Plant Growth-promoting Rhizobacteria Research Articles

Mitigating negative impacts of drought on oak seedlings performances through plant growth-promoting rhizobacteria.

Drought stress during the plant's growing season is a serious constraint to plant establishment in arid and semiarid Mediterranean ecosystems. Plant growth promoting rhizobacteria (PGPR) as environmentally friendly and innovative management approach can be used to produce seedlings better adapted to these environments. We tested native PGPR strains isolated from drought-tolerant tree and shrub species originating from two climatically contrasting regions: hot-dry (Dehloran) and milder Mediterranean climate (Ilam). These strains were used as a biological input to improve the morphological and physiological traits of Brant's oak (Quercus brantii Lindl.) seedlings in a greenhouse experiment. Seedlings were inoculated with various drought-tolerant strains or a combination of all bacteria (Bmix) and their morpho-physiological traits were measured under three levels of water stress (80% field capacity, FC80: no stress; 60% FC, FC60: moderate water stress and 40% FC, FC40: severe water stress). Strains from Dehloran were the most performant (Bacillus anthracis, B. licheniformis, B. cereus) except Stenotrophomonas maltophilia which originated from Ilam. They demonstrated the ability to solubilize insoluble phosphates (except for the B. licheniformis). They were also all able to produce auxin and the ACC-deaminase enzyme (except S. maltophilia). PGPR application, water stress treatments, and their interaction significantly influenced all the morphological and physiological seedling traits. Most traits significantly (p<0.01) decreased under FC40, in particular average leaf area, shoot fresh weight, and shoot dry weight. This decrease was particularly marked for the control (no inoculation), as the leaf area was reduced by 60% in FC40. In FC40, all bacterial treatments, especially B. cereus and Bmix efficiently improved seedling morphological traits and seedling quality index. The highest amount of chlorophyll a in FC40 was recorded for Bmix and B. licheniformis isolates. Total phenolic content and malondialdehyde levels, as well as proline, showed an increase under water stress conditions, particularly at FC40, irrespective of inoculation conditions. The amounts of malondialdehyde without inoculation increased significantly under water stress and the content were 1.3 and 2 times higher in FC60 and FC40, respectively, compared to FC80 with no inoculation. Under water stress, seedling performances and quality were impacted and the production of substances associated with physiological defense mechanisms, increased. However, the application of PGPR was able to mitigate these effects (in particular for B. cereus and Bmix). We concluded that application of drought tolerant PGPRs can be a cost effective and ecologically sustainable method for producing oak seedlings better adapted to water-scarce environments.

Broad-spectrum applications of plant growth-promoting rhizobacteria (PGPR) across diverse crops and intricate planting systems.

Multifunctional plant growth-promoting rhizobacteria (PGPR) have garnered significant attention in agricultural applications; however, a few have applied them in crop rotation or intercropping fields. To identify PGPR with strong colonization ability and broad spectrum benefit, we screened strains from the local tobacco rhizosphere and evaluated their growth-promoting effects across various crops and farming systems. In this study, strain L8, identified as Bacillus thuringiensis, was selected as a multifunctional PGPR capable of producing indole-3-acetic acid (IAA), solubilizing potassium, and mobilizing both organic and inorganic phosphorus. Compared with the control group, the soil treated with strain L8 in tobacco pot experiments showed significantly higher levels of IAA, available potassium, and available phosphorus. Furthermore, tobacco plants inoculated with L8 exhibited significantly improved growth parameters compared with the uninoculated control. The results indicated that compared with the control, strain L8 increased tobacco fresh weight (by 83.18%), plant height (by 29.32%), relative chlorophyll content (by 14.33%), as well as plant phosphorus (by 23.78%) and potassium (by 30.81%). Interestingly, L8 not only enhanced tobacco growth but also improved tobacco root morphology, significantly increasing root length (1.55-fold), root surface area (1.78-fold), and root volume (2.05-fold) compared with the control. These findings provide valuable insights into utilizing plant growth-promoting bacteria for tobacco production. Moreover, the inoculation strain L8 enriched soil organic matter and nutrient content in both wheat (Triticum aestivum)-maize (Zea mays) rotation and peanut (Arachis hypogaea)-maize intercropping systems. Furthermore, within the intricate tillage systems of wheat-corn rotation and peanut-corn intercropping, multifunctional PGPR strain L8 can play a crucial role in crop growth promotion, yield increase, and higher soil nutrient availability.IMPORTANCEThese findings aim to study the application of plant growth-promoting rhizobacteria (PGPR) in diverse crops and complex planting systems, showing their adaptability and effectiveness in various agricultural contexts. The study suggests that this strain improves nutrient utilization in the soil, enhances soil health, and plays a significant role in plant growth through the secretion of substances like auxin (IAA). In parallel, we observed that applying this strain improved the production efficiency of wheat, corn, and peanuts within complex farming systems, indicating that this method holds the potential for enhancing both the yield and quality of various crops.

