and fertilizers, making sustainability a difficult challenge. Land degradation, lower production, and vulnerability to both abiotic and biotic stresses are problems caused by the usage of these pesticides and fertilizers. The major goal of sustainable agriculture is to ameliorate productivity and reduce pests and disease prevalence to such a degree that prevents large-scale damage to crops. Agriculture is a composite interrelation among plants, microbes, and soil. Plant microbes play a major role in growth promotion and improve soil fertility as well. Bacillus spp. produces an extensive range of bio-chemicals that assist in plant disease control, promote plant development, and make them suitable for agricultural uses. Bacillus spp. support plant growth by N fixation, P and K solubilization, and phytohormone synthesis, in addition to being the most propitious biocontrol agent. Moreover, Bacilli excrete extracellular metabolites, including antibiotics, lytic enzymes, and siderophores, and demonstrate antagonistic activity against phytopathogens. Bacillus spp. boosts plant resistance toward pathogens by inducing systemic resistance (ISR). The most effective microbial insecticide against insects and pests in agriculture is Bacillus thuringiensis (Bt). Additionally, the incorporation of toxin genes in genetically modified crops increases resistance to insects and pests. There is a constant increase in the identified Bacillus species as potential biocontrol agents. Moreover, they have been involved in the biosynthesis of metallic nanoparticles. The main objective of this review article is to display the uses and application of Bacillus specie as a promising biopesticide in sustainable agriculture. Bacillus spp. strains that are antagonistic and promote plant yield attributes could be valuable in developing novel formulations to lead the way toward sustainable agriculture.

Microencapsulation of Bacillus Strains for Improving Wheat (Triticum turgidum Subsp. durum) Growth and Development

Bio-formulation technologies have a limited impact on agricultural productivity in developing countries, especially those based on plant growth-promoting rhizobacteria. Thus, calcium alginate microbeads were synthesized and used for the protection and delivery of three beneficial Bacillus strains for agricultural applications. The process of encapsulation had a high yield per gram for all bacteria and the microbeads protected the Bacillus strains, allowing their survival, after 12 months of storage at room temperature. Microbead analysis was carried out by observing the rate of swelling and biodegradation of the beads and the released-establishment of bacteria in the soil. These results showed that there is an increase of around 75% in bead swelling on average, which allows for larger pores, and the effective release and subsequent establishment of the bacteria in the soil. Biodegradation of microbeads in the soil was gradual: in the first week, they increased their weight (75%), which consistently results in the swelling ratio. The co-inoculation of the encapsulated strain TRQ8 with the other two encapsulated strains showed plant growth promotion. TRQ8 + TRQ65 and TRQ8 + TE3^T bacteria showed increases in different biometric parameters of wheat plants, such as stem height, root length, dry weight, and chlorophyll content. Thus, here we demonstrated that the application of alginate microbeads containing the studied strains showed a positive effect on wheat plants.

Fungal endophytes from salt-adapted plants confer salt tolerance and promote growth in wheat (Triticum aestivum L.) at early seedling stage

With increasing human global population, increased yield under saline conditions is a desirable trait for major food crops. Use of endophytes, isolated from halophytic hosts, seems to be an exciting approach for conferring salt tolerance to a salt-sensitive crop. Therefore, in the current study, fungal endophytes were isolated from halophytic plants' roots and their ability to withstand in vitro salt stress was evaluated. The fungal endophytes could withstand up to 1M NaCl concentrations and this tolerance was independent of their host or tissue source. When inoculated on salt-sensitive wheat seeds/seedlings, several of the endophytes showed a positive impact on germination and biomass-related parameters upon salt stress, both in vitro and under glasshouse conditions. One of the isolates from dicot plants (identified as Microsphaeropsis arundinis) could successfully colonize wheat and promote its growth under salt and no-salt conditions. Amongst the fungal isolates that are known to be natural endophytes of wheat, Chaetomium globosum was the best performing isolate and has previously been reported to be an effective biocontrol agent. Based on the results of our preliminary study, we suggest that these fungal endophytes could prove beneficial for enhancing the salt stress tolerance of wheat crop.

Microbial Diversity and Adaptation under Salt-Affected Soils: A Review

The salinization of soil is responsible for the reduction in the growth and development of plants. As the global population increases day by day, there is a decrease in the cultivation of farmland due to the salinization of soil, which threatens food security. Salt-affected soils occur all over the world, especially in arid and semi-arid regions. The total area of global salt-affected soil is 1 billion ha, and in India, an area of nearly 6.74 million ha−1 is salt-stressed, out of which 2.95 million ha−1 are saline soil (including coastal) and 3.78 million ha−1 are alkali soil. The rectification and management of salt-stressed soils require specific approaches for sustainable crop production. Remediating salt-affected soil by chemical, physical and biological methods with available resources is recommended for agricultural purposes. Bioremediation is an eco-friendly approach compared to chemical and physical methods. The role of microorganisms has been documented by many workers for the bioremediation of such problematic soils. Halophilic Bacteria, Arbuscular mycorrhizal fungi, Cyanobacteria, plant growth-promoting rhizobacteria and microbial inoculation have been found to be effective for plant growth promotion under salt-stress conditions. The microbial mediated approaches can be adopted for the mitigation of salt-affected soil and help increase crop productivity. A microbial product consisting of beneficial halophiles maintains and enhances the soil health and the yield of the crop in salt-affected soil. This review will focus on the remediation of salt-affected soil by using microorganisms and their mechanisms in the soil and interaction with the plants.

Maize growth response to different Bacillus strains isolated from a salt-marshland area under salinity stress

Maize (Zea mays) growth performance has been hindered due to the high soil salinity. Salinity is one of the most severe abiotic stresses that has led to growth imbalance and profitability of harvests in arid and semi-arid regions. Plants have taken advantage of salt-tolerant bacteria as plant growth-promoters to enhance growth and reduce the adverse effects of salinity through the regulation of some biochemical, physiological, and molecular features. Preferences for non-chemical, eco-friendly, and economical approaches have caused the inquiry of the Bacillus genus as a joint group of plant growth-promoting rhizobacteria known to alleviate salt-stress impacts. In the present study, halotolerant Bacillus strains were isolated from salt-marshland soil and characterized for their physiological, molecular, and biochemical properties. Twenty-four bacterial isolates collected from high saline fields of salt marshland were analyzed by MALDI-TOF MS proteome analysis, which confirmed the taxonomic affiliation with Bacillus cereus, Bacillus subtilis, Bacillus atrophaeus, and Bacillus thorngiensis. Applying the isolates on maize plants as bio-inoculant bacteria obviously increased the growth parameters (P < 0.01). Pot experiments showed that isolates 74 and 90 were the most prominent strains to minimize the harmful effects of salinity. Its effects are heightening the potassium/sodium ratio and K-Na selectivity in shoots and roots measured by flame atomic absorption photometry (AAS). Accordingly, Bacillus cereus isolate 74 showed a maximum increase in dry weights of the shoot (133.89%), root (237.08%), length of the shoot (125%), and root (119.44%) compared to the control condition. Our findings suggest that bacteria isolated from marshland may be an economical and simple means to increase plant growth and resistance to high salinity soil conditions.

