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Salvinia auriculata Aublet is a floating aquatic plant, capable of absorbing the excess of nutrients and water contaminants and can be used in effluent treatment plants. The ability to survive in degraded areas may be related to the association with beneficial bacteria capable of promoting plant growth. However, little is known about the microbiota associated with this aquatic plant and its potential application to the aquatic environment. In this sense, this work aims to identify bacteria associated with S. auriculata that could be able to promote plant growth. Eighteen bacterial strains were identified by sequencing of the 16S rRNA gene, belonging to the genera Agrobacterium, Bacillus, Curtobacterium, Enterobacter, Pseudomonas, Siccibacter, and Stenotrophomonas. All isolates produced indole compounds, 12 fixed N2, and 16 solubilized phosphate. A new strain of Enterobacter (sp 3.1.3.0.X.18) was selected for inoculation into S. auriculata. For this purpose, 500 mL of nutrient solution and 1 g of the plant were used in the control and inoculated conditions. Enterobacter inoculation promoted a significant increase (p ≤ 0.05) in fresh plant biomass (17%) after 4 days of cultivation. In summary, the present study characterized 18 plant-growth-promoting bacteria isolated from S. auriculata with potential for biotechnological application, such as the production of bioinoculants or biomass resources, to protect or improve plant growth under conditions of stress. [ABSTRACT FROM AUTHOR]

Currently, the use of bio-inputs is increasing due to the need to reduce the use of agrochemicals. However, one of the limitations is to preserve the viability of the living microorganisms, so it is important to find an alternative that allows us to obtain different metabolites to produce it. We evaluated three different interactions (contact, diffusible and volatile compounds) in vitro in Arabidopsis thaliana (At) seedlings with the strain Cytobacillus firmus M10 and its filtered secondary metabolites (M10F). The results showed that the seedlings inoculated by contact with the filtrate (AtM10F) presented increases in root length (30 %) and leaf area (33 %), as well as in the volatile interaction (At/M10F) with respect to the uninoculated treatment. For both interactions, the seedlings inoculated with the bacteria by contact (AtM10) and volatile (At/M10) obtained greater biomass (48 and 57 %). Subsequently, an evaluation at the end of the A. thaliana cycle showed that the treatments obtained by contact and distance when reinoculated with the bacteria and the filtrate (AtM10, At-M10 and AtM10F) obtained 50 % more seed yield than the control treatment, while AtM10F presented 72 %, while At/M10F presented the highest no. of siliques and seeds, which increased the yield by 65 %. In the Solanum lycopersicum (Sl) experiment, the filtrate (SlM10F) showed significant differences in seedling height, leaf length and width (23, 24 and 36 %, respectively). It also promoted an increase in fresh and dry weight, producing a greater root area and larger leaves compared to the control (Sl) and the bacteria (SlM10). We performed a qualitative characterization of the secondary metabolites present in the filtrate, where we found 2,4-DTBP, sylvopinol, isophthaladehyde, and eicosane of interest with possible growth-promoting effects on A. thaliana and tomato. We identified volatile compounds present in plant-microorganism and plant-filtrate interactions as possible precursors in the induction of plant growth, among which phenols, alcohols, aldehydes, alkanes, and alkenes stand out. Most of the analyzed compounds have not been found in the literature with reports of growth promoters, is important to mention that due to their characteristic functional groups they can derive and trigger the synthesis of new molecules with agronomic application.

