Plant Growth Promoting Rhizobacteria Inoculation Research Articles

Plant growth-promoting rhizobacteria modulate induced corn defense against Spodoptera litura (Lepidoptera: Noctuidae).

Common cutworm, Spodoptera litura is an important pest of corn causing significant crop yield loss. Synthetic insecticides have mostly been used to combat this pest, raising human and environmental health concerns. Plant-growth promoting rhizobacteria (PGPR) could compensate for or augment the harmful effects of agrochemicals. Herein, we aimed to assess whether PGPR-induced defenses in corn plants impact the host-plant selection behavior of S. litura. Headspace volatile organic compounds (VOCs) were analyzed using Gas chromatography-mass spectrometry (GC-MS). Larvae fed inoculated corn exhibited lower weights and RGR than non-inoculated plants. Under choice experiments, PGPR-treated plants significantly reduced percentage leaf damage area and oviposition rate compared to untreated plants. VOC ratio emission varied significantly between control and PGPR treatments, which, in part, explains feeding and oviposition deterrence in PGPR-treated plants. The results demonstrate that PGPR inoculation can enhance corn resistance to S. litura, making it a promising candidate for crop protection strategies.

Restoration of fumigated soil biota with plant growth-promoting rhizobacteria to counteract Meloidogyne incognita (Tylenchida: Heteroderidae) boosts eggplant growth and defenses

AbstractThis study investigated the effectiveness of two plant growth-promoting rhizobacteria (PGPR) formulations, Bio Arc® 6% WP (BA, Bacillus megaterium) and BECTO Grow Roots® (BGR; Serratia marcescens, Pseudomonas putida, and P. fluorescens). Additionally, it focused on naturally infested soil that had undergone metam potassium fumigation to reduce root-knot nematode (RKN), specifically Meloidogyne incognita. It aimed to monitor eggplant response to soil biodiversity changes for 60 days of the experiment under greenhouse conditions. Our data showed that soil fumigation eliminated nematodes and reduced other microorganisms significantly. In sterilized soil, plant fresh root weight significantly decreased after the elimination of soil biota. Moreover, BGR achieved the highest plant growth vigor [fresh root (18.48%), fresh shoot (23.52%), and fresh plant weight (21.03%)], followed by BA [fresh root (11.98%), fresh shoot (20.77%), and fresh plant weight (16.38%), respectively]. Plant growth traits increased significantly following the second reinoculation of PGPR after a month. Also, the same data trend was observed in treatments inoculated with RKN + PGPR. Furthermore, BGR treatments exhibited consistent efficacy in controlling nematode infection, maintaining superior vegetative growth compared to BA treatments over time. However, BA treatments displayed a decline in plant growth when faced with repeated nematode infection. The range of gall, egg mass, and second-stage juvenile (J2s) numbers diminished after inoculation-infected plants with RKN and PGPR compared with infected plants alone. Biochemical changes in eggplant roots cultivated in sterilized soil exposed significant enhancement in total sugars, protein, and nonenzymatic antioxidants (flavonoids and phenolic content), with antioxidant activity enhanced upon inoculation of PGPR and RKN. Oppositely, the levels of enzymatic antioxidants (catalase, peroxidase, and superoxide dismutase) decreased significantly with single and double PGPR application. However, the decline was less pronounced in the BGR treatments than in BA. In contradiction of oxidative enzymes, reinoculated PGPR + RKN multiplied significantly in reinfested RKN treatments. Our findings support the use of PGPR combinations, in particular, for preventive inoculation against M. incognita. They also enhance plant growth-promoting factors and stimulate plant defenses against inevitable soil reinfestation following soil fumigation.