Halotolerant Bacillus altitudinis WR10 improves salt tolerance in wheat via a multi-level mechanism

Soil salinity is an important abiotic stress factor that seriously affects the crop growth and yield. Use of plant-derived microorganisms is a promising strategy to alleviate salt stress. In a previous study, the endophytic strain Bacillus altitudinis WR10 isolated from wheat roots showed high salt resistance. In this study, we investigated the efficacy of WR10 in improving the salt tolerance of wheat and its potential mechanisms using a hydroponic test. Under salt stress, WR10 inoculation significantly increased the lengths and dry weights of the roots and shoots, indicating that WR10 improves wheat salt tolerance at the seedling stage. WR10 inoculation significantly reduced Na⁺ accumulation and enhanced K⁺, P, and Ca²⁺ uptake in salt-stressed plants, which can be attributed to the upregulated gene expression of H⁺-ATPase as well as the P-solubilizing and biofilm-producing characteristics of WR10. At the transcriptional level, L-ascorbate peroxidase (APX), glutathione (GSH) synthetase related to GSH biosynthesis, and phenylpropanoid biosynthesis genes (CYP73A, 4CL, and CAD) were significantly upregulated, whereas those of GSH metabolism genes (glutathione S-transferase and gamma-glutamyltranspeptidase) were significantly downregulated in WR10-applied wheat roots under salt stress. These changes increased the APX activity and GSH levels and resulted in a decrease in hydrogen peroxide levels. Additionally, a decrease in proline content was observed in WR10-inoculated plants under salt stress because of WR10-induced upregulation of proline dehydrogenase gene expression. These results provide supporting evidence that WR10 improves wheat salt tolerance via more than one mechanism and open a window of opportunity for WR10 application in salinized soil.

Progress and Applications of Plant Growth-Promoting Bacteria in Salt Tolerance of Crops

Saline soils are a major challenge in agriculture, and salinization is increasing worldwide due to climate change and destructive agricultural practices. Excessive amounts of salt in soils cause imbalances in ion distribution, physiological dehydration, and oxidative stress in plants. Breeding and genetic engineering methods to improve plant salt tolerance and the better use of saline soils are being explored; however, these approaches can take decades to accomplish. A shorter-term approach to improve plant salt tolerance is to be inoculated with bacteria with high salt tolerance or adjusting the balance of bacteria in the rhizosphere, including endosymbiotic bacteria (living in roots or forming a symbiont) and exosymbiotic bacteria (living on roots). Rhizosphere bacteria promote plant growth and alleviate salt stress by providing minerals (such as nitrogen, phosphate, and potassium) and hormones (including auxin, cytokinin, and abscisic acid) or by reducing ethylene production. Plant growth-promoting rhizosphere bacteria are a promising tool to restore agricultural lands and improve plant growth in saline soils. In this review, we summarize the mechanisms of plant growth-promoting bacteria under salt stress and their applications for improving plant salt tolerance to provide a theoretical basis for further use in agricultural systems.

What Did We Learn From Current Progress in Heat Stress Tolerance in Plants? Can Microbes Be a Solution?

Temperature is a significant parameter in agriculture since it controls seed germination and plant growth. Global warming has resulted in an irregular rise in temperature posing a serious threat to the agricultural production around the world. A slight increase in temperature acts as stress and exert an overall negative impact on different developmental stages including plant phenology, development, cellular activities, gene expression, anatomical features, the functional and structural orientation of leaves, twigs, roots, and shoots. These impacts ultimately decrease the biomass, affect reproductive process, decrease flowering and fruiting and significant yield losses. Plants have inherent mechanisms to cope with different stressors including heat which may vary depending upon the type of plant species, duration and degree of the heat stress. Plants initially adapt avoidance and then tolerance strategies to combat heat stress. The tolerance pathway involves ion transporter, osmoprotectants, antioxidants, heat shock protein which help the plants to survive under heat stress. To develop heat-tolerant plants using above-mentioned strategies requires a lot of time, expertise, and resources. On contrary, plant growth-promoting rhizobacteria (PGPRs) is a cost-effective, time-saving, and user-friendly approach to support and enhance agricultural production under a range of environmental conditions including stresses. PGPR produce and regulate various phytohormones, enzymes, and metabolites that help plant to maintain growth under heat stress. They form biofilm, decrease abscisic acid, stimulate root development, enhance heat shock proteins, deamination of ACC enzyme, and nutrient availability especially nitrogen and phosphorous. Despite extensive work done on plant heat stress tolerance in general, very few comprehensive reviews are available on the subject especially the role of microbes for plant heat tolerance. This article reviews the current studies on the retaliation, adaptation, and tolerance to heat stress at the cellular, organellar, and whole plant levels, explains different approaches, and sheds light on how microbes can help to induce heat stress tolerance in plants.

Combating Salinity Through Natural Plant Extracts Based Biostimulants: A Review

Enhanced crop growth and yield are the recurring concerns in agricultural field, considering the soaring world population and climate change. Abiotic stresses are one of the major limiting factors for constraining crop production, for several economically important horticultural crops, and contribute to almost 70% of yield gap. Salt stress is one of these unsought abiotic stresses that has become a consistent problem in agriculture over the past few years. Salinity further induces ionic, osmotic, and oxidative stress that result in various metabolic perturbations (including the generation of reactive oxygen, carbonyl, and nitrogen species), reduction in water potential (ψw), distorted membrane potential, membrane injury, altered rates of photosynthesis, leaf senescence, and reduced nitrogen assimilation, among others); thereby provoking a drastic reduction in crop growth and yield. One of the strategies to mitigate salt stress is the use of natural plant extracts (PEs) instead of chemical fertilizers, thus limiting water, soil, and environmental pollution. PEs mainly consist of seeds, roots, shoots, fruits, flowers, and leaves concentrates employed either individually or in mixtures. Since PEs are usually rich in bioactive compounds (e.g., carotenoids, flavonoids, phenolics, etc.), therefore they are effective in regulating redox metabolism, thereby promoting plant growth and yield. However, various factors like plant growth stage, doses applied, application method, soil, and environmental conditions may greatly influence their impact on plants. PEs have been reported to enhance salt tolerance in plants primarily through modulation of signaling signatures and pathways (e.g., Na+, ANNA4, GIPC, SOS3, and SCaBP8 Ca2+ sensors, etc.), and regulation of redox machinery [e.g., superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), non-specific peroxidase (POX), glutathione peroxidase (GPX), peroxiredoxin (Prx), ascorbic acid (AsA), glutathione (GSH), α-tocopherol, etc.]. The current study highlights the role of PEs in terms of their sources, methods of preparation, and mode of action with subsequent physiological changes induced in plants against salinity. However, an explicit mode of action of PEs remains nebulous, which might be explicated utilizing transcriptomics, proteomics, metabolomics, and bioinformatics approaches. Being ecological and economical, PEs might pave the way for ensuring the food security in this challenging era of climate change.