In this study, we analyzed the hypothesis that the combination of Nitrospirillum amazonense strain BR11145 with biological fertilizer prepared using Microgeo® and native microbiome from location of the product application results in morphological and nutritional gains for the initial development of sugarcane plants and soil chemistry. For this purpose, pre-sprouted sugarcane seedlings were grown in a greenhouse mesocosm experiment using soil amended with nitrogen/phosphorus/potassium fertilizer. The experimental treatments consisted of: 1) biological fertilizer with the addition of N. amazonense (100 mL ha-1), 2) biological fertilizer without the addition of N. amazonense, 3) inoculation with N. amazonense at a dose of 100 mL ha-1 with 2x108 viable cell mL-1, 4) inoculation with N. amazonense at a dose of 200 mL ha-1 with 2x108 viable cell mL-1, and 5) control, without the addition of biological fertilizer and N. amazonense. The biological fertilizer was applied at dose of 300 L ha-1, which was split at planting (200 L ha-1) and in the post-emergence phase (100 L ha-1). After 164 days of planting, it was detected an increase in leaf length +3, number of green leaves, leaf area and sulfur content in the leaves of sugarcane plants that received the biological fertilizer with the addition of N. amazonense. In conclusion, the combination of N. amazonense with biological fertilizer revealed positive effects through morphological and nutritional characteristics in sugarcane plants during their early stages of development when compared to plants grown only with the inoculation of N. amazonense, biological fertilizer or mineral fertilizers, with few notable positive effects on soil chemistry. [ABSTRACT FROM AUTHOR]

Salvinia auriculata Aublet is a floating aquatic plant, capable of absorbing the excess of nutrients and water contaminants and can be used in effluent treatment plants. The ability to survive in degraded areas may be related to the association with beneficial bacteria capable of promoting plant growth. However, little is known about the microbiota associated with this aquatic plant and its potential application to the aquatic environment. In this sense, this work aims to identify bacteria associated with S. auriculata that could be able to promote plant growth. Eighteen bacterial strains were identified by sequencing of the 16S rRNA gene, belonging to the genera Agrobacterium, Bacillus, Curtobacterium, Enterobacter, Pseudomonas, Siccibacter, and Stenotrophomonas. All isolates produced indole compounds, 12 fixed N2, and 16 solubilized phosphate. A new strain of Enterobacter (sp 3.1.3.0.X.18) was selected for inoculation into S. auriculata. For this purpose, 500 mL of nutrient solution and 1 g of the plant were used in the control and inoculated conditions. Enterobacter inoculation promoted a significant increase (p ≤ 0.05) in fresh plant biomass (17%) after 4 days of cultivation. In summary, the present study characterized 18 plant-growth-promoting bacteria isolated from S. auriculata with potential for biotechnological application, such as the production of bioinoculants or biomass resources, to protect or improve plant growth under conditions of stress.

Besides being a significant part of the Brazilian national economy, the common bean is a legume whose grains are part of the daily diet of the population of developing nations globally. Combining N-fixing bacteria and plant phytohormone producers through the use of inoculants is an alternative to improve plant growth and increase grain yield in the common bean production system. This study aimed to evaluate the effect of co-inoculation doses with Rhizobium tropici and Azospirillum brasilense, applied in the planting groove, on nodulation, growth and productivity parameters of the common bean. Five field experiments were conducted in a randomized block design with four replications. Restrictions were formulated, namely: absolute control, without fertilization and without co-inoculation (AC); nitrogen fertilization (NfT); single inoculation of R. tropici (Rt); R. tropici + one dose of A. brasiliense (Rt + Ab1f); R. tropici + two doses of A. brasiliense (Rt + Ab2f); R. tropici + three doses of A. brasiliense (Rt + Ab3f); R. tropici + four doses of A. brasiliense (Rt + Ab4f) and R. tropici + three doses of A. brasiliense (RP). The number of nodules (NN), nodule dry mass (NDM), aerial dry mass (ADM), root dry mass (RDM), pod number (NP), number of grains (NG), mass of 100 grain (100G) and grain yield (GY) were taken. The Rt + Ab4f co-inoculation provided a significant increase in NN, NDM, ADM and RDM values than the Rt and AC treatments. In addition, it also presented the highest GY stability, with an average production of 3499 kg ha− 1 from the five sites, which represents an increase of 15.4%, 14.8%, 11.0%, and 1.0% as compared to Rt, AC, RP, and NfT treatments, respectively. The results indicate the feasibility of the use of co-inoculation with R. tropici and A. brasilense in commercial production farms and for small producers in several countries of the world with similar edaphoclimatic conditions, reducing the use of nitrogen fertilizers, production costs and the prevention of negative environmental impacts. [ABSTRACT FROM AUTHOR]