The Coupling Effects of PGPR Inoculation and Foliar Spraying of Strigolactone in Mitigating the Negative Effect of Salt Stress in Wheat Plants: Insights from Phytochemical, Growth, and Yield Attributes

Salt stress has detrimental effects on wheat plants at several physiological, biochemical, and molecular levels. This stress leads to suppressed growth, reduced grain yield, and poor quality of harvested grains. However, two approaches have shown promise for improving wheat salt tolerance: using a synthetic strigolactone analog called GR24 and applying plant growth-promoting rhizobacteria (PGPR). GR24 plays a vital role in regulating plant growth and development and in defense against various stresses. Conversely, PGPR are beneficial bacteria that colonize the rhizosphere of plants and promote their growth through multiple mechanisms. In our study, we investigated the effects of salinity on the growth and yield traits of two different wheat cultivars and explored the combined role of PGPR and GR24 in mitigating the impact of salt stress. We created three different salinity levels using NaCl in pots (original, 5 dS m−1, and 10 dS m−1) and inoculated wheat seeds with a salt-tolerant Bacillus velezensis UTB96 strain. In addition, we applied 10 μM GR24 via foliar application during the pollination stage. Our observations showed that salt stress negatively affected wheat’s growth, yield, and phytochemical properties compared to the control. However, both single and combined applications of PGPR and GR24 mitigated the adverse effects of salinity. The combined treatment had a more substantial impact than either alone in inducing and improving biochemical and ionic characteristics. These included decreasing Na+ content in both leaves and roots, and EL, H2O2, and MDA content in leaves while increasing K+ content in both leaves and roots, growth and yield-related traits, RWC, chlorophyll pigments, total protein, soluble sugar, starch, proline, GB, and antioxidant enzyme activity (APX, POX, and CAT) of leaves. In conclusion, integrating PGPR and GR24 can efficiently induce salt tolerance and improve plant growth under stressed conditions. This combined approach has the potential for broad applicability in supporting plant growth in the presence of salt stress.

Protective Role of Plant Growth Promoting Rhizobacteria Inoculation in the Development of Drought Tolerance in Shallot: Effects on Hydroxygen Peroxide Production, Lipid Peroxidation, and Secondary Metabolite Production

Protective Role of Plant Growth Promoting Rhizobacteria Inoculation in the Development of Drought Tolerance in Shallot: Effects on Hydroxygen Peroxide Production, Lipid Peroxidation, and Secondary Metabolite Production

Screening of plant growth-promoting rhizobacteria helps alleviate the joint toxicity of PVC+Cd pollution in sorghum plants

Combined microplastic and heavy metal pollution (M-HCP) has become a popular research topic due to the ability of these pollutants to have complex interactions. Plant growth-promoting rhizobacteria (PGPR) are widely used to alleviate stress from heavy metal pollution in plants. However, the effects and mechanisms by which these bacteria interact under M-HCP have not been extensively studied. In this study, we isolated and screened PGPR from M-HCP soils and analyzed the effects of these PGPR on sorghum growth and Cd accumulation under combined PVC+Cd pollution through pot experiments. The results showed that the length and biomass of sorghum plants grown in PVC+Cd contaminated soil were significantly lower than those grown in soils contaminated with Cd alone, revealing an enhancement in toxicity when the two contaminants were mixed. Seven isolated and screened PGPR strains effectively alleviated stress due to PVC+Cd contamination, which resulted in a significant enhancement in sorghum biomass. PGPR mitigated the decrease in soil available potassium, available phosphorus and alkali-hydrolyzable nitrogen content caused by combined PVC+Cd pollution and increased the contents of these soil nutrients. Soil treatment with combined PVC+Cd pollution and PGPR inoculation can affect rhizosphere bacterial communities and change the composition of dominant populations, such as Proteobacteria, Firmicutes, and Actinobacteria. PICRUSt 2 functional profile prediction revealed that combined PVC+Cd pollution and PGPR inoculation affected nitrogen fixation, nitrification, denitrification, organic phosphorus mineralization, inorganic phosphorus solubilization and the composition and abundance of genes related the N and P cycles. The Mantel test showed that functional strain abundance, the diversity index and N and P cycling-related genes were affected by test strain inoculation and were significant factors affecting sorghum growth, Cd content and accumulation. This study revealed that soil inoculation with isolated and screened PGPR can affect the soil inorganic nutrient content and bacterial community composition, thereby alleviating the stress caused by M-HCP and providing a theoretical basis and data support for the remediation of M-HCP.

Alleviation of heat stress by ACC Deaminase and Exopolysaccharide Producing Plant-Growth-Promoting Rhizobacteria in Solanum melongena L.