Management of abiotic stresses by microbiome-based engineering of the rhizosphere

Abiotic stresses detrimentally affect both plant and soil health, threatening food security in an ever-increasing world population. Sustainable agriculture is necessary to augment crop yield with simultaneous management of stresses. Limitations of conventional bioinoculants has shifted the focus on more effective alternatives. With the realisation of the potential of rhizospheric microbiome engineering in enhancing plant's fitness under stresses, efforts have accelerated in this direction. Though still in its infancy, microbiome-based engineering has gained popularity because of its advantages over microbe-based approach. This review briefly presents major abiotic stresses afflicting arable land, followed by introduction to the conventional approach of microbe-based enhancement of plant attributes and stress mitigation with its inherent limitations. It then focusses on the significance of rhizospheric microbiome, and harnessing its potential by its strategic engineering for stress management. Further, success stories related to two major approaches of microbiome engineering (generation of synthetic microbial community/consortium, and host-mediated artificial selection) pertaining to stress management have been critically presented. Together with bringing forth the challenges associated with wide application of rhizospheric microbiome engineering in agriculture, the review proposes the adoption of combinatorial scheme for the same, bringing together ecological and reductionist approaches for improvised sustainable agricultural practices.

Plant growth promoting characteristics of halophilic and halotolerant bacteria isolated from coastal regions of Saurashtra Gujarat

Halophiles are a class of microorganisms that thrive in environments with very high salt concentrations. The coastal regions of Saurashtra Gujarat host a diverse group of microorganisms including halophilic and halotolerant bacteria that may have plant growth promoting characteristics. Microorganisms with plant growth promoting characteristics are of immense importance in the field of agriculture and the present study was conducted to investigate the characteristics of halophilic and halotolerant bacteria isolated from agricultural soils of coastal regions of Junagadh and Porbandar districts of Saurashtra, Gujarat. A total of 15 isolated strains showed indole acetic acid production, solubilization of phosphate and potash, and nitrogen fixing capacity ranging from 18.77-33.48 μg ml^-1, 50.10-106.10%, 180.42-239.92% and 0.170-0.480 g kg^-1 of Jensen's agar medium, respectively, while two isolates were also found positive for siderophore production. Besides, nine out of fifteen isolates also showed positive ACC deaminase activity ranging from 0.92-5.78 µM α-ketobutyrate mg^-1 h^-1. The isolates were further characterized by physiological, microscopic, and biochemical tests. The halophilic and halotolerant bacterial isolates were identified by 16S rRNA gene sequencing as belonging to Halomonas pacifica, H. stenophila, and Bacillus haynesii, B. licheniformis and Oceanobacillus aidingensis respectively. The 16S rRNA partial gene sequence of two isolates belonging to H. pacifica and H. stenophila were submitted to NCBI with accession number MK955347 and MK961217 respectively. The findings of the present investigation showed that isolated bacterial halophiles possess promising plant growth promoting characteristics. Their potential as bioinoculants to alleviate salinity stress in crops and for bioremediation deserves further investigation.

Wheat Microbiome: Structure, Dynamics, and Role in Improving Performance Under Stress Environments

Wheat is an important cereal crop species consumed globally. The growing global population demands a rapid and sustainable growth of agricultural systems. The development of genetically efficient wheat varieties has solved the global demand for wheat to a greater extent. The use of chemical substances for pathogen control and chemical fertilizers for enhanced agronomic traits also proved advantageous but at the cost of environmental health. An efficient alternative environment-friendly strategy would be the use of beneficial microorganisms growing on plants, which have the potential of controlling plant pathogens as well as enhancing the host plant's water and mineral availability and absorption along with conferring tolerance to different stresses. Therefore, a thorough understanding of plant-microbe interaction, identification of beneficial microbes and their roles, and finally harnessing their beneficial functions to enhance sustainable agriculture without altering the environmental quality is appealing. The wheat microbiome shows prominent variations with the developmental stage, tissue type, environmental conditions, genotype, and age of the plant. A diverse array of bacterial and fungal classes, genera, and species was found to be associated with stems, leaves, roots, seeds, spikes, and rhizospheres, etc., which play a beneficial role in wheat. Harnessing the beneficial aspect of these microbes is a promising method for enhancing the performance of wheat under different environmental stresses. This review focuses on the microbiomes associated with wheat, their spatio-temporal dynamics, and their involvement in mitigating biotic and abiotic stresses.

Interaction Between Halotolerant Phosphate-Solubilizing Bacteria (Providencia rettgeri Strain TPM23) and Rock Phosphate Improves Soil Biochemical Properties and Peanut Growth in Saline Soil

Soil salinity has adverse effects on soil microbial activity and nutrient cycles and therefore limits crop growth and yield. Amendments with halotolerant phosphate-solubilizing bacteria (PSB) and rock phosphate (RP) may improve properties of saline soil. In this study, we investigated the effects of RP either alone or in combination with PSB (Providencia rettgeri strain TPM23) on peanut growth and soil quality in a saline soil. With the combined application of RP and PSB, plant length and biomass (roots and shoots) and uptake of phosphorus (P), nitrogen (N), and potassium (K) increased significantly. Soil Na+ and Cl- contents decreased in the PR alone or PR combined with PSB treatment groups. There were strongly synergistic effects of RP and PSB on soil quality, including a decrease in pH. The soil available N, P, and K contents were significantly affected by the PSB treatments. In addition, the alkaline phosphomonoesterases, urease, and dehydrogenase activities increased significantly compared with the untreated group; highest alkaline phosphomonoesterases activity was observed in the RP and PSB treatment groups. The composition of rhizosphere soil bacterial communities was determined using 454-pyrosequencing of the 16S rRNA gene. In the PR alone or PR combined with PSB treatment groups, the structure of the soil bacterial community improved with increasing richness and diversity. With PSB inoculation, the relative abundance of Acidobacteria, Chloroflexi, and Planctomycetes increased. The three phyla were also positively correlated with soil available N and root dry weight. These results suggested microbiological mechanisms by which the combined use of RP and PSB improved saline soil and promoted plant growth. Overall, the study indicates the combined use of RP and PSB can be an economical and sustainable strategy to increase plant growth in P-deficient and salt-affected soils.

