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Environmental stress affects food productivity by producing reactive oxygen species (ROS) that damage cell organelles and biomolecules, leading to apoptosis. Plants have developed a variety of defense responses over time to counteract the detrimental effects of biotic and abiotic stresses. However, in order to combat climate change and the deterioration of ecosystems, it will be necessary to promote the use of beneficial bacteria including plant growth-promoting bacteria (PGPR) in agricultural ecosystems. PGPR potentially improves nutrient absorption, modulates hormone levels, and/or improves tolerance to abiotic stress factors and plant pathogens. PGPR offers a sustainable replacement for conventional agrochemicals and traditional farming practices by improving plant growth and stress tolerance. In this context, studying the fundamental evolutionary and ecological relationships among plants and their microbiomes is necessary to build vital approaches to strengthen traditional agricultural techniques. Stress-tolerant PGPR can release bioactive substances such as gibberellins and indole acetic acid which participate in mitigating stresses. PGPR could minimize the adverse effect of salinity, drought, heavy metals, floods, and other stresses on plants by inducing antioxidant enzymes, like catalase, peroxidase, and superoxide dismutase. This review summarizes the current developments in the PGPR-based strategy for tackling biotic and abiotic stresses. [ABSTRACT FROM AUTHOR]

Salinity is one of the most significant constraints to crop production in dry parts of the world. This research emphasizes the beneficial effects of plant growth-promoting rhizo- bacterial isolates (PGPR) on the physiological responses of maize and wheat in a saline (NaCl) environment. Soil samples for the study were collected from a maize field in Baddi, Himachal Pradesh, India. Isolated bacterial strains were screened for salt (NaCl) toler- ance and plant growth-promoting characters (i.e., indole acetic acid (IAA) production, siderophore production, amino cyclopropane-1-carboxylic acid (ACC) deaminase activ- ity, hydrogen cyanide (HCN) production, and mineral phosphate solubilization). Screened bacterial isolates were further tested in pot experiments to examine their effects on wheat and maize growth. The treatments included five levels of bacterial inoculation (P0: control, P1: ACC deaminase positive + siderophore producer + NaCl tolerant bacteria, P2: mineral phosphate solubilizer + HCN producer + NaCl tolerant bacteria, P3: IAA producer + ACC deaminase positive + NaCl tolerant bacteria, P4: bacterial consortium, P5: Phosphomax commercial biofertilizer) and salt stress at 6 dS/m. Research findings found that exposure to a bacterial consortium led to the highest growth parameter in maize, including shoot length, root length, shoot and root dry weight followed by P2, P3, and P5 treatments at 6 dS/m salinity levels. However, P2 showed the best results for wheat at the same salinity levels, followed by P3, P4 and P5 treatments. P1 treatment did not show a significant result compared to control at 6dS/m salt level for both crops. The maximum proline content in maize and wheat was observed in P4 (23.28 μmol · g−1 ) and P2 (15.52 μmol · g−1 ) treatments, respectively, followed by P5 with Phosphomax biofertilizer. Therefore, the study proposed the application of growth-promoting bacterial isolates as efficient biofertilizers in the Baddi region of Himachal Pradesh, India. [ABSTRACT FROM AUTHOR]

Zinc is an essential micronutrient necessary for optimal development of tomato (Solanum lycopersicum L.). Zinc-solubilizing microbes could be substitutes for zinc supplementation and transform inorganic zinc into accessible forms. The objective of the study was to culture and screen a variety of zinc-solubilizing bacteria (ZSB) from vermicompost for various plant growth-promoting (PGP) characteristics in tomato. Thirty-isolates from vermicompost were screened for Zn-solubilization and PGP activity. A quantitative assessment of Zn solubilization indicated maximum Zn solubilization was achieved with isolate VBZ4 (26.8 mg∙L−1) followed by isolate VBZ17 (22.2 mg∙L−1) on ZnO and 18.3 mg∙L−1 (isolate VBZ4), 15.6 mg∙mL−1 (isolate VBZ17) on ZnCO3 enriched media. The isolates were examined in association with tomato plants for growth, where isolate VBZ4 improved plant growth and maximum zinc content in tomato fruit (2.87 mg/100 g) followed by isolates VBZ4+ VBZ17 and isolate VBZ17 with 2.17 mg/100 g and 2.06 mg/100 g Zn content, respectively. Isolates VBZ4 and VBZ17 were identified as Pseudomonas sp. VBZ4 and P. stutzeri VBZ17. Application of these bacteria may help provide sufficient Zn bioavailability which could lead to improved plant growth in a sustainable manner. [ABSTRACT FROM AUTHOR]