Background: The current study was carried out to assess the alternative role of high temperature tolerant plant growth promoting rhizobacteria (PGPR) in alleviation of heat stress adverse effect in eggplant.Methods: PGPR was assessed for PGP potentialities and investigated for1‐aminocyclopropane‐1‐carboxylate (ACC deaminase), and exopolysaccharide under normal and high temperature environment. The impact of PGPR application on plant physiology and biochemistry was investigated under normal and high temperature environments and plant growth regulators were evaluated using High Performance Liquid Chromatography (HPLC).Results: A significant impediment for morphological and physiological parameters of eggplant cultivars was observed during heat stress in absence of PGPR inoculation. The results showed that ACC‐deaminase produced by PGPR boosted up significantly the extracellular polymeric substances (EPS) accumulation, conversion of ACC into α‐ketobutyrate and ammonia, and reduce consequently the impact of high temperature on eggplant development.Conclusion: PGPR inoculation showed an alternative strategy to improve eggplant growth and development under high temperature condition in order to preserve agriculture sustainability and healthy crops.Keywords: ACC‐deaminase; Extracellular polymeric substances; Heat stress; PGPR; Solanum melongena

The interplay between the inoculation of plant growth-promoting rhizobacteria and the rhizosphere microbiome and their impact on plant phenotype

Microbial inoculation stands as a pivotal strategy, fostering symbiotic relationships between beneficial microorganisms and plants, thereby enhancing nutrient uptake, bolstering resilience against environmental stressors, and ultimately promoting healthier and more productive plant growth. However, while the advantageous roles of inoculants are widely acknowledged, the precise and nuanced impacts of inoculation on the intricate interactions of the rhizosphere microbiome remain significantly underexplored. This study explores the impact of bacterial inoculation on soil properties, plant growth, and the rhizosphere microbiome. By employing various bacterial strains and a synthetic community (SynCom) as inoculants in common bean plants, the bacterial and fungal communities in the rhizosphere were assessed through 16 S rRNA and ITS gene sequencing. Concurrently, soil chemical parameters, plant traits, and gene expression were evaluated. The findings revealed that bacterial inoculation generally decreased pH and V%, while increasing H+Al and m% in the rhizosphere. It also decreased gene expression in plants related to detoxification, photosynthesis, and defense mechanisms, while enhancing bacterial diversity in the rhizosphere, potentially benefiting plant health. Specific bacterial strains showed varied impacts on rhizosphere microbiome assembly, predominantly affecting rhizospheric bacteria more than fungi, indirectly influencing soil conditions and plants. Notably, Paenibacillus polymyxa inoculation improved plant nitrogen (by 5.2%) and iron levels (by 28.1%), whereas Bacillus cereus boosted mycorrhization rates (by 70%). Additionally, inoculation led to increased complexity in network interactions within the rhizosphere (∼15%), potentially impacting plant health. Overall, the findings highlight the significant impact of introducing bacteria to the rhizosphere, enhancing nutrient availability, microbial diversity, and fostering beneficial plant-microbe interactions.

Enhancing Native Plant Establishment in Mine Tailings under Drought Stress Conditions through the Application of Organo-Mineral Amendments and Microbial Inoculants