Understanding the potential of root microbiome influencing salt-tolerance in plants and mechanisms involved at the transcriptional and translational level

Soil salinity severely affects plant growth and development and imparts inevitable losses to crop productivity. Increasing the concentration of salts in the vicinity of plant roots has severe consequences at the morphological, biochemical, and molecular levels. These include loss of chlorophyll, decrease in photosynthetic rate, reduction in cell division, ROS generation, inactivation of antioxidative enzymes, alterations in phytohormone biosynthesis and signaling, and so forth. The association of microorganisms, viz. plant growth-promoting rhizobacteria, endophytes, and mycorrhiza, with plant roots constituting the root microbiome can confer a greater degree of salinity tolerance in addition to their inherent ability to promote growth and induce defense mechanisms. The mechanisms involved in induced stress tolerance bestowed by these microorganisms involve the modulation of phytohormone biosynthesis and signaling pathways (including indole acetic acid, gibberellic acid, brassinosteroids, abscisic acid, and jasmonic acid), accumulation of osmoprotectants (proline, glycine betaine, and sugar alcohols), and regulation of ion transporters (SOS1, NHX, HKT1). Apart from this, salt-tolerant microorganisms are known to induce the expression of salt-responsive genes via the action of several transcription factors, as well as by posttranscriptional and posttranslational modifications. Moreover, the potential of these salt-tolerant microflora can be employed for sustainably improving crop performance in saline environments. Therefore, this review will briefly focus on the key responses of plants under salinity stress and elucidate the mechanisms employed by the salt-tolerant microorganisms in improving plant tolerance under saline environments.

Salinity Stress: Toward Sustainable Plant Strategies and Using Plant Growth-Promoting Rhizobacteria Encapsulation for Reducing It

Salinity is one of the most important abiotic stresses that influences plant growth and productivity worldwide. Salinity affects plant growth by ionic toxicity, osmotic stress, hormonal imbalance, nutrient mobilization reduction, and reactive oxygen species (ROS). To survive in saline soils, plants have developed various physiological and biochemical strategies such as ion exchange, activation of antioxidant enzymes, and hormonal stimulation. In addition to plant adaption mechanisms, plant growth-promoting rhizobacteria (PGPR) can enhance salt tolerance in plants via ion homeostasis, production of antioxidants, ACC deaminase, phytohormones, extracellular polymeric substance (EPS), volatile organic compounds, accumulation of osmolytes, activation of plant antioxidative enzymes, and improvement of nutrients uptake. One of the important issues in microbial biotechnology is establishing a link between the beneficial strains screened in the laboratory with industry and the consumer. Therefore, in the development of biocontrol agents, it is necessary to study the optimization of conditions for mass reproduction and the selection of a suitable carrier for their final formulation. Toward sustainable agriculture, the use of appropriate formulations of bacterial agents as high-performance biofertilizers, including microbial biocapsules, is necessary to improve salt tolerance and crop productivity.

Modulation of Secondary Metabolites: A Halotolerance Strategy of Plant Growth Promoting Rhizobacteria Against Sodium Chloride Stress

An experiment was conducted to evaluate the role of bacterial secondary metabolites against induced salt stress. Five bacterial strains were isolated from three different habitats: Khewra salt range, oily sludge field in Chakwal, and garden soil of Quaid-i-Azam University Islamabad, Pakistan. The 16S rRNA gene and BLAST analysis of bacterial strains showed 99% sequence similarity with Pseudomonas putida AMUPP-2 (KM435273), Lysinibacillus sphaericus OUG29GKBB (KM972671), Bacillus pumilus MB431 (KP723538) isolated from salt range, Pseudomonas fluorescens B8 (KF010368) from garden soil and Exiguobacterium aurantiacum SPD2 (KX121703) from oily sludge, respectively. Pseudomonas fluorescens produced 294.98 µg/g of proline in the M9 medium supplemented with 125 mM NaCl, but its growth rate was decreased from 1.81 to 0.37. The P. putida showed faster growth rate even than control at 125 mM NaCl. B. pumilus and L. sphaericus did not show any decline in growth rate up to 100 mM NaCl. The synthesis of new amino acids were recorded at 125 mM NaCl stress, e.g., Pro, Leu, Arg in P. fluorescens and L. sphaericus, Pro, Lys, Phe, Ala in P. putida, Lys, Ala in B. pumilus, Met, Val, and Ala in E. aurantiacum. Liquid chromatography-mass spectrometry analysis of ethyl acetate extract of P. putida and L. sphaericus demonstrated that NaCl (125mM) induced the production of 3-oxo-C₁₂ homoserine lactone, oxosteroids, and steroid esters in addition to steroidal alkaloid lysophosphatidylcholines, antibiotics phenazine-1 carboxamide, 2,4-diacetyl phloroglucinol, carbazole, phosphatidylcholine, phosphatidyl ethanol amine, and salicylic acid as signaling compound. It was concluded that P. putida and L. sphaericus could be exploited for the production of secondary metabolites that have a wide range of implications in biotic and abiotic stresses and for the production of important pharmaceutical products.

Bioprospecting Desert Plants for Endophytic and Biostimulant Microbes: A Strategy for Enhancing Agricultural Production in a Hotter, Drier Future

Simple Summary

Endophytes are microbes that live inside plants without causing negative effects in their hosts. All land plants are known to have endophytes, and these endophytes have the capacity to be transferred between plants. Taking endophytes from desert plants, which grow in low-nutrient, high-stress environments, and transferring them to crop plants may alleviate some of the challenges being faced by the agricultural industry, such as increasing drought frequency and rising opposition to chemical use in agriculture. Studies have shown that desert endophytes have the capacity to increase nutrient uptake and increase plant resistance to drought and heat stress, salt stress, and pathogen attack. Currently, the agricultural industry focuses on using irrigation, chemical fertilizers, and chemical pesticides to solve such issues, which can be extremely damaging to the environment. While there is still a lot that is unknown about endophytes, particularly desert plant endophytes, current research provides evidence that desert plant endophytes could be an environmentally friendly alternative to the conventional solutions being applied today.