Zinc is an essential micronutrient necessary for the optimal development and yield of Okra (Abelmoschus esculentus L.). Plants absorb zinc in soluble form as Zn2+; a large amount of zinc in the soil are in insoluble forms. Zinc solubilizing microbes could be substitutes for zinc fertilizers and transform inorganic zinc into plant accessible forms. The study was aimed to isolate and screen a range of Zinc solubilizing bacteria (ZSB) from vermicompost for their plant growth-promoting properties with okra. Thirty bacterial isolates from vermicompost were examined for zinc solubilization with ZnO and ZnCO3 using dilution plate method on Kings B medium. Two strains, i.e., VBZ4 and VBZ17, were found most prevalent Zn solubilizing isolates with 32 mm and 43 mm solubilization zone for ZnO supplemented media. Atomic absorption spectroscopy (AAS) was used for quantitative assessment of Zn solubilization, where VBZ4 displayed significantly higher solubility of ZnO (26.8 ppm) compared with VBZ17 (22.2 ppm). The quantitative results of plant growth promotion characters showed that VBZ4 and VBZ17 isolates to solubilize the maximum amount of phosphate with 316.72 μg/ml and 214.0 μg/ml, and indole acetic acid production, 10.2 μg/ml and 17.1 μg/ml respectively. Further, ZSB isolates were introduced with Okra seeds under pot experiment, where treatment P4 (seeds + VBZ4 + VBZ17) found significantly effective on plant growth and maximum zinc content in Okra fruit (2.85 mg/100g) compared to control. Application of these bacteria may help to provide sufficient amounts of Zn bioavailability, including improved plant growth in a sustainable manner. [ABSTRACT FROM AUTHOR]

Wheat and maize are the main staple food crops that contribute to human food security. Their growth, however, is reduced under stresses such as salinity. The plant microbiome is associated with each plant tissue and develops a holobiont in association with the plant. Plants actively manage the configuration of their related bacterial population and its function. These microorganisms provide a broad range of benefits and advantages to the plants. The present study aimed to examine the growth improvement of wheat var. HD 2687 and maize var. PSCL-4642 under salinity at the seedling stage following inoculation of salt-tolerant plant growth-promoting rhizobacteria (PGPR) BoGl120 purified from Bougainvillea glabra. The seed germination potential with/without bacterial inoculation was examined at 50, 100, 150, and 200 mM NaCl concentrations for both crops. Compared to controls, at 50 mM NaCl concentration, the BoGl120 isolate provided the maximum radicle length in maize (32 mm) and in wheat (24.8 mm). At 100 mM NaCl concentration, however, the radicle length of wheat and maize seedlings was decreased. Inoculation of plants with the BoGl120 isolate enhanced the plumule length of seedlings at different NaCl concentrations as compared to controls. In comparison with controls, BoGl120 improved the plumule length of wheat to 32.6, 14.0, and 8 mm at 50, 100, and 150 mM NaCl concentrations, respectively. The results of the present study support the concept that PGPRs could help to increase the tolerance against saline stress in wheat and maize at the seedling stage. [ABSTRACT FROM AUTHOR]

