Growth-promoting Rhizobacteria Research Articles

Leaf proteomics of sugarcane inoculated with growth-promoting rhizobacterium and fertilized with molybdenum

Leaf proteomics of sugarcane inoculated with growth-promoting rhizobacterium and fertilized with molybdenum

Synergistic interplay between ABA-generating bacteria and biochar in the reduction of heavy metal accumulation in radish, pakchoi, and tomato

Heavy metal (HM) contamination is an environmental concern that threatens the agricultural product safety and human health. To address this concern, we developed a novel strategy involving the synergistic application of Azospirillum brasilense, a growth-promoting rhizobacterium which produces abscisic acid (ABA), and biochar to minimize HM accumulation in the edible parts of vegetable crops. Compared to A. brasilense or biochar alone, the concentrations of Cd, Ni, Pb, and Zn in radish (Raphanus sativus L.), pakchoi (Brassica chinensis L.), and tomato (Lycopersicon esculentum L.) decreased by 18–63% and 14–56%, respectively. Additionally, the synergistic treatment led to a 14–63% decrease in the bioconcentration factor. The biomass of the edible parts of the three crops increased by 65–278% after synergistic treatment, surpassing the effects of single treatments. Furthermore, the synergistic application enhanced the SPAD values by 1–45% compared to single treatments. The MDA concentrations in stressed plants decreased by 16–39% with the bacteria-biochar co-treatment compared to single treatments. Co-treatment also resulted in increased soluble protein and sugar concentrations by 8–174%, and improvements in flavonoids, total phenols, ascorbic acid, and DPPH levels by 2–50%. Pearson correlation analysis and structural equation modeling revealed that the synergistic effect was attributed to the enhanced growth of A. brasilense facilitated by biochar and the improved availability of HMs in soils. Notably, although ABA concentrations were not as high as those achieved with A. brasilense alone, they were maintained at relatively high levels. Overall, the synergistic application of A. brasilense-biochar might have remarkable potential for reducing the accumulation of HMs while promoting growth and improving nutritional and antioxidant qualities in tuberous, leafy, and fruit crops.

Metabolic signatures of rhizobacteria‐induced plant growth promotion

Various root-colonizing bacterial species can promote plant growth and trigger systemic resistance against aboveground leaf pathogens and herbivore insects. To date, the underlying metabolic signatures of these rhizobacteria-induced plant phenotypes are poorly understood. To identify core metabolic pathways that are targeted by growth-promoting rhizobacteria, we used combinations of three plant species and three rhizobacterial species and interrogated plant shoot chemistry by untargeted metabolomics. A substantial part (50%-64%) of the metabolites detected in plant shoot tissue was differentially affected by the rhizobacteria. Among others, the phenylpropanoid pathway was targeted by the rhizobacteria in each of the three plant species. Differential regulation of the various branches of the phenylpropanoid pathways showed an association with either plant growth promotion or growth reduction. Overall, suppression of flavonoid biosynthesis was associated with growth promotion, while growth reduction showed elevated levels of flavonoids. Subsequent assays with 12 Arabidopsis flavonoid biosynthetic mutants revealed that the proanthocyanidin branch plays an essential role in rhizobacteria-mediated growth promotion. Our study also showed that a number of pharmaceutically and nutritionally relevant metabolites in the plant shoot were significantly increased by rhizobacterial treatment, providing new avenues to use rhizobacteria to tilt plant metabolism towards the biosynthesis of valuable natural plant products.