Abstract

Deserts are challenging places for plants to survive in due to low nutrient availability, drought and heat stress, water stress, and herbivory. Endophytes—microbes that colonize and infect plant tissues without causing apparent disease—may contribute to plant success in such harsh environments. Current knowledge of desert plant endophytes is limited, but studies performed so far reveal that they can improve host nutrient acquisition, increase host tolerance to abiotic stresses, and increase host resistance to biotic stresses. When considered in combination with their broad host range and high colonization rate, there is great potential for desert endophytes to be used in a commercial agricultural setting, especially as croplands face more frequent and severe droughts due to climate change and as the agricultural industry faces mounting pressure to break away from agrochemicals towards more environmentally friendly alternatives. Much is still unknown about desert endophytes, but future studies may prove fruitful for the discovery of new endophyte-based biofertilizers, biocontrol agents, and abiotic stress relievers of crops.

Salt-Tolerant Compatible Microbial Inoculants Modulate Physio-Biochemical Responses Enhance Plant Growth, Zn Biofortification and Yield of Wheat Grown in Saline-Sodic Soil

A wide range of root-associated mutualistic microorganisms have been successfully applied and documented in the past for growth promotion, biofertilization, biofortification and biotic and abiotic stress amelioration in major crops. These microorganisms include nitrogen fixers, nutrient mobilizers, bio-remediators and bio-control agents. The present study aimed to demonstrate the impact of salt-tolerant compatible microbial inoculants on plant growth; Zn biofortification and yield of wheat (Triticum aestivum L.) crops grown in saline-sodic soil and insight of the mechanisms involved therein are being shared through this paper. Field experiments were conducted to evaluate the effects of Trichoderma harzianum UBSTH-501 and Bacillus amyloliquefaciens B-16 on wheat grown in saline-sodic soil at Research Farm, ICAR-Indian Institute of Seed Sciences, Kushmaur, India. The population of rhizosphere-associated microorganisms changed dramatically upon inoculation of the test microbes in the wheat rhizosphere. The co-inoculation induced a significant accumulation of proline and total soluble sugar in wheat at 30, 60, 90 and 120 days after sowing as compared to the uninoculated control. Upon quantitative estimation of organic solutes and antioxidant enzymes, these were found to have increased significantly in co-inoculated plants under salt-stressed conditions. The application of microbial inoculants enhanced the salt tolerance level significantly in wheat plants grown in saline-sodic soil. A significant increase in the uptake and translocation of potassium (K⁺) and calcium (Ca²⁺) was observed in wheat co-inoculated with the microbial inoculants, while a significant reduction in sodium (Na⁺) content was recorded in plants treated with both the bio-agents when compared with the respective uninoculated control plants. Results clearly indicated that significantly higher expression of TaHKT-1 and TaNHX1 in the roots enhances salt tolerance effectively by maintaining the Na⁺/K⁺ balance in the plant tissue. It was also observed that co-inoculation of the test inoculants increased the expression of ZIP transporters (2–3.5-folds) which ultimately led to increased biofortification of Zn in wheat grown in saline-sodic soil. Results suggested that co-inoculation of T. harzianum UBSTH-501 and B. amyloliquefaciens B-16 not only increased plant growth but also improved total grain yield along with a reduction in seedling mortality in the early stages of crop growth. In general, the present investigation demonstrated the feasibility of using salt-tolerant rhizosphere microbes for plant growth promotion and provides insights into plant-microbe interactions to ameliorate salt stress and increase Zn bio-fortification in wheat.

A Review of Recent Advances and Future Directions in the Management of Salinity Stress in Finger Millet

Salinity stress is a major environmental impediment affecting the growth and production of crops. Finger millet is an important cereal grown in many arid and semi-arid areas of the world characterized by erratic rainfall and scarcity of good-quality water. Finger millet salinity stress is caused by the accumulation of soluble salts due to irrigation without a proper drainage system, coupled with the underlying rocks having a high salt content, which leads to the salinization of arable land. This problem is projected to be exacerbated by climate change. The use of new and efficient strategies that provide stable salinity tolerance across a wide range of environments can guarantee sustainable production of finger millet in the future. In this review, we analyze the strategies that have been used for salinity stress management in finger millet production and discuss potential future directions toward the development of salt-tolerant finger millet varieties. This review also describes how advanced biotechnological tools are being used to develop salt-tolerant plants. The biotechnological techniques discussed in this review are simple to implement, have design flexibility, low cost, and highly efficient. This information provides insights into enhancing finger millet salinity tolerance and improving production.

Characterization and Comparison of Bacterial Communities of an Invasive and Two Native Caribbean Seagrass Species Sheds Light on the Possible Influence of the Microbiome on Invasive Mechanisms

Invasive plants, including marine macrophytes, are one of the most important threats to biodiversity by displacing native species and organisms depending on them. Invasion success is dependent on interactions among living organisms, but their study has been mostly limited to negative interactions while positive interactions are mostly underlooked. Recent studies suggested that microorganisms associated with eukaryotic hosts may play a determinant role in the invasion process. Along with the knowledge of their structure, taxonomic composition, and potential functional profile, understanding how bacterial communities are associated with the invasive species and the threatened natives (species-specific/environmentally shaped/tissue-specific) can give us a holistic insight into the invasion mechanisms. Here, we aimed to compare the bacterial communities associated with leaves and roots of two native Caribbean seagrasses (Halodule wrightii and Thalassia testudinum) with those of the successful invader Halophila stipulacea, in the Caribbean island Curaçao, using 16S rRNA gene amplicon sequencing and functional prediction. Invasive seagrass microbiomes were more diverse and included three times more species-specific core OTUs than the natives. Associated bacterial communities were seagrass-specific, with higher similarities between natives than between invasive and native seagrasses for both communities associated with leaves and roots, despite their strong tissue differentiation. However, with a higher number of OTUs in common, the core community (i.e., OTUs occurring in at least 80% of the samples) of the native H. wrightii was more similar to that of the invader H. stipulacea than T. testudinum, which could reflect more similar essential needs (e.g., nutritional, adaptive, and physiological) between native and invasive, in contrast to the two natives that might share more environment-related OTUs. Relative to native seagrass species, the invasive H. stipulacea was enriched in halotolerant bacterial genera with plant growth-promoting properties (like Halomonas sp. and Lysinibacillus sp.) and other potential beneficial effects for hosts (e.g., heavy metal detoxifiers and quorum sensing inhibitors). Predicted functional profiles also revealed some advantageous traits on the invasive species such as detoxification pathways, protection against pathogens, and stress tolerance. Despite the predictive nature of our findings concerning the functional potential of the bacteria, this investigation provides novel and important insights into native vs. invasive seagrasses microbiome. We demonstrated that the bacterial community associated with the invasive seagrass H. stipulacea is different from native seagrasses, including some potentially beneficial bacteria, suggesting the importance of considering the microbiome dynamics as a possible and important influencing factor in the colonization of non-indigenous species. We suggest further comparison of H. stipulacea microbiome from its native range with that from both the Mediterranean and Caribbean habitats where this species has a contrasting invasion success. Also, our new findings open doors to a more in-depth investigation combining meta-omics with bacterial manipulation experiments in order to confirm any functional advantage in the microbiome of this invasive seagrass.