The implementation of phytoremediation strategies under arid and semiarid climates requires the use of appropriate plant species capable of withstanding multiple abiotic stresses. In this study, we assessed the combined effects of organo-mineral amendments and microbial inoculants on the chemical and biological properties of mine tailings, as well as on the growth of native plant species under drought stress conditions. Plants were cultivated in pots containing 1 kg of a mixture of mine tailings and topsoil (i.e., pre-mined superficial soil) in a 60:40 ratio, 6% marble sludge, and 10% sheep manure. Moreover, a consortium of four drought-resistant plant growth-promoting rhizobacteria (PGPR) was inoculated. Three irrigation levels were applied: well-watered, moderate water deficit, and severe water deficit, corresponding to 80%, 45%, and 30% of field capacity, respectively. The addition of topsoil and organo-mineral amendments to mine tailings significantly improved their chemical and biological properties, which were further enhanced by bacterial inoculation and plants’ establishment. Water stress negatively impacted enzymatic activities in amended tailings, resulting in a significant decrease in acid and alkaline phosphatases, urease, and dehydrogenase activities. Similar results were obtained for bacteria, fungi, and actinomycete abundance. PGPR inoculation positively influenced the availability of phosphorus, total nitrogen, and organic carbon, while it increased alkaline phosphatase, urease (by about 10%), and dehydrogenase activity (by 50%). The rhizosphere of Peganum harmala showed the highest enzymatic activity and number of culturable microorganisms, especially in inoculated treatments. Severe water deficit negatively affected plant growth, leading to a 40% reduction in the shoot biomass of both Atriplex halimus and Pennisetum setaceum compared to well-watered plants. P. harmala showed greater tolerance to water stress, evidenced by lower decreases observed in root and shoot length and dry weight compared to well-watered plants. The use of bioinoculants mitigated the negative effects of drought on P. harmala shoot biomass, resulting in an increase of up to 75% in the aerial biomass in plants exposed to severe water deficit. In conclusion, the results suggest that the combination of organo-mineral amendments, PGPR inoculation, and P. harmala represents a promising approach to enhance the phytoremediation of metal-polluted soils under semiarid conditions.

Comprehensive insights into sorghum (Sorghum bicolor) defense mechanisms unveiled: Plant growth-promoting rhizobacteria in combating Burkholderia-induced bacterial leaf stripe disease

Sorghum, a vital cereal crop with significant importance in traditional human health systems, faces severe challenges from biotic stresses. This study aimed to assess the morpho-physiological variations and plant growth promoting rhizobacteria (PGPR)-induced defense mechanisms in sorghum against Burkholderia sp. infection, a well-known cause of bacterial leaf stripe disease. Also, the alterations in the leaf protein band profile of sorghum exposed to Burkholderia infection were assessed via 2-D gel electrophoresis wherein the disappearance of protein bands in diseased leaf tissues was recorded. The selected PGPR, A. chroococcum Beijerinck 1901 (MCC 2351), B. megaterium (MCC 2336), and P. fluorescens (NAIMCC B-00,340), secreted hydrogen cyanide and ammonia, and produced lytic enzymes, cellulase and amylase. When tested in-planta, Burkholderia sp., applied as a foliar spray, more profoundly impacted the growth as compared to seed coat application, resulting in significant reductions in root dry biomass, whole plant length, and total chlorophyll content by 93.9, 73.4 and 53.8 %, respectively, compared to disease-free control. Visible symptoms of bacterial leaf stripe disease like brown discoloration and necrotic lesions were observed in infected sorghum plants. Furthermore, the level of phytochemicals, proline, and malondialdehyde and antioxidants, CAT and SOD, in foliage declined significantly by 46.4, 70.2, 20.7, and 16.9 %, respectively, following inoculation with Bacillus applied as a seed coat. Additionally, Burkholderia-infected plants exhibited cellular damage, mainly in leaf tissues, as revealed by SEM and CLSM. Interestingly, the PGPR inoculation substantially enhanced the measured growth parameters of sorghum while reducing the levels of phytochemicals and antioxidants. These findings suggest that A. chroococcum, B. megaterium, and P. fluorescens, possessing biocontrol activity, can be employed as a profitable, environment and pocket-friendly approach for managing plant diseases and promoting the production of sorghum under biotic stress, thereby sufficing the human food demands.

Paenibacillus lentimorbus alleviates nutrient deficiency-induced stress in Zea mays by modulating root system architecture, auxin signaling, and metabolic pathways.