ABSTRACT Inoculating corn with diazotrophic bacteria as growth promoters has been demonstrated to be an efficient agricultural practice in Brazil, mainly due to the root stimulation they provide to plants. This study investigates the corn (Zea mays L.) root architecture in a greenhouse assay where A. baldaniorum Sp245 and H. seropedicae ZAE94 strains were inoculated and evaluated for 22 days under two N levels: 0.6 and 6 mmol L-1 of N. Short-term bioassays were conducted to assess the plant’s response to the addition of indole-acetic acid, two bacterial populations, and two corn genotypes, utilizing image capture software WinRhizo Pro. The growth and distribution of tips, crossing, and length of fine roots were determined to be the most sensitive aspects to inoculation and indole-acetic acid induction. These responses were influenced by the genotype and the number of bacterial cells present. Biomass accumulation analyses quantified these modifications after a 22-day period. Additionally, the growth response was found to be more significant when applying the Hs-ZAE94 strain to plants fertilized with a higher dose of nitrogen (6.0 mmol L-1), and this response was positively correlated with bioassay data. Selected strains used as an inoculant can improve root architecture and, consequently, the N use efficiency.

The influence of the culture medium without bacterial cells, obtained after the cultivation of endophytic bacteria Priestia endophytica UCM B-5715, on the growth and synthesis of some metabolites in lettuce and chicory seedlings under in vitro conditions was studied. Bacteria were cultivated in liquid LB medium at 37 ºC for 24 h with periodic stirring. The culture fluid was separated from the cell biomass. For preparing the test solution, the supernatant was sterilized by filtration through a filter with a pore diameter of 0.2 µm (Sartorius, Minisart) and diluted with sterile distilled water. The 20% culture fluid (30 µl/plant) was applied to 3-day-old seedlings. In 28 days root and shoot weights of treated chicory plants were 54.3 ± 6.9 and 260.0 ± 20.2 mg, respectively (8.0 ± 0.7 and 91.4 ± 7.0 mg for the control plants). Total flavonoid content and antioxidant activity increased only in chicory plants after the addition of the test solution. Significant changes in the metabolism of treated plants were detected. In the treated lettuce plants asparagine content increased compared to the control (90 vs 22 µg/g, p < 0.1). The median content of fructose was also higher in treated lettuce and chicory plants (1469 vs 73 µg/g and 2278 vs 1051 µg/g). Therefore, the use of culture fluid obtained after the cultivation of P. endophytica UСM B-5715 stimulated the growth of lettuce and chicory plants, affecting the synthesis of some compounds in single-treated plants. These results indicate the potential of compounds excreted during bacterial growth to create natural growth stimulators. [ABSTRACT FROM AUTHOR]

The present study aimed to evaluate the effects of nitrogen fertilization and inoculation with Azospirillum brasilense on the quality of Cantaloupe melon fruit. Two experiments were carried out, one with direct sowing and the other with transplanted seedlings, in a 2 × 2 factorial scheme with five replications. For the constitution of the treatments were used: presence and absence of inoculation with A. brasilense and the presence and absence of nitrogen application. The fresh weight, longitudinal and transverse diameters, skin and pulp thickness, soluble solids content and titratable acidity of the fruits were evaluated. The application of nitrogen fertilizer and A. brasilense increased the biometric variables of the fruits when they were grown from the transplant of seedlings. However, when direct sowing was carried out, the effect of nitrogen sources was positively significant in terms of the organoleptic characteristics of melon fruits. The use of nitrogen fertilizer and A. brasilense for transplanted seedlings and A. brasilense for plants sown directly, is necessary to improve the development, productivity and quality of Cantaloupe melon fruit. [ABSTRACT FROM AUTHOR]