Co-inoculation with Bacillus thuringiensis RZ2MS9 and rhizobia improves the soybean development and modulates soil functional diversity.

Despite the beneficial effects of Plant Growth-Promoting Rhizobacteria (PGPR) on agriculture, understanding the consequences of introducing foreign microbes into soil taxonomic and functional diversity is necessary. This study evaluated the effects co-inoculation of soybean with Bacillus thuringiensis (Bt) RZ2MS9 and commercial rhizobia on the natural microbial community structure and functional potential. Our results indicated that soybean development was positively influenced by co-inoculation, plants exhibited greater height and a higher number of pods, and no reductions in productivity estimates. Soil prokaryotic diversity and community structure remained unchanged by Bt RZMS9 inoculation or co-inoculation with rhizobia 147 Days After Sowing (DAS). However, functional diversity was influenced by sole Bt inoculation, potentially due to community quorum sensing disruption by N-acyl homoserine lactone hydrolases. The genes enriched by co-inoculation were mostly related to soil phosphorus cycling, with gcd showing the most pronounced increase. The nifA genes increased when rhizobia alone were inoculated, suggesting that this pathway could be affected by Bt RZ2MS9 inoculation. This study demonstrates the synergistic activity of rhizobia and Bt RZ2MS9 on soybean development, without significantly interfering with natural microbial community, presenting a promising approach for sustainable crop management.

The Isolation of Lead-Tolerant PGPR from Red Clover Soil and Its Role in Promoting the Growth of Alfalfa.

Alfalfa (Medicago sativa L.) is an outstanding species used for the remediation of heavy metal-contaminated soil, and our previous research has shown that PGPR can promote plant growth under high-concentration lead stress. This discovery has forced scientists to search for PGPR strains compatible with alfalfa to develop an innovative bioremediation strategy for the remediation of lead-contaminated soil. This study used lead-tolerant rhizosphere soil of red clover as experimental material; cultured, isolated, and screened 52 excellent lead-tolerant bacteria that promote rhizosphere growth; and then inoculated them into alfalfa. Marked differences existed in the secretion of auxin, protease, and ACC deaminase among these strains. The results indicated that Pseudomonas spp. (strain Y2), Pseudomonas spp. (strain Y22), and Bacillus spp. (strain Y23) exhibited a strong growth-promoting ability in alfalfa, and there was no antagonistic reaction among the three strains, enabling their coexistence. The pot experiment manifested that strains Y2, Y22, Y23, and YH (a mixture of Y2, Y22, and Y23) could increase the plant height, root length, fresh and dry weight above ground, and fresh and dry weight below ground of alfalfa. They could all significantly raise the chlorophyll content and antioxidant enzyme activity in alfalfa (p < 0.05) and the content of malondialdehyde (MDA) in alfalfa. Furthermore, the concurrent inoculation of three distinct types of plant growth-promoting rhizobacteria (PGPR) significantly diminished lead (Pb) concentrations in rhizosphere soil, enhanced the levels of available potassium (AK) and available phosphorus (AP), and augmented the capacity of plants to absorb Pb. The results imply that PGPR can be employed to facilitate plant growth and microbial-assisted remediation of lead and other heavy metal-contaminated soil and establish a basis for further research on the growth-promoting mechanism of PGPR in plants.

Development, Shelf Stability, and In-Vitro Evaluation of Liquid Bacterial Inoculant Acinetobacter lwoffii Strain PAU_31LN.

Acinetobacter has been recognized as a versatile plant growth promoting (PGP) rhizobacteria (PGPR) that produce multiple PGP traits. The present study was conducted to formulate an efficient and stable liquid bacterial inoculant (LBI) of Acinetobacter lwoffii strain PAU_31LN. In the current investigation, total 16 endophytic bacteria were isolated from cotton leaves and evaluated for plant growth-promoting features such as production of phytohormones, mineral solubilization, siderophore production, hydrogen cyanide (HCN) production, and 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity. The leaf endophytic bacteria designated as 31LN was found promising for all the PGP traits and it was identified as A. lwoffii strain PAU_31LN by 16S rRNA gene sequencing. For the development of LBI of A. lwoffii strain PAU_31LN, 4.5 g/L yeast extract, 5 g/L NaCl, 5 g/L peptone, and 12.5 mM food-grade trehalose was optimized as appropriate medium composition using response surface methodology (RSM) and Box-Behnken design. Further, the viability of A. lwoffii strain PAU_31LN in the optimized formulation was observed as 1.1 folds higher over the control after 180 days of storage at room temperature. Moreover, nonsignificant variation was recorded in the functional traits of 180 days old LBI of A. lwoffii strain PAU_31LN and freshly prepared LBI. The in-vitro plant growth parameters such as length and seed vigor index of 7-day-old cotton seedlings were enhanced by the seed bio-priming with LBI of A. lwoffii strain PAU_31LN over the control. The results of the present study signify the importance of endophytes and statistical methods to formulate prominent LBI.