Paenibacillus lentimorbus reprograms auxin signaling and metabolic pathways for modulating root system architecture to mitigate nutrient deficiency in maize crops. The arable land across the world is having deficiency and disproportionate nutrients, limiting crop productivity. In this study, the potential of plant growth-promoting rhizobacteria (PGPR) viz., Pseudomonas putida, Paenibacillus lentimorbus, and their consortium was explored for growth promotion in maize (Zea mays) under nutrient-deficient conditions. PGPR inoculation improved the overall health of plants under nutrient-deficient conditions. The PGPR inoculation significantly improved the root system architecture and also induced changes in root cortical aerenchyma. Based on plant growth and physiological parameters inoculation with P. lentimorbus performed better as compared to P. putida, consortium, and uninoculated control. Furthermore, expression of auxin signaling (rum1, rul1, lrp1, rtcs, rtcl) and root hair development (rth)-related genes modulated the root development process to improve nutrient acquisition and tolerance to nutrient-deficient conditions in P. lentimorbus inoculated maize plants. Further, GC-MS analysis indicated the involvement of metabolites including carbohydrates and organic acids due to the interaction between maize roots and P. lentimorbus under nutrient-deficient conditions. These findings affirm that P. lentimorbus enhance overall plant growth by modulating the root system of maize to provide better tolerance to nutrient-deficient condition.

Tripartite Introductions of PGPR, Humic Acid, and N-Fertilizer Improve the Growth and Yield of Sweet Potato Under Glasshouse Conditions

This study was undertaken to investigate the effects of plant growth-promoting rhizobacteria (PGPR) with humic acid (HA) as amendments on the morphological and physiological growth characteristics and yield of Sepang Oren sweet potato (Ipomoea batatas[L.] Lam). The experiment was conducted under glasshouse conditions at the Faculty of Agriculture, Universiti Putra Malaysia, for 110 days. Two factors were used in this experiment: The first factor was PGPR-HA inoculations (UPMB10, UPMRB9, and mixed strains) and non-inoculation-HA, and the second factor was the Nitrogen fertilizer levels (50, 75, and 100%). The treatments were replicated three times and arranged factorially in a randomized complete block design. The results showed that inoculations with PGPRs-HA (UPMRB9 and UPMB10 strains) positively affect the plant growth significantly (SPAD measurements, number of leaves, vine length, root length, leaf area index, root dry weight, shoot dry weight, and root: shoot ratio) of sweet potato upon addition of 50% and 75% of N-fertilizer, respectively. The nutrient content of soil and plant leaf significantly increased by 12-15% and 14-18%, respectively, compared to the uninoculated, when applied with the same inoculation. After 30 days, the population of soil bacteria increased, reaching a value of 8.65 log10 CFU/g soil. The use of PGPR-HA inoculations with N-fertilization resulted in a considerable rise in the majority of plant and soil parameters compared to the treatments without PGPR inoculation. Therefore, PGPR supplemented with humic acid (HA) may be considered a viable and sustainable strategy for enhancing sweet potatoes' morphological and physiological attributes. This technique can result in increased crop productivity and serve as a substitute for nitrogen-based fertilizers.

Plant-Growth-Promoting Rhizobacteria Modulate Carbohydrate Metabolism in Connection with Host Plant Defense Mechanism.

Plant-growth-promoting rhizobacteria (PGPR) could potentially enhance photosynthesis and benefit plant growth by improving soil nutrient uptake and affecting plant hormone balance. Several recent studies have unveiled a correlation between alterations in photosynthesis and host plant resistance levels. Photosynthesis provides materials and energy for plant growth and immune defense and affects defense-related signaling pathways. Photosynthetic organelles, which could be strengthened by PGPR inoculation, are key centers for defense signal biosynthesis and transmission. Although endophytic PGPRs metabolize plant photosynthates, they can increase soluble sugar levels and alternate sugar type and distribution. Soluble sugars clearly support plant growth and can act as secondary messengers under stressed conditions. Overall, carbohydrate metabolism modifications induced by PGPR may also play a key role in improving plant resistance. We provide a concise overview of current knowledge regarding PGPR-induced modulation in carbohydrate metabolism under both pathogen-infected and pathogen-free conditions. We highlight PGPR application as a cost-saving strategy amidst unpredictable pathogen pressures.

Growth and protein response of rice plant with plant growth-promoting rhizobacteria inoculations under salt stress conditions.