The problem of phosphorus and nitrogen deficiency in agricultural soils has been solved by adding chemical fertilizers. However, their excessive use and their accumulation have only contributed to environmental contamination. Given the high content of nutrients in biosolids collected from a food industry waste treatment plant, their use as fertilizers was investigated in Zea mays plants grown in sandy loam soil collected from a semi-desert area. These biosolids contained insoluble phosphorus sources; therefore, given the ability of Azotobacter nigricans to solubilize phosphates, this strain was incorporated into the study. In vitro, the suitable conditions for the growth of Z. mays plants were determined by using biosolids as a fertilizer and A. nigricans as a plant-growth-promoting microorganism; in vitro, the ability of A. nigricans to solubilize phosphates, fix nitrogen, and produce indole acetic acid, a phytohormone that promotes root formation, was also evaluated. At the greenhouse stage, the Z. mays plants fertilized with biosolids at concentrations of 15 and 20% (v/w) and inoculated with A. nigricans favored the development of bending strength plants, which was observed on the increased stem diameter (>13.5% compared with the negative control and >7.4% compared with the positive control), as well as a better absorption of phosphorus and nitrogen, the concentration of which increased up to 62.8% when compared with that in the control treatments. The interactions between plants and A. nigricans were observed via scanning electron microscopy. The application of biosolids and A. nigricans in Z. mays plants grown in greenhouses presented better development than when Z. mays plants were treated with a chemical fertilizer. The enhanced plant growth was attributed to the increase in root surface area. [ABSTRACT FROM AUTHOR]

The use of biological inputs is an interesting approach to optimize crop production and reduce the use of chemical inputs. Understanding the chemical communication between bacteria and plants is critical to optimizing this approach. Recently, we have shown that Sphingomonas (S.) sediminicola can improve both nitrogen supply and yield in pea. Here, we used biochemical methods and untargeted metabolomics to investigate the chemical dialog between S. sediminicola and pea. We also evaluated the metabolic capacities of S. sediminicola by metabolic profiling. Our results showed that peas release a wide range of hexoses, organic acids, and amino acids during their development, which can generally recruit and select fast-growing organisms. In the presence of S. sediminicola, a more specific pattern of these molecules took place, gradually adapting to the metabolic capabilities of the bacterium, especially for pentoses and flavonoids. In turn, S. sediminicola is able to produce several compounds involved in cell differentiation, biofilm formation, and quorum sensing to shape its environment, as well as several molecules that stimulate pea growth and plant defense mechanisms. [ABSTRACT FROM AUTHOR]

Background: The tolerance of plants against abiotic stresses can be greatly influenced by their interaction with microbes. In lowland rice (Oryza sativa) production, the iron toxicity of the soils constitutes a major constraint. Although there are tolerant cultivars, the mechanisms underlying the tolerance against excess iron are not fully understood. Even less is known about the role of microbes in the response to iron toxicity. Aim: In the study presented here, the effects of different Bacillus isolates on the accumulation and distribution of iron within the shoots of different rice cultivars grown under iron toxicity were analyzed. Methods: Three lowland rice cultivars with contrasting tolerance to iron toxicity (IR31785‐58‐1‐2‐3‐3, Sahel 108, Suakoko 8) were inoculated with three Bacillus isolates (two B. pumilus and one B. megaterium) and, after 1 week, exposed to excess iron (1,000 ppm) for 8 days. Tolerance was evaluated by leaf symptom scoring. Results: Bacterial inoculation mitigated leaf symptoms in the sensitive cultivar IR31785‐58‐1‐2‐3‐3 despite no significant differences in shoot iron concentration between inoculated and noninoculated plants. In the tolerant excluder cultivar, Suakoko 8, leaf symptoms were exacerbated when inoculated with B. pumilus Ni9MO12. While the total shoot Fe concentration was not affected in this bacteria × cultivar combination, the distribution of iron within the shoot was clearly disturbed. Tolerance to iron toxicity of the tolerant includer cultivar, Sahel 108, was not affected by Bacillus inoculation. Conclusion: In conclusion, our results show that Bacillus inoculation can affect the tolerance of lowland rice to iron toxicity and that the effects strongly depend on the bacteria × cultivar combination. [ABSTRACT FROM AUTHOR]