Wheat and corn crops contribute to the food security of humans by providing a nutrient-rich diet. However, their production in abiotic stress conditions such as salinity is limited. Endophytes exert a beneficial effect on plants through the decomposition of organic materials for smooth absorption, detoxification, and reduction of the effect of phytopathogenic microorganisms by increasing the immunity of host plants to resist phytopathogens and through nutrient deposition in plants responsible for reducing salt stress. The present study aimed to evaluate the NaCl tolerance efficiency of Triticum aestivum L. var. HD 2687 and Zea mays var. PSCL-4642 cultivars at the germination stage after inoculation with salt-tolerant bacterial endophyte BoGl21 isolated from Bougainvillea glabra. The seeds of both crops were tested for percentage of seed germination with/without bacteria at 50, 100, 150, and 200 mM NaCl concentrations. The BoGl21 isolate induced a significant increase in radicle length in corn (25.6 mm) as compared to that in wheat (10.3 mm) at 50 mM NaCl. However, at 100 mM NaCl, the radical length of wheat and corn seedlings was 5 mm and 8.8 mm, respectively. Inoculation of maize and wheat with the bacterial isolate significantly increased the plumule length of the germinated seeds as compared to that of controls. BoGl21 increased the plumule length of wheat as compared to that of the control seeds by 31.9, 11.7, and 4.8 mm at 50, 100, and 150 mM salinity stress, respectively. Inoculation of corn seeds with BoGl21 at the tested NaCl levels (50, 100, and 150 mM NaCl) increased the plumule length of the germinated seeds by 33.1, 22, 13.2, and 3.2 mm, respectively. The current research results support the hypothesis that bacterial endophytes could be beneficial to minimize the toxicity of saline stress on wheat and corn at the time of germination. [ABSTRACT FROM AUTHOR]

Globally, more than 5.2 billion hectares of farming fields are damaged through erosion, salinity, and soil deterioration. Salt stress-tolerant bacteria have plant growth-promoting (PGP) characteristics that can be used to overcome environmental stresses. Isolation and screening of salt-tolerant endophytes from Bougainvillea glabra were achieved through surface sterilization of leaves, followed by their cultivation on 0.5% NaCl-supplemented media. The performance of isolates for indole acetic acid (IAA) production, phosphate solubilization, ACC deaminase activity, ammonia production, siderophore production, and stress tolerance was determined. In the present study, 5 morphologically distinct salt-tolerant endophytic bacteria were cultured. Out of 5 isolates, 60% salt-tolerant endophytes showed phosphate solubilization, 100% IAA production, 40% ACC-deaminase activity, 100% siderophore production, 40% ammonia production and 60% HCN production. Dendrogram generated based on stress tolerance showed three clusters: clusters 1 and 2 containing two isolates and cluster 3 containing 1 isolate. Based on the highest PGP activities, BoGl17 and BoGl21 isolates were chosen and further tested for wheat and corn growth promotion. The isolates increased wheat shoot and root dry weight by 40% and 80%, and by 69% and 126% for BoGl17 and BoGl21, respectively. The bacterial isolates identified as Pseudomonas reidholzensis BoGl17 had 95.59% identity with Pseudomonas reidholzensis strain ID3, while the isolate Bacillus aerius BoGl21 had 90.96% identity with Bacillus aerius strain 24K based on phenotypic features and 16S rRNA gene sequencing results. Both isolates significantly improved plant growth as compared to uninoculated plants. [ABSTRACT FROM AUTHOR]

Globally more than 5.2 billion hectares of farming fields are damaged through erosion, salinity and soil deterioration. Many salt stress tolerant bacteria have plant growth promoting (PGP) characteristics that can be used to overcome environmental stresses. Isolation and screening of salt-tolerant endophytes from Salicornia brachiata were achieved through surface sterilization of leaves followed by cultivation on 4% NaCl amended media. Performance of isolates towards indole-3-acetic acid (IAA) production, phosphate solubilization, ACC deaminase activity, ammonia production, siderophore production and stress tolerance were determined. On the basis of the highest plant growth promoting activity, SbCT4 and SbCT7 isolates were tested for plant growth promotion with wheat and maize crops. In the present study, a total of 12 morphologically distinct salt-tolerant endophytic bacteria was cultured. Out of 12 isolates, 42% of salt-tolerant endophytes showed phosphate solubilization, 67% IAA production, 33% ACC-deaminase activity, 92% siderophore production, 41.6% ammonia production and 66% HCN production. A dendrogram, generated on the basis of stress tolerance, showed two clusters, each including five isolates. The bacterial isolates SbCT4 and SbCT7 showed the highest stress tolerance, and stood separately as an independent branch. Bacterial isolates increased wheat shoot and root dry weights by 60-82% and 50-100%, respectively. Similarly, improved results were obtained with maize shoot (27-150%) and root (80-126%) dry weights. For the first time from this plant the bacterial isolates were identified as Paenibacillus polymyxa SbCT4 and Bacillus subtilis SbCT7 based on phenotypic features and 16S rRNA gene sequencing. Paenibacillus polymyxa SbCT4 and B. subtilis SbCT7 significantly improved plant growth compared to non-inoculated trials. [ABSTRACT FROM AUTHOR]