Soil salinity has been one of the significant barriers to improving rice production and quality. According to reports, Bacillus spp. can be utilized to boost plant development in saline soil, although the molecular mechanisms behind the interaction of microbes towards salt stress are not fully known. Variations in rice plant protein expression in response to salt stress and plant growth-promoting rhizobacteria (PGPR) inoculations were investigated using a proteomic method and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Findings revealed that 54 salt-responsive proteins were identified by mass spectrometry analysis (LC-MS/MS) with the Bacillus spp. interaction, and the proteins were functionally classified as gene ontology. The initial study showed that all proteins were labeled by mass spectrometry analysis (LC-MS/MS) with Bacillus spp. interaction; the proteins were functionally classified into six groups. Approximately 18 identified proteins (up-regulated, 13; down-regulated, 5) were involved in the photosynthetic process. An increase in the expression of eight up-regulated and two down-regulated proteins in protein synthesis known as chaperones, such as the 60kDa chaperonin, the 70kDa heat shock protein BIP, and calreticulin, was involved in rice plant stress tolerance. Several proteins involved in protein metabolism and signaling pathways also experienced significant changes in their expression. The results revealed that phytohormones regulated the manifestation of various chaperones and protein abundance and that protein synthesis played a significant role in regulating salt stress. This study also described how chaperones regulate rice salt stress, their different subcellular localizations, and the activity of chaperones.

Halotolerant Rhizobacteria Promote Plant Growth and Decrease Salt Stress in Carya illinoinensis (Wangenh.) K. Koch

Pecan cultivation holds significant global importance. Salinity negatively affects the physiology and metabolism of the plant. However, certain plant growth-promoting rhizobacteria (PGPR) have the ability to reduce salt stress in plants. The objective was to analyze the effects of the rhizobacteria Bacillus paralicheniformis strain LBEndo1 on the development of pecan seedlings under salinity stress conditions. Two factors were analyzed: the presence of saline stress and the bacterial inoculation. The bacterial application was conducted at a concentration of 1 × 108 CFU/mL, and irrigation was administered every third day with 80 mL of water containing 50 mM NaCl. The results show that the rhizobacteria has a maximum tolerance of 15% salinity. Furthermore, the inoculation of PGPR significantly increased the biomass of the seedlings, including the dry weight of leaves, stem, and roots, as well as the stem diameter and height. Furthermore, seedlings that interacted with the rhizobacteria exhibited superior development under saline conditions, with significant increases of 105.5% in chlorophyll concentration and 112% in proline accumulation compared to non-inoculated seedlings. Additionally, a remarkable reduction in leaf damage caused by salt stress was observed. In conclusion, the LBEndo1 rhizobacteria, being a strain resistant to salinity and possessing multiple mechanisms to promote growth while mitigating salt stress, has the potential to be utilized in pecan seedlings to alleviate stress caused by salinity and increases biomass.

Application of rhizobacteria to improve microbial community structure and maize (Zea mays L.) growth in saline soil.

The utilization of plant growth-promoting rhizobacteria (PGPR) has emerged as a prominent focus in contemporary research on soil microbiology, microecology, and plant stress tolerance. However, how PGPR influence the soil bacterial community and related ecological functions remains unclear. The aim of this study was to investigate the effects of three natural PGPR inoculations (YL07, Planococcus soli WZYH02; YL10, Bacillus atrophaeus WZYH01; YL0710, Planococcus soli WZYH02 and Bacillus atrophaeus WZYH01) on maize (Zea mays L.) growth under two salt stress conditions (S1, ECe = 2.1 ~ 2.5 dS/m; S2, ECe = 5.5 ~ 5.9 dS/m). The results revealed that compared to the control (CK), the average plant height of maize seedlings significantly increased by 27%, 23%, and 29% with YL07, YL10, and YL0710 inoculation under S1 conditions, respectively, and increased by 30%, 20%, and 18% under S2 conditions, respectively. Moreover, PGPR inoculation positively influenced the content of superoxide dismutase, catalase, soluble sugar, and proline in maize under salt stress. Subsequent analysis of alpha diversity indices, relative microbial abundance, principal coordinate analysis, cladograms, and linear discriminant analysis effect size histograms indicated significant alterations in the rhizosphere microbial community due to PGPR inoculation. FAPROTAX analysis demonstrated that YL10 inoculation in S2 rhizosphere soil had a notable impact on carbon cycle functions, specifically chemoheterotrophy, fermentation, and phototrophy. Thus, this study provides evidence that PGPR inoculation improves soil microbial communities and plant indices under salt stress. These findings shed light on the potential of PGPR as a viable approach for enhancing plant stress tolerance and fostering sustainable agricultural practices.