Deep-Sea Actinobacteria Mitigate Salinity Stress in Tomato Seedlings and Their Biosafety Testing

Soil salinity is an enormous problem affecting global agricultural productivity. Deep-sea actinobacteria are interesting due to their salt tolerance mechanisms. In the present study, we aim to determine the ability of deep-sea Dermacoccus (D. barathri MT2.1^T and D. profundi MT2.2^T) to promote tomato seedlings under 150 mM NaCl compared with the terrestrial strain D. nishinomiyaensis DSM20448^T. All strains exhibit in vitro plant growth-promoting traits of indole-3-acetic acid production, phosphate solubilization, and siderophore production. Tomato seedlings inoculated with D. barathri MT2.1^T showed higher growth parameters (shoot and root length, dry weight, and chlorophyll content) than non-inoculated tomato and the terrestrial strain under 150 mM NaCl. In addition, hydrogen peroxide (H₂O₂) in leaves of tomatoes inoculated with deep-sea Dermacoccus was lower than the control seedlings. This observation suggested that deep-sea Dermacoccus mitigated salt stress by reducing oxidative stress caused by hydrogen peroxide. D. barathri MT2.1^T showed no harmful effects on Caenorhabditis elegans, Daphnia magna, Eisenia foetida, and Escherichia coli MC4100 in biosafety tests. This evidence suggests that D. barathri MT2.1^T would be safe for use in the environment. Our results highlight the potential of deep-sea Dermacoccus as a plant growth promoter for tomatoes under salinity stress.

Endophytic halotolerant Bacillus velezensis FMH2 alleviates salt stress on tomato plants by improving plant growth and altering physiological and antioxidant responses

Salinity stress has significant deleterious effects on agricultural lands and plant yields. Plants undergo a series of physiological and molecular changes to reduce salt-induced damage. However, these mechanisms remain insufficient. The inoculation of plant growth promoting bacteria to improve plant health under stress conditions offers promise. Bacillus velezensis FMH2 has been shown to protect tomato fruits against black mold disease and to improve seed tolerance to abiotic stresses. During this study, the major physiological and metabolic changes connected with FMH2 mitigation of abiotic stress tolerance in tomato plants were explored. In presence of different salt levels, FMH2 showed a high potentiality to colonize internal plant tissues and to produce several plant growth promoting metabolites such as siderophores, indole acetic acid, and hydrolytic enzymes. FMH2-treatment promoted plant growth (root structure, plant elongation, leaf emission, fresh and dry weights, water content, etc.) in absence as well as in presence of salt stress. FMH2 treatment decreased endogenous Na⁺ accumulation and increased K⁺ and Ca²⁺ uptake. Furthermore, B. velezensis FMH2-treatment improved chlorophyll contents, membrane integrity and phenol peroxidase concentrations, and reduced malondialdehyde and hydrogen peroxide levels under saline conditions with a significant salinity × strain interaction. The present study suggests the endophytic strain FMH2 involved different mechanisms and regulatory functions to enhance plant oxidative systems and regulate ion uptake mechanisms supporting both growth and stress management.

Plant Growth Promoting Rhizobacteria, Arbuscular Mycorrhizal Fungi and Their Synergistic Interactions to Counteract the Negative Effects of Saline Soil on Agriculture: Key Macromolecules and Mechanisms

Soil saltiness is a noteworthy issue as it results in loss of profitability and development of agrarian harvests and decline in soil health. Microorganisms associated with plants contribute to their growth promotion and salinity tolerance by employing a multitude of macromolecules and pathways. Plant growth promoting rhizobacteria (PGPR) have an immediate impact on improving profitability based on higher crop yield. Some PGPR produce 1-aminocyclopropane-1-carboxylic (ACC) deaminase (EC 4.1.99.4), which controls ethylene production by diverting ACC into α-ketobutyrate and ammonia. ACC deaminase enhances germination rate and growth parameters of root and shoot in different harvests with and without salt stress. Arbuscular mycorrhizal fungi (AMF) show a symbiotic relationship with plants, which helps in efficient uptake of mineral nutrients and water by the plants and also provide protection to the plants against pathogens and various abiotic stresses. The dual inoculation of PGPR and AMF enhances nutrient uptake and productivity of several crops compared to a single inoculation in both normal and stressed environments. Positively interacting PGPR + AMF combination is an efficient and cost-effective recipe for improving plant tolerance against salinity stress, which can be an extremely useful approach for sustainable agriculture.

Halotolerant Bacillus spizizenii FMH45 promoting growth, physiological, and antioxidant parameters of tomato plants exposed to salt stress

Bacillus spizizenii is for the first time described as a plant growth salt-tolerant bacterium able to alleviate salt stress in crop plants by improving physiological parameters and antioxidant defense mechanisms. Agricultural soil salinization is a serious issue worldwide affecting agricultural yield. Plant growth promoting bacteria can enhance salt tolerance and plant yield. Bacillus spizizenii FMH45 has been shown to inhibit fungal attacks in tomato fruits and to augment tomato seed germination in presence of abiotic stresses. During this study, we reported for the first time B. spizizenii as a salt-tolerant bacterium able to alleviate salt stress in tomato plants. B. spizizenii FMH45 was examined in vitro for its potential to produce several plant growth promoting characters (siderophores, IAA, and phosphate solubilization) and hydrolytic enzymes (cellulase, glucanase and protease) in the presence of saline conditions. FMH45 was also investigated in vivo in pot experiments to evaluate its ability to promote tomato plant growth under salt stress condition. FMH45 inoculation, enhanced tomato seedling length, vigor index, and plant fresh and dry weights when compared to the non-inoculated controls exposed and not exposed to a regular irrigation with salt solutions containing: 0; 3.5; 7; and 10 g L^-1 of NaCl. FMH45-treated plants also presented improved chlorophyll content, membrane integrity (MI), and phenol peroxidase (POX) concentrations, as well as reduced malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) levels under saline conditions with a significant salinity × strain interaction. Furthermore, FMH45 inoculation significantly decreased endogenous Na⁺ accumulation, increased K⁺ and Ca²⁺ uptake, and thereby improved K⁺/Na⁺ and Ca²⁺/Na⁺ ratios. This study proves that bio-inoculation of FMH45 efficiently increases salt tolerance in tomato plants. This sustainable approach can be applied to other stressed plant species in affected soils.