Cell-free supernatants from plant growth-promoting rhizobacteria Bacillus albus strains control Aspergillus flavus disease in peanut and maize seedlings

BackgroundAspergillus flavus, a seed-borne fungal pathogen, colonizes host plants and exploits nutrients, hindering the growth of seedlings such as peanut and maize. This study investigates the effectiveness of cell-free supernatants (CFSs) from the plant growth-promoting rhizobacteria (PGPR) Bacillus albus strains NNK24 and NDP61, which belong to the Bacillus cereus group, in suppressing A. flavus AF1.ResultsThe antifungal activity of these CFSs was attributed to their surfactant properties and chemical composition. These were characterized using rapid chemical assays and ultra-high-performance liquid chromatography-electrospray ionization-quadrupole time-of-flight/mass spectrometry (UHPLC-ESI-QTOF/MS), combined with bioinformatic tools such as Global Natural Product Social Molecular Networking (GNPS) and Natural Products Atlas (NPAtlas). Identified putative antifungal compounds included two diketopiperazines (cyclo(Pro-Leu) and cyclo(2-hydroxy-Pro-Leu)), four macrolactins (7-O-succinyl macrolactin A, 7-O-methyl-5′-hydroxy-3′-heptenoate-macrolactin, macrolactin B, and macrolactin C), two siderophores (petrobactin and bacillibactin), and three cyclic lipopeptides (kurstakin 1, 2 or 3, and 4). These compounds are hypothesized to act synergistically via multiple mechanisms, including disruption of fungal membranes, iron capture, direct antibiosis, and triggering plant immunity. Both CFSs strongly suppressed the harmful effects of A. flavus AF1 and seed-borne A. flavus on peanut and maize seedlings, reducing disease incidence (DI) and disease severity index (DSI) compared to controls. The disease control efficacy (DCE) of the CFSs was comparable to that of the commercial fungicide. Additionally, the CFSs enhanced seed germination, vigor, seedling length, and weight in both peanut and maize. Vigor index (VI) values increased by 222.4–286.0% in peanuts and 181.7–216.4% in maize at 7 days after treatment (DAT).ConclusionCFSs of B. albus NNK24 and NDP61 show significant potential as bioprotective agents for sustainable agriculture. Importantly, their use eliminates the need for live bacterial cells from the B. cereus group, addressing biosafety concerns.Graphical abstract

Identification and functional characterization of a fructose-inducible phosphotransferase system in Azospirillum brasilense Sp7.

Plant growth-promoting rhizobacterium Azospirillum brasilense Sp7 utilizes fructose efficiently via a fructose phosphotransferase system (Fru-PTS). Its genome encodes two putative Fru-PTS, each consisting of FruB (EIIA), FruK (Pfk), and FruA (EIIBC) proteins. We compared the proteomes of A. brasilense Sp7 grown with malate or fructose as sole carbon source, and noticed upregulation of the constituent proteins of Fru-PTS1 only on fructose. Inactivation of fruA gene of both the Fru-PTS showed that Fru-PTS1 is the main PTS involved in fructose utilization. Overexpression of fruA1 in A. brasilense Sp7 enhanced its growth on fructose showing improved consumption of fructose. This suggested that fructose utilization in A. brasilense Sp7 is limited due to the limitation of EIIBC component. A FruR-type regulator, encoded divergently to the Fru-PTS1 operon, was required for chemotaxis toward fructose. Although not an absolute necessity for the growth of fructose, FruR was required for the optimal growth of fructose. The fruB1 promoter was activated by fructose and repressed by malate, but FruR does not seem to regulate its expression. A 27-nucleotide stem-loop structure located between the -125 and -99 promoter proximal region of fruB1 was involved in fructose inducibility and malate repression. Fructose also upregulated several proteins involved in the biogenesis of a Type 6 secretion system. Here, we have shown that A. brasilense Sp7 was able to inhibit the growth of Escherichia coli and Agrobacterium tumefaciens in the presence of fructose, and that an intact T6SS was required for contact-dependent growth inhibition of the two Gram-negative bacteria.IMPORTANCEAzospirillum brasilense, a plant growth-promoting rhizobacterium, has limited ability to utilize carbohydrates and sugars. Although it is known to utilize fructose via a fructose phosphotransferase system (fructose-PTS), the genes involved in fructose utilization and the role of fructose in its biology were not well characterized. This study has shown that out of the two units of fructose-PTS encoded in its genome, fructose-PTS1 plays the major role in fructose utilization. Overexpression of the membrane component (EIIBC) improved the growth of A. brasilense on fructose. The ability of fructose to induce proteins of the Type 6 Secretion System (T6SS) enables A. brasilense to cause contact-dependent inhibition of the growth of Escherichia coli as well as A. tumefaciens. This is the first report on the fructose inducibility of T6SS in A. brasilense, which may provide a handle to control the growth of undesirable bacteria using T6SS of A. brasilense in a mixed culture.