Application of Biofertilizers in crop production: A review

Nutritious foods are needed for the continuously growing population together with the nutrient for plant growth and production. Inorganic chemical-based fertilizers have been base and are used heavily in today’s soil management procedures, posing serious health and environmental concern. Biofertilizer has been recognized as a reasonable solution for improving soil fertility and crop output in sustainable farming. The use of beneficial microorganisms as biofertilizers has escalated its importance in the agricultural industry due to its potential significance in food safety and sustainable crop production. Biofertilizers can be a valuable component of a comprehensive nutrient management strategy. Overall, nitrogen fixers (N-fixers), potassium and phosphorus solubilizers, growth-promoting rhizobacteria (PGPR), endo and ectomycorrhizal fungi, cyanobacteria, and other beneficial microscopic organisms are incorporated into biofertilizers. Utilizing bio-fertilizers, enhance nutrient and water uptake, plant development, and plant tolerance to abiotic and biotic impacts. These prospective biological fertilizers would play a essential role in soil production and sustainability and also in environmental protection, being eco-friendly and cost-effective inputs for farmers.

Insights into the Interactions among Roots, Rhizosphere, and Rhizobacteria for Improving Plant Growth and Tolerance to Abiotic Stresses: A Review.

Abiotic stresses, such as drought, salinity, heavy metals, variations in temperature, and ultraviolet (UV) radiation, are antagonistic to plant growth and development, resulting in an overall decrease in plant yield. These stresses have direct effects on the rhizosphere, thus severely affect the root growth, and thereby affecting the overall plant growth, health, and productivity. However, the growth-promoting rhizobacteria that colonize the rhizosphere/endorhizosphere protect the roots from the adverse effects of abiotic stress and facilitate plant growth by various direct and indirect mechanisms. In the rhizosphere, plants are constantly interacting with thousands of these microorganisms, yet it is not very clear when and how these complex root, rhizosphere, and rhizobacteria interactions occur under abiotic stresses. Therefore, the present review attempts to focus on root–rhizosphere and rhizobacterial interactions under stresses, how roots respond to these interactions, and the role of rhizobacteria under these stresses. Further, the review focuses on the underlying mechanisms employed by rhizobacteria for improving root architecture and plant tolerance to abiotic stresses.

Genomic Insights Into the Antifungal Activity and Plant Growth-Promoting Ability in Bacillus velezensis CMRP 4490.

The main objective of this study was to evaluate Bacillus velezensis strain CMRP 4490 regarding its ability to inhibit soil-borne plant pathogens and to increase plant growth. The study included evaluation of in vitro antifungal control, sequencing the bacterial genome, mining genes responsible for the synthesis of secondary metabolites, root colonization ability, and greenhouse studies for the assessment of plant growth–promoting ability. The strain was obtained from soil samples in the north of Paraná in Brazil and was classified as a B. velezensis, which is considered a promising biological control agent. In vitro assay showed that B. velezensis CMRP 4490 presented antagonistic activity against Sclerotinia sclerotiorum, Macrophomina phaseolina, Botrytis cinerea, and Rhizoctonia solani with a mycelial growth inhibition of approximately 60%, without any significant difference among them. To well understand this strain and to validate its effect on growth-promoting rhizobacteria, it was decided to explore its genetic content through genome sequencing, in vitro, and greenhouse studies. The genome of CMRP 4490 was estimated at 3,996,396 bp with a GC content of 46.4% and presents 4,042 coding DNA sequences. Biosynthetic gene clusters related to the synthesis of molecules with antifungal activity were found in the genome. Genes linked to the regulation/formation of biofilms, motility, and important properties for rhizospheric colonization were also found in the genome. Application of CMRP 4490 as a coating film on soybean increased from 55.5 to 64% on germination rates when compared to the control; no differences were observed among treatments for the maize germination. The results indicated that B. velezensis CMRP 4490 could be a potential biocontrol agent with plant growth–promoting ability.