Mining the rhizosphere of halophytic rangeland plants for halotolerant bacteria to improve growth and yield of salinity-stressed wheat

In this study, the effects of three halotolerant rhizobacterial isolates AL, HR, and SB, which are able to grow at a salinity level of 1600 mM NaCl, with multiple plant growth promoting (PGP) traits on some seed and forage quality attributes, and vegetative, reproductive, biochemical and physiological characteristics of wheat plant irrigated with saline water (0, 40, 80, and 160 mM NaCl) were investigated. The ability of halotolerant bacterial isolates to produce PGP traits was affected by salinity levels, depending upon the bacterial isolates. Salinity stress significantly affected the yield, quality, and growth of wheat by modifying the morpho-physiological and biochemical traits of the exposed plants. However, all three bacterial isolates, especially isolate AL, significantly improved the biochemical (an increase in K⁺/Na⁺ ratio by 55%, plant P content by 50%, and plant Ca content by 31%), morphological (an increase in stem dry weight by 52%, root dry weight by 44%, spike dry weight by 34%, and grain dry weight by 43%), and physiological (an increase in leaf proline content by 50% and total phenol in leaf by 42%) attributes of wheat and aided the plant to tolerate salinity stress in contrast to un-inoculated plant. Plants inoculated with bacterial isolates showed significantly improved seed amylose by 36%, leaf crude protein by 30%, leaf metabolic energy by 37%, and leaf water-soluble sugar content by 34%. Among the measured PGP and plant attributes, bacterial auxin and plant K content were of key importance in increasing reproductive performance of wheat. The bacterial isolates AL, HR, and SB were identified as Bacillus safensis, B. pumilus, and Zhihengliuella halotolerans, respectively, based on 16 S rDNA sequence. The study reveals that application of halotolerant plant growth-promoting rhizobacteria isolated from halophytic rangeland plants can be a cost effective and ecological sustainable method to improve wheat productivity, especially the attributes related to seed and forage quality, under salinity stress conditions.

Seed biostimulant Bacillus sp. MGW9 improves the salt tolerance of maize during seed germination

Crop performance is seriously affected by high salt concentrations in soils. To develop improved seed pre-sowing treatment technologies, it is crucial to improve the salt tolerance of seed germination. Here, we isolated and identified the strain Bacillus sp. MGW9 and developed the seed biostimulant MGW9. The effects of seed biopriming with the seed biostimulant MGW9 in maize (Zea mays L.) under saline conditions were studied. The results show that the strain Bacillus sp. MGW9 has characteristics such as salt tolerance, nitrogen fixation, phosphorus dissolution, and indole-3-acetic acid production. Seed biopriming with the seed biostimulant MGW9 enhanced the performance of maize during seed germination under salinity stress, improving the germination energy, germination percentage, shoot/seedling length, primary root length, shoot/seedling fresh weight, shoot/seedling dry weight, root fresh weight and root dry weight. Seed biostimulant MGW9 biopriming also alleviated the salinity damage to maize by improving the relative water content, chlorophyll content, proline content, soluble sugar content, root activity, and activities of superoxide dismutase, catalase, peroxidase and ascorbate peroxidase, while decreasing the malondialdehyde content. In particular, the field seedling emergence of maize seeds in saline-alkali soil can be improved by biopriming with the seed biostimulant MGW9. Therefore, maize seed biopriming with the seed biostimulant MGW9 could be an effective approach to overcoming the inhibitory effects of salinity stress and promoting seed germination and seedling growth.

Comparative Study of the Rhizosphere and Root Endosphere Microbiomes of Cholistan Desert Plants

Microbial communities associated with the rhizosphere and roots of desert halophytes play an important role in plants’ growth and development. Very limited information has been available on the microbial diversity of arid environments of Pakistan. Hence in the current study, the microbial diversity of rhizosphere and root endosphere of desert halophytes, Zygophyllum simplex, Haloxylon salicoricum, Aerva javanica, and Capparis decidua was evaluated. The rhizosphere and root endosphere samples of desert halophytes collected from the three geographic sites of Cholistan desert, Punjab, Pakistan were analyzed by using 16S rRNA based Illumina sequencing. The results showed that Proteobacteria were more abundant in the rhizospheric soils while Actinobacteria were more dominant in the root endosphere of halophytes. Bacteroidetes, Firmicutes, and Deinococcus-Thermus were identified from all rhizospheric soils and roots across the three sites, with variable percentage. Bacillus, Kocuria, Pseudomonas, Halomonas, and Flavobacterium were commonly identified from the rhizosphere and root endosphere of halophytes across all the three sites. At the genus level, microbial diversity from Haloxylon showed the greatest variations between the rhizosphere and root endosphere from the site 2. This study revealed that microbial diversity analysis can be used to study how changes in abiotic factors such as soil moisture content and salinity affect the microbial communities associated with the rhizospheric soils and root endosphere of halophytes across the three sites. This study will also help in the discovery of potential inoculants for crops growing in arid and semi-arid regions of Pakistan.

Elsayed E, El Enshasy HA. Role of Bacillus cereus in Improving the Growth and Phytoextractability of Brassica nigra (L.) K. Koch in Chromium Contaminated Soil