Exploring the efficacy of drought tolerant, IAA-producing plant growth-promoting rhizobacteria for sustainable agriculture

ABSTRACT The growing human population and abiotic stresses pose significant threats to food security, with PGPR favorable as biofertilizers for plant growth and stress relief. In one study, soil samples from both cultivated and uncultivated plants in various cities were used to isolate rhizobacterial populations. Using 50 soil samples from both cultivated and uncultivated plants, isolated rhizobacterial populations were screened for various biochemical changes, PGP activities and morphological characteristics. A total of 199 rhizobacteria were isolated and screened for IAA production. The strain M28 produced maximum IAA 378.44 ± 2.5 µg ml−1, M9 formed only 34.72 ± 0.15 µg ml−1. About 19% of IAA producers were isolated from Multan, 18% Lahore, 15% from soils of Faisalabad and Sheikhupura, while 7% from Gujrat. The 21 isolates were drought tolerant to −0.14Mpa, 14 of those were PSB and 15 were N fixers. In PGP traits, maximum zinc solubility was expressed by M4 as 2 ± 0.5 cm of zone. The strain M22 produced amount of HCN, 40.12 ± 0.052 ppm. All isolates showed diverse behavior in biocompatibility, motility patterns and hydrophobicity. Selected drought tolerant strains were genetically identified by ribotyping. Multitrait PGPR could be effective biofertilizers rather than with single trait. The strain M28 having highest production of IAA, was gelatinase, methyl red positive and was also capable of nitrogen fixation. Moreover, it had maximum swimming (8.9 mm) and swarming (8.7 mm) activities after 24 h, indicating its best PGP traits for future use.

Unlocking olive rhizobacteria: harnessing biocontrol power to combat olive root rot and promote plant growth.

Olive trees are susceptible to various diseases, notably root rot caused by Pythium spp., which presents significant challenges to cultivation. Conventional chemical control methods have limitations, necessitating exploration of eco-friendly alternatives like biological control strategies. This study aims to evaluate the potential of rhizobacteria in managing Pythium schmitthenneri-induced root rot in olive trees. We screened 140 bacteria isolated from olive tree rhizospheres for antifungal activity against the pathogen in vitro. Twelve isolates exhibited promising antifungal activity, identified through 16S rDNA gene sequencing as primarily Bacillus, Pseudomonas, Stenotrophomonas, and Alcaligenes species. Particularly, Pseudomonas koreensis (A28 and A29), Pseudomonas reinekei (A16), and Bacillus halotolerans (A10) were the highest effective strains. Mechanistic investigations revealed positive protease production in all twelve isolates, with eight producing amylase and cellulase. Chitinase activity was absent, while five solubilized tricalcium phosphate. Furthermore, eight secreted hydrocyanic acid (HCN), ten synthesized indole-3-acetic acid (IAA), and nine produced siderophores. Variability existed in antimicrobial substance production, including bacillomycin (seven isolates), iturin (eleven isolates), fengycin (two isolates), and surfactin (three isolates). Plant growth-promoting rhizobacteria (PGPR) capabilities were assessed using canola (Brassica napus) seedlings, showing enhanced growth in treated seedlings compared to controls. Greenhouse experiments confirmed the biocontrol efficacy of P. koreensis A28 and Bacillus subtilis C6 against root rot disease. These findings suggest these strains could serve as promising tools for managing olive tree root rot, offering a sustainable alternative to hazardous agrochemicals.

Impact of aeration on plant growth-promoting rhizobacteria assisted phytoremediation capability of arsenic in artificial wetland system.