Ground-level ozone (O3) pollution often rise in the summer and coincide with drought stress, which alters the relationships between trees and associated microbial communities in a manner that can have pronounced effects on associated biological activity and ecosystem integrity. Discerning the responses of phyllosphere microbial communities to O3 and water deficit could highlight the ability of plant-microbe interactions to either exacerbate or mitigate the effects of these stressors. Accordingly, this study was designed as the first report to specifically interrogate the impacts of elevated O3 and water deficit stress on phyllospheric bacterial community composition and diversity in hybrid poplar saplings. Significant reductions in phyllospheric bacterial alpha diversity indices were observed, with clear evidence of significant time × water deficit stress interactions. The combination of elevated O3 and water deficit stress shifted in the bacterial community composition over sampling time, resulted in significant increases in the relative abundance of the dominant Gammaproteobacteria phyla together with reductions in Betaproteobacteria. An increased prevalence of Gammaproteobacteria may represent a potential diagnostic dysbiosis-related biosignature associated with poplar disease risk. Significant positive correlations were observed between both Betaproteobacteria abundance and diversity indices and key foliar photosynthetic traits and isoprene emissions, whereas these parameters were negatively correlated with Gammaproteobacteria abundance. These findings suggest that the photosynthesis-related properties in plant leaves are closely related to the makeup of the phyllosphere bacterial community. These data provide novel insight into how plant-associated microbes can help maintain plant health and the stability of the local ecosystem in O3-polluted and dried environments.

• Drought tolerant plant species had better phytoremediation potential in contaminated soil. • Plant-bacteria interaction enhanced bioremediation potential in TPHs contaminated soils. • Eucalyptus showed better bioremediation potential among experimental plants. • Application of fertilizer improved bioremediation efficiency of plant and bacteria. Ex-Situ bioremediation techniques such as synthetic surfactants and bioreactors to detoxify petroleum contaminated soil are costly and have harmful environmental consequences. This study was conducted to evaluate the intrinsic bioremediation potential of native, compatible and drought-tolerant plants and bacteria for removing total petroleum hydrocarbons (TPHs) from the soil. Furthermore, the potential of fertilizer for increasing the bioremediation capacity of these organisms was assessed. The study was performed as a completely randomized factorial design experiment with four replications. The plant treatments were Opuntia ficus-indica (P1), Eucalyptus camaldulensis, (P2) and Nerium oleander (P3). The bacteria treatments were Bacillus pumilus (B1), Pseudomonas putida (B2), and the combined use of these two bacteria and a fertilizer recommendation (B1B2F). The control treatment included only contaminated soil without plant, bacteria, and fertilizer. The results indicated that plant and bacteria treatments enhanced the decomposition of soil TPHs significantly (α=0.01). P2B1B2F was found to be the most efficient treatment, removing 77.30% of soil TPHs. Eucalyptus camaldulensis cultivation along with P. putida (P2B2) reduced TPHs by 69.60%. P. putida was more efficient than B. pumilus in reducing TPHs. Interactions between plants and bacteria increased root and total dry weight of plants significantly (α=0.01). Application of bacteria and the fertilizer recommendation increased the decomposition rate of TPHs and improved phytoremediation efficiency. Rehabilitation by Eucalyptus camaldulensis with bio-fertilization of soil using P. putida and chemical fertilizers is recommended for the bioremediation of soil contaminated with TPHs. [ABSTRACT FROM AUTHOR]