Plant growth-promoting rhizobacteria (PGPR) mediate heavy metal tolerance and improve phytoextraction potential in plants. The present research was conducted to find the potential of bacterial strains in improving the growth and phytoextraction abilities of Brassica nigra (L.) K. Koch. in chromium contaminated soil. In this study, a total of 15 bacterial strains were isolated from heavy metal polluted soil and were screened for their heavy metal tolerance and plant growth promotion potential. The most efficient strain was identified by 16S rRNA gene sequencing and was identified as Bacillus cereus. The isolate also showed the potential to solubilize phosphate and synthesize siderophore, phytohormones (indole acetic acid, cytokinin, and abscisic acid), and osmolyte (proline and sugar) in chromium (Cr+3) supplemented medium. The results of the present study showed that chromium stress has negative effects on seed germination and plant growth in B. nigra while inoculation of B. cereus improved plant growth and reduced chromium toxicity. The increase in seed germination percentage, shoot length, and root length was 28.07%, 35.86%, 19.11% while the fresh and dry biomass of the plant increased by 48.00% and 62.16%, respectively, as compared to the uninoculated/control plants. The photosynthetic pigments were also improved by bacterial inoculation as compared to untreated stress-exposed plants, i.e., increase in chlorophyll a, chlorophyll b, chlorophyll a + b, and carotenoid was d 25.94%, 10.65%, 20.35%, and 44.30%, respectively. Bacterial inoculation also resulted in osmotic adjustment (proline 8.76% and sugar 28.71%) and maintained the membrane stability (51.39%) which was also indicated by reduced malondialdehyde content (59.53% decrease). The antioxidant enzyme activities were also improved to 35.90% (superoxide dismutase), 59.61% (peroxide), and 33.33% (catalase) in inoculated stress-exposed plants as compared to the control plants. B. cereus inoculation also improved the uptake, bioaccumulation, and translocation of Cr in the plant. Data showed that B. cereus also increased Cr content in the root (2.71-fold) and shoot (4.01-fold), its bioaccumulation (2.71-fold in root and 4.03-fold in the shoot) and translocation (40%) was also high in B. nigra. The data revealed that B. cereus is a multifarious PGPR that efficiently tolerates heavy metal ions (Cr+3) and it can be used to enhance the growth and phytoextraction potential of B. nigra in heavy metal contaminated soil.

Biodiversity and antimicrobial potential of bacterial endophytes from halophyte Salicornia brachiata

Extreme natural habitats like halophytes, marsh land, and marine environment are suitable arena for chemical ecology between plants and microbes having environmental impact. Endophytes are an ecofriendly option for the promotion of plant growth and to serve as sustainable resource of novel bioactive natural products. The present study, focusing on biodiversity of bacterial endophytes from Salicornia brachiata, led to isolation of around 336 bacterial endophytes. Phylogenetic analysis of 63 endophytes revealed 13 genera with 27 different species, belonging to 3 major groups: Firmicutes, Proteobacteria, and Actinobacteria. 30% endophytic isolates belonging to various genera demonstrated broad-spectrum antibacterial and antifungal activities against a panel of human, plant, and aquatic infectious agents. An endophytic isolate Bacillus amyloliquefaciens 5NPA-1, exhibited strong in-vitro antibacterial activity against human pathogen Staphylococcus aureus and phytopathogen Xanthomonas campestris. Investigation through LC-MS/MS-based molecular networking and bioactivity-guided purification led to the identification of three bioactive compounds belonging to lipopeptide class based on ¹H-, ¹³C-NMR and MS analysis. To our knowledge, this is the first report studying bacterial endophytic biodiversity of Salicornia brachiata and the isolation of bioactive compounds from its endophyte. Overall, the present study provides insights into the diversity of endophytes associated with the plants from the extreme environment as a rich source of metabolites with remarkable agricultural applications and therapeutic properties.

Plant growth-promoting rhizobacteria isolation from rhizosphere of submerged macrophytes and their growth-promoting effect on Vallisneria natans under high sediment organic matter load

Sediment organic matter is a key stressor for submerged macrophyte growth, which negatively impacts the ecological restoration of lakes. Plant growth-promoting rhizobacteria (PGPR) were screened from the rhizosphere of submerged macrophytes and used due to their promoting effect on Vallisneria natans under a high sediment organic matter load. Root exudates were used as the sole carbon source to obtain the root affinity strains. Eight isolates were selected from the 61 isolated strains, based on the P solubilization, IAA production, cytokinins production and ACC deaminase activity. The analysis of the 16S rDNA indicated that one strain was Staphylococcus sp., while the other seven bacterial strains were Bacillus sp. They were all listed in low-risk groups for safety use in agricultural practices. The plant height significantly increased after inoculation with PGPR strains, with the highest rate of increase reaching 96%. This study provides an innovative technique for recovering submerged macrophytes under sediment organic matter stress.

Dual Microbial Inoculation, a Game Changer? - Bacterial Biostimulants With Multifunctional Growth Promoting Traits to Mitigate Salinity Stress in Spring Mungbean

Soil microbes play a vital role in improving plant growth, soil health, ameliorate biotic/abiotic stress and enhance crop productivity. The present study was aimed to investigate a coordinated effect of compatible consortium [salt tolerating Rhizobium and rhizobacterium with 1-aminocyclopropane-1-carboxylate (ACC) deaminase] in enhancing plant growth promoting (PGP) traits, symbiotic efficiency, nutrient acquisition, anti-oxidative enzymes, grain yield and associated profitability in spring mungbean. We identified a non-pathogenic compatible Rhizobium sp. LSMR-32 (MH644039.1) and Enterococcus mundtii LSMRS-3 (MH644178.1) from salt affected areas of Punjab, India and the same were assessed to develop consortium biofertilizer based on salt tolerance, multifarious PGP traits, antagonistic defense activities and presence of nifH, acds, pqq, and ipdc genes. Indole Acetic acid (IAA), P-solubilization, biofilm formation, exo-polysaccharides, siderophore, salt tolerance, ACC deaminase activities were all found highly significant in dual inoculant (LSMR-32 + LSMRS-3) treatment compared to LSMR-32 alone. Under saline soil conditions, dual inoculant showed a higher seed germination, plant height, biomass, chlorophyll content and macro and micro-nutrient uptake, than un-inoculated control. However, symbiotic (nodulation, nodule biomass and leghaemoglobin content) and soil quality parameters (phosphatase and soil dehydrogenase enzymes) increased numerically with LSMR-32 + LSMRS-3 over Rhizobium sp. LSMR-32 alone. Dual bacterial inoculation (LSMR-32 + LSMRS-3) increased the proline content (2.05 fold), anti-oxidative enzymes viz., superoxide dismutase (1.50 fold), catalase (1.43 fold) and peroxidase (3.88 folds) in contrast to control treatment. Decreased Na⁺ accumulation and increased K⁺ uptake resulted in favorable K⁺/Na⁺ ratio through ion homeostasis. Co-inoculation of Rhizobium sp. LSMR-32 and Enterococcus mundtii LSMRS-3 significantly improved the grain yield by 8.92% and led to superior B: C ratio over Rhizobium sp. alone under salt stress. To best of our knowledge this is perhaps the first field report from Indian soils that largely describes dual inoculation of Rhizobium sp. LSMR-32 and Enterococcus mundtii LSMRS-3 and the same can be considered as a game-changer approach to simultaneously induce salt tolerance and improve productivity in spring mungbean under saline stress conditions.