The increasing demand for sustainable, robust, and cost-efficient arsenic (As) treatment techniques strengthens the implementation of new constructed wetland (CW) designs like aerated CWs in the agricultural sector. The aim was to assess and contrast the influence of various aeration rates on As elimination in subsurface flow CW utilizing Pennisetum purpureum plants for treating As-polluted sand. This study consisted of an experiment with 16 subsurface flow CW, operating at different As concentrations of 0, 5, 22, and 39 mgkg-1 and aeration rates of 0, 0.18, 1, and 2 Lmin-1. The highest elimination of As from treatment sand in the subsurface flow CWs was 96.19±3.09%, 93.95±2.17%, and 91.91±1.92% for 5, 22, and 39 mgkg-1 As, respectively, at 0.18 Lmin-1 aeration. A negative influence of As pollution on growth was detected in the 0, 1, and 2 Lmin-1 aeration but Pennisetum purpureum grows well in polluted sand with 0.18 Lmin-1 aeration. Bacterial population and different enzyme activity showed statistically significant differences with 0, 0.18, 1, and 2 Lmin-1 aerations at all As levels. These results suggest that this treatment can be used for As phytoremediation in anthropogenically polluted environments due to its high capability to uptake As.

Efficacy of the Plant Growth Promoting Rhizobacterium and Lufenuron for Reducing Insect-associated Yield Losses in Cauliflower

Insect attacks on plants are a severe problem in the agricultural sector. The damages caused by insects have an adverse impact on plant growth which leads to slow economic growth, particularly in countries dependent on agriculture. Plant growth-promoting rhizobacteria (PGPR) are widely utilized in agriculture because they offer a viable alternative to pesticides and artificial fertilizers. The growth and life cycle of insects/pests is inhibited by the insect growth regulators (IGRs), which belong to third-generation insecticides. Lufenuron is an IGR having a broad-spectrum insecticidal activity. Lufenuron inhibits insect growth by reducing chitin synthesis. A field experiment was carried out at Ayyub Agricultural Research Institute, Faisalabad, to evaluate the effect of MUR-4 (a potential PGRP) and lufenuron on cauliflower under insect attack. Cauliflower (Naran F1) seedlings were grown with and without a potential PGPR (MUR-4) using a randomized complete block design (RCBD). Attacks of cutworms, diamondback moths, armyworms and aphids were recorded periodically. Lufenuron was applied as a foliar spray, to inoculated as well as non-inoculated plants, upon insect attack. A foliar spray of lufenuron exerted a positive effect and reduced the insect attack. Plant biochemical analysis manifested the higher activities of phenolics and proline (secondary metabolites) in MUR-4 PGPR inoculated plants. Increased levels of malondialdehyde (MDA) and H2O2 indicated oxidative stress in plants. Peroxidase (POD), catalase (CAT) and superoxide dismutase (SOD) enzymes play a very important role in defence against insect-induced biotic stress. MUR-4 PGPR inoculation enhanced the activity of the mentioned enzymes i.e. POD, CAT and SOD. We concluded that lufenuron spray can positively assist farmers in insect control strategies. Furthermore, MUR-4 PGPR inoculation improved the plant defence system against insect herbivory.

Cu-tolerant Klebsiella variicola SRB-4 increased the nanoparticle (NP) stress resilience in garden peas (Pisum sativum L.) raised in soil polluted with varying doses of copper oxide (CuO)-NP.

Utilizing metal/nanoparticle (NP)- tolerant plant growth-promoting rhizobacteria (PGPR) is a sustainable and eco-friendly approach for remediation of NP-induced phytotoxicity. Here, Pisum sativum (L.) plants co-cultivated with different CuO-NP concentrations exhibited reduced growth, leaf pigments, yield attributes, and increased oxidative stress levels. Cu-tolerant (800µM) Klebsiella variicola strain SRB-4 (Accession no. OR715781.1) recovered from metal-contaminated soils produced various PGP traits, including IAA, EPS, siderophore, HCN, ammonia, and solubilized insoluble P. The PGP substances were marginally increased with increasing CuO-NP concentrations. When applied, Cu-tolerant SRB-4 strain increased root length (18%), root biomass (15.3%), total chlorophyll (29%), carotenoids (30%), root N (21%), root P (23%), total soluble protein (20%) nodule number (32%), nodule biomass (39%) and leghaemoglobin content (18%) in 50µM CuO-NP-exposed peas. Furthermore, proline, malondialdehyde (MDA), superoxide radical, hydrogen peroxide (H2O2) content, and membrane injury in K. variicola-inoculated and 50µM CuO-NP-treated plants were maximally and significantly (p ≤ 0.05) reduced by 70.6, 26.8, 60.8, and 71.6%, respectively, over uninoculated but treated with similar NP doses. Moreover, K. variicola inoculation caused a significant (p ≤ 0.05) decline in Cu uptake in roots (71%), shoots (65.5%), and grains (76.4%) of peas grown in soil contaminated with 50µM CuO-NP. The multivariate i.e. heat map and pearson correlation analyses between the NP-treated and PGPR inoculated parameters revealed a significant and strong positive corelation. The NP-tolerant indigenous beneficial K. variicola could be applied as an alternative to enhance the production of P. sativum cultivated in nano-polluted soil systems. Additionally, more investigation is required to ascertain the seed/soil inoculation effect of K. variicola SRB-4 on soil biological activities and different crops under various experimental setups.