Transcriptome analysis of growth and quality response of chrysanthemum to co-inoculation with Bacillus velezensis and Pseudomonas aeruginosa

The inoculation of plants with plant growth-promoting rhizobacteria (PGPR) has been increasingly discussed as a way to sustainably promote plant growth and soil health. Although some promising results have been achieved in the laboratory, the applications of microbial inoculants in chrysanthemum production greenhouses and co-inoculation with PGPRs in ornamental planting systems have been less investigated. Here, greenhouse experiments were conducted to study the integrated effect of bioagents (Bacillus velezensis and Pseudomonas aeruginosa) on chrysanthemum nutrient use efficiency, plant growth, and quality. The growth-promoting mechanisms were further elucidated by transcriptome analysis. Co-inoculation with the two PGPRs increased the absorption and utilization of nitrogen, phosphorus, and potassium. The quality and growth of chrysanthemum were significantly higher than those of single PGPR inoculation or soil conditioner application. Transcriptome analysis revealed that differentially expressed genes (DEGs) were co-expressed at 30, 60, and 90 days after chrysanthemum co-inoculation with the two PGPRs. DEGs were primarily enriched in metabolic and signal transduction pathways. PDC encoding pyruvate decarboxylase in the glycolysis pathway and SAUR32 and SAUR36 encoding auxin were upregulated in chrysanthemum during the PGPRs inoculation period. Notably, the transcription factors WRKY70 and BHLH35 belonging to signal transduction and defense responses were both upregulated, demonstrating that chrysanthemum system and disease resistance were activated. The results of this study could help to elucidate the mechanism of 2 PGPRs on chrysanthemum growth and development at the transcriptome level, which could lay a theoretical foundation for the highly efficient cultivation of cut chrysanthemum “Qinhuai Yulian”.

Phytoremediation technology for recovery of Ni by Acacia plants in association with Bacillus amyloliquefaciens isolated from E-waste contaminated site

Electronic waste (e-waste) illegally disposal in Thailand is becoming more widespread. A sustainable metal recovery technology is needed. A phytotechnology called “phytomining” of metals such as nickel (Ni) is a promising technology providing a sustainable solution to the growing e-waste problems. This study investigated the ability of Acacia species in association with e-waste site isolated, plant growth-promoting rhizobacteria (PGPR), Bacillus amyloliquefaciens. Acacia mangium accumulated higher Ni in their tissues when Ni concentrations in soil were lower than 200 mg kg−1. The inoculation of PGPR B. amyloliquefaciens enhanced Ni uptake and accumulation in the leaves, stem, and root. The results showed that the highest Ni concentration was found in the root ash (825.50 mg kg−1) when inoculated plants were grown in soil containing 600 mg kg−1 Ni. Hence, the Ni recovery process and mass balance were performed on root ashes. The highest Ni recovery was 91.3% from the acid (H2SO4) leachate of the ash of inoculated plant treated with 600 mg kg−1 Ni. This demonstrates the feasibility of PGPR-assisted phytomining from Ni-contaminated soil. Phytomining of Ni from any e-waste contaminated sites using Acacia mangium in combination with B. amyloliquefaciens can promote plant growth and improve the uptake of Ni.