EFECTO DE LA RIZOBACTERIA PROMOTORA DEL CRECIMIENTO VEGETAL Azospirillum brasilense SP245 EN LA FOSFOLIPASA D EN PLÁNTULAS DE TRIGO

Azospirillum brasilense es una rizobacteria promotora del crecimiento vegetal muy utilizada en agricultura. Los cambios moleculares estimulados en la planta por esta rizobacteria durante la interacción se conocen de manera parcial. Uno de los sitios primarios de contacto de la rizobacteria con la célula vegetal es la membrana plasmática. El objetivo de este estudio fue analizar el efecto de A. brasilense en la actividad de la fosfolipasa D (PLD) en raíces de plántulas de trigo (Triticum aestivum L.). La actividad de la enzima se determinó mediante la producción de ácido fosfatídico (AF), el cual es el producto de su catálisis. Plántulas inoculadas con una concentración de 106 unidades formadoras de colonias por mililitro (UFC mL-1) de la rizobacteria mostraron una reducción en la producción de AF, en un periodo de inoculación de 5 a 15 min. Esta reducción reflejó un descenso en la actividad de la PLD. La disminución se mantuvo 12 a 48 h, tiempo de duración del estudio y coincidió con la disminución en el crecimiento de las plántulas. La adición exógena de AF estimuló el crecimiento de las plántulas. La producción de AF también disminuyó cuando se adicionó ácido indol-3-acético a las plántulas, lo que permitió sugerir un papel en la modulación de la actividad de la PLD. Los resultados mostraron que la inoculación de plántulas de trigo con A. brasilense Sp245 disminuye la actividad de la PLD.

The Response of Maize to Inoculation with Arthrobacter sp. and Bacillus sp. in Phosphorus-Deficient, Salinity-Affected Soil.

Salinity and phosphorus (P) deficiency are among the most serious soil factors constraining crop productivity. A proposed strategy for alleviating these stresses is supporting plants by inoculation with growth-promoting rhizobacteria (PGPR). Here, a comparison of the ability of two maize composite and two F1 hybrid varieties to tolerate a P deficiency in either a saline or a non-saline environment showed that the uptake of nutrients by all four entries was significantly reduced by the imposition of both soil salinity and P deficiency, and that their growth was compromised to a similar extent. Subsequently, the ameliorative effect of inoculation with three strains of either Arthrobacter sp. or Bacillus sp. in an environment, which suffered simultaneously from salinity and P deficiency, was investigated. Inoculation with each of the strains was found to limit the plants’ uptake of sodium cations, to increase their uptake of potassium cations, and to enhance their growth. The extent of the growth stimulation was more pronounced for the composite varieties than for the F1 hybrid ones, although the amount of biomass accumulated by the latter, whether the plants had been inoculated or not, was greater than that of the former varieties. When the bacterial strains were cultured in vitro, each of them was shown as able to produce the phytohormones auxin, abscisic acid, gibberellins, and cytokinins. The implication is that since the presence in the rhizospere of both Arthrobacter sp. and Bacillus sp. strains can support the growth of maize in salinity-affected and P deficient soils in a genotype-dependent fashion, it is important to not only optimize the PGPR strain used for inoculation, but also to select maize varieties which can benefit most strongly from an association with these bacteria.

Root growth in tomato seedlings in response to bacterial inoculation Serratia sp.

Growth-promoting rhizobacteria are soil bacteria that inhabit the surrounding root, and are directly or indirectly involved in promoting plant growth and development. The productivity efficiency of these groups of microorganisms can be applied to planting crops, providing an interesting alternative for minimize the negative effects of water deficit. The objective of this study was to verify if the mechanism of growth promotion of the bacterium is similar to that promoted by polyethylene glycol (PEG) and to compare the possible effects of water stress on the tomato against the effects of inoculation of the bacterium Serratia sp. The methodology was based on in vitro bioassays using tomato (Solanum lycopersicum L.) seedlings, kept in a growth chamber with temperature of 25 °C and photoperiod of 12 hours. The results revealed that the promotion of tomato root growth by Serratia sp. is similar to that promoted by PEG 7%, differing significantly from the results found with different doses of indoleacetic acid (IAA). The promotion of root growth in tomatoes by Serratia sp. and PEG 7% partly indicates a physical effect, since the water restriction imposed by the PEG molecule decreases the water movement capacity, also observed by bacteria, when colonizing plant tissues and cells (biofilm) reducing the hydraulic conductivity of water through the root. Stimulation to promote root growth in tomatoes cannot be reproduced by auxin.