Combined Transcriptomics and Metabolomics Uncover the Potential Mechanism of Plant Growth-Promoting Rhizobacteria on the Regrowth of Leymus chinensis After Mowing.

Mowing significantly influences nutrient cycling and stimulates metabolic adjustments in plants to promote regrowth. Plant growth-promoting rhizobacteria (PGPR) are crucial for enhancing plant growth, nutrient absorption, and stress resilience; however, whether inoculation with PGPR after mowing can enhance plant regrowth capacity further, as well as its specific regulatory mechanisms, remains unexplored. In this study, PGPR Pantoea eucalyptus (B13) was inoculated into mowed Leymus chinensis to evaluate its effects on phenotypic traits, root nutrient contents, and hormone levels during the regrowth process and to further explore its role in the regrowth of L. chinensis after mowing. The results showed that after mowing, root nutrient and sugar contents decreased significantly, while the signal pathways related to stress hormones were activated. This indicates that after mowing, root resources tend to sacrifice a part of growth and prioritize defense. After mowing, B13 inoculation regulated the plant's internal hormone balance by reducing the levels and signal of JA, SA, and ABA and upregulated the signal transduction of growth hormones in the root, thus optimizing growth and defense in a mowing environment. Transcriptomic and metabolomic analyses indicated that B13 promoted nutrient uptake and transport in L. chinensis root, maintained hormone homeostasis, enhanced metabolic pathways related to carbohydrates, energy, and amino acid metabolism to cope with mowing stress, and promoted root growth and regeneration of shoot. This study reveals the regenerative strategy regulated by B13 in perennial forage grasses, helping optimize resource utilization, increase yield, and enhance grassland stability and resilience.

Effect of Plant Growth-Promoting Rhizobacteria Synthetic Consortium on Growth, Yield, and Metabolic Profile of Lettuce (Lactuca sativa L.) Grown Under Suboptimal Nutrient Regime

Effect of Plant Growth-Promoting Rhizobacteria Synthetic Consortium on Growth, Yield, and Metabolic Profile of Lettuce (Lactuca sativa L.) Grown Under Suboptimal Nutrient Regime

Mechanisms of Rhizosphere Microorganisms in Regulating Plant Root System Architecture in Acidic Soils

Red soil occupies an important position in China's agriculturally cultivated land resources. However, its low pH value, high aluminum concentration, and inefficient phosphorus utilization limit the productivity of acidic red soil farmland. Plant roots exhibit remarkable plasticity, capable of absorbing water and nutrients and modulating root system architecture in response to biotic and abiotic stresses, either autonomously or through rhizosphere microorganisms. This study primarily investigates the regulatory effects of rhizosphere microorganisms, including plant growth-promoting rhizobacteria, such as arbuscular mycorrhizal fungi and rhizobia, and synthetic microbial consortia, on plant root system architecture. These regulatory mechanisms encompass the production of hormones, the release of volatile organic compounds, nitrogen fixation, phosphorus solubilization, and the improvement of rhizospheric soil structure. Such mechanisms can influence root biomass, branching, lateral roots, and root hair growth. Furthermore, we summarize new visualization methods for plant root system architecture and rhizosphere microorganisms, providing technical support for studying the regulation of root system architecture by rhizosphere microbes. Under acidic soil conditions, rhizosphere microorganisms serve as a crucial regulatory strategy. By adjusting plant root system architecture, they can enhance the productivity of acidic soils, representing a potential solution for ameliorating the constraints of acidic soils.

Applying microbial biostimulants and drought-tolerant genotypes to enhance barley growth and yield under drought stress.