Phytohormones play a very important role in enhancing plant growth by direct or indirect mechanisms involving plant-microbe interactions. Indole acetic acid (IAA) is one of the key phytohormones that directly enhance plant development. Kocuria rosea VB1 (GenBank ID: KY608093.1) and Arthrobacter luteolus VB2 (GenBank ID: KY608094.1) from polluted industrial water samples were characterized through a biochemical assay, 16S rDNA sequencing, and for promoting plant growth abilities. IAA production by VB1 and VB2 was tested in pure culture conditions supplemented with various L-tryptophan (Trp) concentrations (0, 50, 100, 200, and 500 μg @ ml!1). A significant difference in indole production by VB2 and VB1 inoculant at various L-Trp concentrations has been observed. VB1 has been reported to produce increased amounts of indole from 0.33 μg.ml-1 to 18.16 μg.ml-1, while the increase in indole production was from 0.63 μg .ml-1 to 9.22 μg.ml-1 for VB2 for various L-Trp concentrations. The VB1 strain produced 85.07 ng.ml-1 and 123.7 ng .ml-1 IAA, whereas the VB2 strain produced 70.3 ng.ml-1 and 78.4 ng.ml-1 IAA, respectively at 200 and 500 μg.ml-1 Trp concentrations. The growth pouch experiments with maize root exudates also showed a positive effect for both bacterial inoculants tested on IAA biosynthesis in comparison to non-inoculated seeds. Inoculation of maize seeds with VB2 and VB1 bacteria gave a significantly higher level of IAA production in comparison to non-inoculated seeds. Current study outcomes show the beneficial aspects of plant growth regulators produced by free-living bacteria which could play a significant role in plant growth promotion. [ABSTRACT FROM AUTHOR]

A variety of microorganisms generate highly potent surface-active bio-molecules or biosurfactants, which vary in their chemical properties and molecular size. In the present study, bioremediation effect of Pseudomonas fluorescence RE1 (GenBank: MF102882.1) and RE17 (GenBank: MF103672.1) endophytes on heavy metals Zn, Cr, Cd, and Ni were investigated. A total of 56 morphologically distinct isolates from indigenous rice roots were selected and subsequently characterised genotypically by using 16S rRNA sequencing approach. Next, biosurfactant production and heavy metal removal ability by the isolates were screened on the basis of α and β hemolysis on blood agar plates, BATH assay, and CTAB method. Analysis of bioremediation of heavy metals was done by using atomic adsorption spectroscopy. Bioremediation analysis revealed that isolates RE1 and RE17 reduced the concentration of Zn by up to 92% and 90% at pH 7.5, respectively, while for Ni, % removal was the same for both strains at 95% at pH 7.5. Biosorption results for Cr and Cd showed highest metal removal efficiency by Pseudomonas fluorescence RE17 at pH 8, 92% and 98%, respectively. Both isolates showed significant metal removal efficiency at 32±1 °C for all experimental heavy metals. The present study suggests that all endophytes withstand at high concentration of testing heavy metals and can be used for bioremediation of heavy metals in contaminated environments. [ABSTRACT FROM AUTHOR]

The use of plant growth promoting rhizobacteria is increasing in agriculture and gives an appealing manner to replace chemical fertilizers, pesticides, and dietary supplements. The objective of our research was to access the plant growth promotion traits of Pseudomonas aeruginosa, P. fluorescens and Bacillus subtilis isolated from the maize ( Zea mays L.) rhizosphere. In vitro studies showed that isolates have the potential to produce indole acetic acid (IAA), hydrogen cyanide, phosphate solubilisation, and siderophore. RNA analysis revealed that two isolates were 97% identical to P. aeruginosa strain DSM 50071 and P. aeruginosa strain NBRC 12689 (AK20 and AK31), while two others were 98% identical to P. fluorescens strain ATCC 13525, P. fluorescens strain IAM 12022 (AK18 and AK45) and one other was 99% identical to B. subtilis strain NCDO 1769 (AK38). Our gnotobiotic study showed significant differences in plant growth variables under control and inoculated conditions. In the present research, it was observed that the isolated strains had good plant growth promoting effects on rice. [ABSTRACT FROM AUTHOR]