Draft Genome Sequence of a Potential Plant Growth-Promoting Rhizobacterium, Pseudomonas sp. Strain CK-NBRI-02

Pseudomonas sp. strain CK-NBRI-02 is a potential plant growth-promoting Gram-negative rhizobacterium isolated from the rhizosphere of maize plants growing in fields in Srinagar, Jammu, and Kashmir, India. Here, we report a 5.25-Mb draft assembly of the genome sequence of Pseudomonas sp. strain CK-NBRI-02 with an average G+C content of 62.47%.

Root inoculation of green bell pepper (Capsicum annum) with Bacillus amyloliquefaciens BBC047: effect on biochemical composition and antioxidant capacity.

Consumption of bell peppers is recommended because of their bioactive compound content and their positive effects on health. Growth-promoting rhizobacteria are popular because of their ability to promote plant growth by improving the fixation of nutrients or by inducing a systemic response. Green bell pepper (Capsicum annum) roots were inoculated with an autochthonous strain of Bacillus amyloliquefaciens, at different stages of development: T1, inoculation in the seedbed before transplant; T2, inoculation at and after transplant; T3, inoculation in the seedbed, at and after transplant. Bell pepper plants without inoculation were considered as control. Physicochemical composition and antioxidant activity of the fruits were measured to select the best treatment. T1 increased crude proteins, fat, Ca, Fe, vitamin C, total phenolic content, antioxidant capacity by DPPH and by ORAC. On the other hand, T1 decreased reducing sugars, K and Cu content. No significant differences for total carbohydrates, ash and photosynthetic pigments were found. Inoculated green bell peppers have enhanced its functional value and could be considered as an important source of bioactive compounds with elevated antioxidant activity. © 2019 Society of Chemical Industry.

Enhancement of alfalfa yield and quality by plant growth-promoting rhizobacteria under saline-alkali conditions.

Bacteria with 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity could decrease the ethylene level, confer resistance of plant, and stimulate plant growth under biotic and abiotic stress conditions. Plant growth-promoting rhizobacteria (PGPR) strains Enterobacter aerogenes (LJL-5) and Pseudomonas aeruginosa (LJL-13) were obtained from the rhizosphere of alfalfa grown under saline-alkali conditions. The ACC deaminase activity of E. aerogenes (LJL-5) and Ps. aeruginosa (LJL-13) was approximately 2-5 µmol mg-1 h-1 . indole acetic acid synthesis was increased with the increasing concentration of l-tryptophan. Siderophore production and phosphate solubilization in Ps. aeruginosa (LJL-13) were higher than those in E. aerogenes (LJL-5). Compared to the non-inoculated seedlings (1.31 ng mL-1 h-1 ), inoculated alfalfa seedlings with E. aerogenes (LJL-5) (0.90 ng mL-1 h-1 ) and Ps. aeruginosa (LJL-13) (0.78 ng mL-1 h-1 ) emitted lower levels of ethylene. Under saline-alkali conditions in the greenhouse, inoculation with E. aerogenes (LJL-5) and Ps. aeruginosa (LJL-13) increased the biomass, soil and plant analyzer development (SPAD), and P content of alfalfa plants, and also induced the activity of antioxidant enzymes (superoxide dismutase, peroxidase and catalase), promoted the accumulation of antioxidant substances and removed various harmful substances. Under saline-alkali conditions in the field (2012, 2013, and 2014), inoculation of alfalfa with E. aerogenes (LJL-5) and Ps. aeruginosa (LJL-13) significantly increased the shoot height, fresh and dry weights, yield and crude protein content of alfalfa plants, but decreased the fiber content. Two PGPR strains were isolated from the rhizosphere of alfalfa in saline-alkali conditions. Both strains could promote alfalfa growth in saline-alkali soil, and could be used as biofertilizer to promote plant growth under stress and reduce environmental pollution caused by fertilizers simultaneously. © 2018 Society of Chemical Industry.