With climate change, the frequency of regions experiencing water scarcity is increasing annually, posing a significant challenge to crop yield. Barley, a staple crop consumed and cultivated globally, is particularly susceptible to the detrimental effects of drought stress, leading to reduced yield production. Water scarcity adversely affects multiple aspects of barley growth, including seed germination, biomass production, shoot and root characteristics, water and osmotic status, photosynthesis, and induces oxidative stress, resulting in considerable losses in grain yield and its components. In this context, the present review aims to underscore the importance of selecting drought-tolerant barley genotypes and utilizing bio-inoculants constructed from beneficial microorganisms as an agroecological approach to enhance barley growth and production resilience under varying environmental conditions. Selecting barley genotypes with robust physiological and agronomic tolerance can mitigate losses under diverse environmental conditions. Plant Growth Promoting Rhizobacteria (PGPR) play a crucial role in promoting plant growth through nutrient solubilization, nitrogen fixation, phytohormone production, exopolysaccharide secretion, enzyme activity enhancement, and many other mechanisms. Applying drought-tolerant genotypes with bio-inoculants containing PGPR, improves barley's drought tolerance thereby minimizing losses caused by water scarcity.

Improving soil properties and Sesbania growth through combined organic amendment strategies in a coastal saline-alkali soil.

Improving the quality of degraded coastal saline-alkali soil and promoting plant growth are key challenges in the restoration of ecological functions in coastal regions. Organic ameliorants such as effective microbial (EM) agent, biochar, and organic compost have been proposed as sustainable solutions, but limited research has explored the combined effects of these amendments. This study investigates five organic improvement strategies: individual applications of EM, corn straw biochar (CSB), and sewage sludge-reed straw compost (COM), along with combined treatments of CSB+EM and COM+EM, on Sesbania growth in a pot experiment. The results demonstrated that, compared to the separate applications, the combined strategies (CSB+EM and COM+EM) exhibited a greater improvement in Sesbania growth; for instance, the plant dry weight was 4.61-12.1 times that of the control. The improved plant growth was linked to enhanced nutrient uptake and changes in soil properties. The combined strategies, particularly COM+EM, resulted in greater decreases in soil pH (decreased by 2.79%-3.49% compared to the control) and better improvements in soil nutrient content, quantity and quality of dissolved organic matter, microbial community diversity, and the abundance of plant growth-promoting rhizobacteria (PGPR), e.g., Bacillus. Spearman correlation and structural equation modeling confirmed that these soil improvements directly contributed to enhanced plant nutrient uptake. Overall, these findings suggest that combined strategies of COM+EM and CSB+EM, particularly the former, are highly effective for the remediation of coastal saline-alkali soils, offering a promising approach for improving soil fertility and plant productivity in degraded coastal ecosystems.

Enterobacter-inoculation altered the C, N contents and regulated biomass allocation in Reaumuria soongorica to promote plant growth and improve salt stress tolerance.

Soil salinization poses a significant ecological and environmental challenge both in China and across the globe. Plant growth-promoting rhizobacteria (PGPR) enhance plants' resilience against biotic and abiotic stresses, thereby playing a vital role in soil improvement and vegetation restoration efforts. PGPR assist plants in thriving under salt stress by modifying plant physiology, enhancing nutrient absorption, and synthesizing plant hormones. However, the mechanisms through which PGPR regulate the contents of carbon (C) and nitrogen (N), and biomass allocation of desert plant in response to salt stress is still unclear. This study explores the impact of PGPR on biomass allocation, C, and N contents of R. soongorica seedlings through a pot experiment. Strains P6, N20, and N21, identified as Enterobacter, were isolated from the rhizosphere of R. soongorica, and they exhibited various beneficial traits such as indole-3-acetic acid (IAA) production, phosphate solubilization, nitrogen fixation, and tolerance to up to 8% NaCl stress. We found that under NaCl stress, R. soongorica seedlings exhibit significant reductions in plant height, basal diameter, and root surface area (P<0.05). However, inoculation with strains P6, N20, and N21 reverses these trends. Compared to NaCl treatment alone, co-treatment with these strains significantly increases the biomass of roots, stems, and leaves, particularly root biomass, which increases by 99.88%, 85.55%, and 141.76%, respectively (P<0.05). Moreover, N contents decrease significantly in the roots, stems and leaves, C contents increase significantly in the roots and leaves compared to NaCl treatment (P<0.05). Specifically, N contents in roots decrease by 14.50%, 12.47%, and 8.60%, while C contents in leaves increase by 4.96%, 4.45%, and 4.94%, respectively (P<0.05). Additionally, stem and leaf biomasses exhibit a significant positive correlation with C contents and a significant negative correlation with N contents in these tissues. In conclusion, inoculation of Enterobacter strains enhanced the biomass of R. soongorica seedlings, regulated the biomass distribution, and modifies C and N contents to promote plant growth and improve salt stress tolerance. This study provides a novel adaptive strategy for the integrated use of PGPR and halophytes in saline-alkali soil improvement and vegetation restoration efforts.