Inoculation with plant growth-promoting rhizobacteria improves seagrass Thalassia hemprichii photosynthesis performance and shifts rhizosphere microbiome

Plant growth-promoting rhizobacteria (PGPR) inoculation is a crucial strategy for maintaining the sustainability of agriculture and presents a promising solution for seagrass ecological restoration in the face of disturbances. However, the possible roles and functions of PGPRs in the seagrass rhizosphere remain unclear. Here, we isolated rhizosphere bacterial strains from both reef and coastal regions and screened two PGPR isolates regarding their in vivo functional traits. Subsequently, we conducted microcosm experiments to elucidate how PGPR inoculation affected seagrass photosynthesis and shape within each rhizosphere microbiome. Both screened PGPR strains, Raoultella terrigena NXT28 and Bacillus aryabhattai XT37, excelled at expressing a specific subset of plant-beneficial functions and increased the photosynthetic rates of the seagrass host. PGPR inoculation not only decreased the abundance of sulfur-cycling bacteria, it also improved the abundance of putative iron-cycling bacteria in the seagrass rhizosphere. Strain XT37 successfully colonized the seagrass rhizosphere and displayed a leading role in microbial network structure. As a nitrogen-fixing bacteria, NXT28 showed potential to change the microbial nitrogen cycle with denitrification in the rhizosphere and alter dissimilatory and assimilatory nitrate reduction in bulk sediment. These findings have implications for the development of eco-friendly strategies aimed at exploiting microbial communities to confer sulfide tolerance in coastal seagrass ecosystem.

Characterization and utilization of multi-trait plant growth promoting rhizobacteria from arid soils of western Rajasthan for enhancing drought resilience in an arid legume

In the study, plant growth promoting rhizobacteria (PGPR) indigenous to arid western Rajasthan were isolated and screened for plant growth promoting (PGP) capabilities. Ten isolates showing multiple PGP activities were identified as Pseudomonas sp. G6-3, Staphylococcus sp. G6-4, Bacillus badius G8-6, Agrobacterium sp. G8-7, Bacillus pseudomycoides G10-1, Staphylococcus capitis subsp. capitis G11-4, Bacillus paralicheniformis G11-5, Bacillus subtilis G12-3, Stenotrophomonas pavanii G12-4, and Solibacillus isronensis G21-9. Physiological profiling of these isolates demonstrated them to be tolerant to drought (25% PEG-6000), high temperature (40 °C), alkalinity (pH 10.0), and salinity (4.5% NaCl). These PGPR significantly improved clusterbean seedling characteristics in moisture stress-induced hydroponic flask cultures and pots. PGPR inoculation of clusterbean in drought-induced pots significantly enhanced the plant dry weight by 15–33%, plant water potential by 5–8%, and the relative water content of leaves by 4–16%. There was also a significant reduction in the levels of anti-oxidant enzymes and proline in plant tissues under drought conditions, which indicated lower levels of stress experienced by the treated plants. These were translated into yield enhancements by 13–15% under rainfed conditions. The study demonstrates the ability of stress tolerant PGPR from arid western Rajasthan in enhancing drought resilience of arid legumes besides promoting their growth, and their potential utility in sustainable arid agriculture systems.

PGPR-Soil Microbial Communities' Interactions and Their Influence on Wheat Growth Promotion and Resistance Induction against Mycosphaerella graminicola.

The efficiency of plant-growth-promoting rhizobacteria (PGPR) may not be consistently maintained under field conditions due to the influence of soil microbial communities. The present study aims to investigate their impact on three PGPR-based biofertilizers in wheat. We used the PGPR Paenibacillus sp. strain B2 (PB2), PB2 in co-inoculation with Arthrobacter agilis 4042 (Mix 2), or with Arthrobacter sp. SSM-004 and Microbacterium sp. SSM-001 (Mix 3). Inoculation of PB2, Mix 2, and Mix 3 into non-sterile field soil had a positive effect on root and aboveground dry biomass, depending on the wheat cultivar. The efficiency of the PGPR was further confirmed by the protection they provided against Mycosphaerella graminicola, the causal agent of Septoria leaf blotch disease. PB2 exhibited protection of ≥37.8%, while Mix 2 showed ≥47.9% protection in the four cultivars tested. These results suggest that the interactions between PGPR and native soil microbial communities are crucial for promoting wheat growth and protection. Additionally, high-throughput sequencing of microbial communities conducted 7 days after PGPR inoculations revealed no negative effects of PB2, Mix 2, and Mix 3 on the soil microbial community structure. Interestingly, the presence of Arthrobacter spp. appeared to mitigate the potential negative effect of PB2 on bacterial community and foster root colonization by other beneficial bacterial strains.