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Effects of rhizobacteria on the respiration and growth of Cerasus sachalinensis Kom. seedlings

In this study, we investigated the influence of rhizosphere microorganisms on seed germination and root metabolism in Cerasus sachalinensis Kom. We inoculated C. sachalinensis plants with suspensions of dominant bacterial strains isolated from their rhizosphere. Four bacterial strains each with significant growth-promoting or growth-inhibiting effects were screened from the efficient root-colonizing microorganisms. The number of actinomycetes increased and that of fungi decreased significantly in the seedling rhizospheres after rhizobacteria treatment. The growth-promoting bacteria slightly affected the respiration rates and respiratory pathway enzymes, but significantly improved root viability, root carbohydrate concentration and seedling growth. Bacillus cereus, Staphylococcus sp. and Pseudomonas fluorescens were identified as the growth-promoting rhizobacteria; one strain could not be identified. After inoculation with the growth-inhibiting bacteria, the number of fungal colonies in the seedling rhizospheres increased and root viability and respiration rate as well as starch and sucrose accumulation in the roots significantly decreased. The glycolysis, pentose phosphate and alternative oxidase pathways became the major pathways of respiratory metabolism after inoculation with the growth-inhibiting bacteria. The height, leaf number, growth and dry weight of the seedlings decreased significantly in plants inoculated with the growth-inhibiting bacteria. Inoculation of C. sachalinensis rhizosphere with growth-promoting and growth-inhibiting bacteria affected the soil environmental factors such as microbial group composition, nutrient concentration and seedling biomass.

Bacteria as growth-promoting agents for citrus rootstocks

The microbial community plays an essential role in maintaining the ecological balance of soils. Interactions between microorganisms and plants have a major influence on the nutrition and health of the latter, and growth-promoting rhizobacteria can be used to improve plant development through a wide range of mechanisms. Therefore, the objective of the present study was to evaluate bacteria as growth-promoting agents for citrus rootstocks. A total of 30 bacterial isolates (11 of Bacillus spp., 11 actinobacteria, and 8 lactic acid bacteria) were evaluated in vitro for indoleacetic acid production, phosphate solubilization, and nitrogen (N) fixation. In vivo testing consisted of growth promotion trials of the bacterial isolates that yielded the best results on in vitro tests with three rootstocks: Swingle citrumelo [Citrus×paradisi Macfad cv. Duncan×Poncirus trifoliata (L.) Raf.], Sunki mandarin (Citrus sunki Hort. ex Tan), and rangpur (Citrus×limonia Osbeck). The parameters of interest were height, number of leaves, stem diameter, shoot and root dry mass, and total dry mass at 150days after germination. The results showed that most bacterial isolates were capable of IAA production. Only one lactic acid bacterium isolate (BL06) solubilized phosphate, with a high solubilization index (PSI>3). In the actinobacteria group, isolates ACT01 (PSI=2.09) and ACT07 (PSI=2.01) exhibited moderate phosphate-solubilizing properties. Of the Bacillus spp. isolates, only CPMO6 and BM17 solubilized phosphate. The bacterial isolates that most fixated nitrogen were BM17, ACT11, and BL24. In the present study, some bacteria were able to promote growth of citrus rootstocks; however, this response was dependent on plant genotype and isolate. Bacillus spp. BM16 and CPMO4 were able to promote growth of Swingle citrumelo. In Sunki mandarin plants, the best treatment results were obtained with BM17 (Bacillus sp.) and ACT11 (actinobacteria). For Rangpur lime rootstock, only BM05 (Bacillus sp.) was able to promote increase in two parameters assessed, height and number of leaves. When the bacterial isolates were used in mixture there was not promoted growth of plants on rootstocks. This fact may be associated with the different mechanisms of action of each bacteria involved or with the presence of competition among the microorganisms of the mixture.