Whole-genome sequencing and secondary metabolite exploration of the novel Bacillus velezensis BN with broad-spectrum antagonistic activity against fungal plant pathogens.

The utilization of chemical pesticides recovers 30%-40% of food losses. However, their application has also triggered a series of problems, including food safety, environmental pollution, pesticide resistance, and incidents of poisoning. Consequently, green pesticides are increasingly seen as viable alternatives to their chemical counterparts. Among these, Plant Growth-Promoting Rhizobacteria (PGPR), which are found within plant rhizosphere, stand out for their capacity to stimulate plant growth. Recently, we isolated a strain, BN, with broad-spectrum antimicrobial activity from the rhizosphere of Lilium brownii. Identification revealed that this strain belongs to the species Bacillus velezensis and exhibits significant inhibitory effects against various fungal plant pathogens. The complete genome sequence of B. velezensis BN consists of a circular chromosome with a length of 3,929,791 bp, includes 3,747 protein-coding genes, 81 small RNAs, 27 rRNAs, and 86 tRNAs. Genomic analysis revealed that 29% of the genes are directly involved in plant growth, while 70% of the genes are indirectly involved. In addition, 12 putative biosynthetic gene clusters were identified, responsible for the synthesis of secondary metabolites, such as non-ribosomal peptides, lanthipeptides, polyketides, siderophores, and terpenes. These findings provide a scientific basis for the development of efficient antimicrobial agents and the construction of biopesticide production platforms in chassis cells.

Evaluating the potential of Acinetobacter calcoaceticus in alleviation of aluminium stress in Triticum aestivum.

Soil contamination with toxic heavy metals [such as aluminum (Al)] is becoming a serious global problem due to the rapid development of the social economy. Although plant growth-promoting rhizo-bacteria (PGPR) are the major protectants to alleviate metal toxicity, the study of these bacteria to ameliorate the toxic effects of Al is limited. Therefore, the present study was conducted to investigate the combined effects of different levels of Acinetobacter calcoaceticus (5ppm and 10ppm) of accession number of MT123456 on plant growth and biomass, photosynthetic pigments, gas exchange attributes, oxidative stress and response of antioxidant compounds (enzymatic and nonenzymatic), and their specific gene expression, sugars, nutritional status of the plant, organic acid exudation pattern and Al accumulation from the different parts of the plants, which was spiked with different levels of Al [0µM (i.e., no Al), 50µM, and 100µM] using aluminum sulfate [Al2(SO4)3] in wheat (Triticum aestivum L.). Results from the present study revealed that the Al toxicity induced a substantial decreased in shoot length, root length, number of leaves, leaf area, shoot fresh weight, root fresh weight, shoot dry weight, root dry weight, chlorophyll-a, chlorophyll-b, total chlorophyll, carotenoid content, net photosynthesis, stomatal conductance, transpiration rate, soluble sugar, reducing sugar, non-reducing sugar contents, calcium (Ca2+), magnesium (Mg2+), iron (Fe2+), and phosphorus (P) contents in the roots and shoots of the plants. In contrast, increasing levels of Al in the soil signifcantly (P < 0.05) increased Al concentration in the roots and shoots of the plants, phenolic content, malondialdehyde (MDA), hydrogen peroxide (H2O2), electrolyte leakage (EL), fumaric acid, acetic acid, citric acid, formic acid, malic acid, oxalic acid contents in the roots of the plants. Although, the activities of enzymatic antioxidants such as superoxidase dismutase, peroxidase, catalase, ascorbate peroxidase and their specific gene expression in the roots and shoots of the plants and non-enzymatic such as phenolic, favonoid, ascorbic acid, and anthocyanin contents were initially increased with the exposure of 50µM Al, but decreased by the increasing the Al concentration 100µM in the soil. Addition of A. calcoaceticus into the soil signifcantly alleviated Al toxicity effects on T. aestivum by improving photosynthetic capacity and ultimately plant growth. Increased activities of antioxidant enzymes in A. calcoaceticus-treated plants seem to play a role in capturing stress-induced reactive oxygen species as was evident from lower levels of MDA, H2O2, MDA, and EL in A. calcoaceticus-treated plants. Research findings, therefore, suggested that A. calcoaceticus application can ameliorate Al toxicity in T. aestivum seedlings and resulted in improved plant growth and composition under metal stress as depicted by balanced exudation of organic acids.