Physiological performance of rice seeds treated with thiamethoxam or rhizobacteria under different temperatures

This study aimed to evaluate, at 15, 20 and 25 ºC, the physiological potential and enzyme activity of seedlings from six samples of rice seeds stored for one year and treated with growth-promoting rhizobacteria (Pseudomonas synxantha) and the bioactivator thiametoxam. The following were evaluated: seed germination, first germination count, root protrusion speed index, emergence percentage and emergence speed index, shoot and root length and enzyme activity (esterases, α-amylase and peroxidases) at 15, 20 and 25 ºC. In these conditions, thiametoxam and the rhizobacteria P. synxantha (DFs 185) improved the physiological performance of rice seeds with physiological qualities at low temperatures (20 and 15 ºC) and did not change the expression of the esterase and peroxidase isoenzymes. The rhizobacteria P. synxantha (DFs 185) increased the expression of the enzyme α-amylase at low temperatures.

Indole acetic acid and phytase activity produced by rhizosphere bacilli as affected by pH and metals

The abilities to produce indole acetic acid (IAA) and mineralize organic phospho- rus by phytase are desirable traits in plant−growth promotion rhizobacteria (PGPR) particularly in Chilean Andisols which are characterized by low pH and high total P. However, little is known about the influence of soil properties that are specific to An- disol (low pH and metal toxicity) on the effectiveness of PGPR. Here, we assessed the effect of pH and metal cations on IAA and phytase activity of cell-associated proteins produced by two bacilli strains isolated from the rhizosphere of pasture plants. The production in vivo of IAA by Paenibacillus sp. SPT−03 was significantly increased (7−fold) when incubated in tenfold diluted culture medium, compared to the full-strength medium. At low pH (pH<5), phytase activity of cell−associated proteins and IAA production of Bacillus sp. MQH−19 was decreased, whereas they were increased in Paenibacillus sp. SPT−03. Moreover, phytase activity in vitro of cell−associated proteins and IAA production in both bacilli strains were signifi- cantly inhibited by 30−100% and 44−70% by concentrations of 10 mM and 350 µM Fe 3+ and Al 3+ , respectively. At 350 µM Mn 2+ IAA production was inhibited by 30−100% in both strains but there was no effect on phytase activity. This study shows that certain properties of Andisol may differentially affect some mechanisms related with PGPR efficiency.

Influence of a plant growth-promoting pseudomonad and vesicular-arbuscular mycorrhizal fungus on alfalfa and birdsfoot trefoil growth and nodulation

In a growth chamber study we examined the influence of a plant growth-promoting rhizobacterium, Pseudomonas putida R-20, and an acid-tolerant vesicular-arbuscular mycorrhizal (VAM) fungus, Glomus intraradices 25, on Medicago sativa L. and Lotus corniculatus L. growth and nodule development. Seedlings were planted in an acidic (pH 5.5), P-deficient soil containing re-established native microflora (minus VAM) and appropriate rhizobia, and inoculated with the rhizobacterium, the VAM fungus, or both. The plants were assayed at three intervals for up to 10–11 weeks. The growth-promoting rhizobacteria alone increased alfalfa shoot mass by 23% compared to all other treatments, but only at 8 weeks of growth, apparently by promoting nodulation and N2 fixation (acetylene reduction activity). The presence of VAM, either alone or in combination with the rhizobacteria, generally decreased root length but only at 8 weeks also. As a group, the inoculation treatments increased all nodular measurements by 10 weeks of growth. Few treatment effects were found at 7 and 9 weeks for birdsfoot trefoil; neither plant nor nodular measurements differed among treatments. By 11 weeks, shoot mass was increased by the rhizobacteria alone by 36% compared to the control. As a group, the inoculation treatments all showed increased nodular responses by this time. The rhizobacteria stimulated mycorrhizal development on both plant species, but only at the initial samplings. No synergistic effects between the plant growth-promoting rhizobacterium and VAM inoculation were found. Although these results lend credence to the concept of managing microorganisms in the rhizosphere to improve plant growth, they emphasize the necessity for a more thorough understanding of microbial interactions as plants mature.