Biological remediation is an environmentally compatible technology, which can lead to the removal of contaminants from soil. The present paper aims to investigate the bioremediation potential of six environmentally compatible plant species and two bacterial species. Furthermore, it studies the use of nutrition recommendation to accelerate plants and bacteria capacity for soil petroleum contaminants decomposition. The pot experiment is conducted as a factorial experiment in a completely randomized design with four replications. Plant cultivation and bacterial protocol inoculation treatments are the two factors applied. Plant treatments include three drought-tolerant tree and shrub plants (Eucalyptus camaldulensis, Nerium oleander, and Opuntia ficus indica) and three native rangeland plants (Medicago sativa, Agropyron trichophorum, and Atriplex canescens). Bacteria treatments include Bacillus pumilus and Pseudomonas putida and the combined use of these two bacteria with fertilizer recommendation protocol in accordance with the soil test. The control treatment is also considered. The gravimetric method is applied using an ultrasonic bath to determine total petroleum hydrocarbons in soil. The removal efficiency of total petroleum hydrocarbons in soil ranges between 50 and 78% in all treatments. Eucalyptus camaldulensis along with two bacteria and fertilizer protocol has maximum efficiency, removing 77.32% of total petroleum hydrocarbons. Medicago sativa decomposes 55.16 percent of total petroleum hydrocarbons without the need of fertilizer or microbes, outperforming other plants. In most plants, Pseudomonas putida is more successful than Bacillus pumilus. Furthermore, Pseudomonas putida along with fertilizer recommendation decomposes 67.02% of total petroleum hydrocarbons in soil. It is found that fertilizer protocol improves the phytoremediation efficiency. [ABSTRACT FROM AUTHOR]

Strawberry (Fragaria x ananassa, Duch.) is an important crop worldwide. However, since it is a highly demanding crop in terms of the chemical conditions of the substrate, a large part of strawberry production implies the application of large amounts of fertilizers in the production fields. This practice can cause environmental problems, in addition to increases in the fruit's production costs. In this context, applying plant growth-promoting bacteria in production fields can be an essential strategy, especially thanks to their ability to stimulate plant growth via different mechanisms. Therefore, this study aimed to test in vitro and in vivo the potential of bacteria isolated from strawberry leaves and roots to directly promote plant growth. The isolates were tested in vitro for their ability to produce auxins, solubilize phosphate and fix nitrogen. Isolates selected in vitro were tested on strawberry plants to promote plant growth and increase the accumulation of nitrogen and phosphorus in the leaves. The tested isolates showed an effect on plant growth according to biometric parameters. Among the tested isolates, more expressive results for the studied variables were observed with the inoculation of the isolate MET12M2, belonging to the species Brevibacillus fluminis. In general, bacterial inoculation induced strain-dependent effects on strawberry growth. In vitro and in vivo assays showed the potential use of the B. fluminis MET12M2 isolate as a growth promoter for strawberries. [ABSTRACT FROM AUTHOR]

Duckweeds (Lemnaceae) are representative producers in fresh aquatic ecosystems and also yield sustainable biomass for animal feeds, human foods, and biofuels, and contribute toward effective wastewater treatment; thus, enhancing duckweed productivity is a critical challenge. Plant-growth-promoting bacteria (PGPB) can improve the productivity of terrestrial plants; however, duckweed–PGPB interactions remain unclear and no previous study has investigated the molecular mechanisms underlying duckweed–PGPB interaction. Herein, a PGPB, Ensifer sp. strain SP4, was newly isolated from giant duckweed (Spirodela polyrhiza), and the interactions between S. polyrhiza and SP4 were investigated through physiological, biochemical, and metabolomic analyses. In S. polyrhiza and SP4 coculture, SP4 increased the nitrogen (N), chlorophyll, and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) contents and the photosynthesis rate of S. polyrhiza by 2.5-, 2.5-, 2.7-, and 2.4-fold, respectively. Elevated photosynthesis increased the relative growth rate and biomass productivity of S. polyrhiza by 1.5- and 2.7-fold, respectively. Strain SP4 significantly altered the metabolomic profile of S. polyrhiza, especially its amino acid profile. N stable isotope analysis revealed that organic N compounds were transferred from SP4 to S. polyrhiza. These N compounds, particularly glutamic acid, possibly triggered the increase in photosynthetic and growth activities. Accordingly, we propose a new model for the molecular mechanism underlying S. polyrhiza growth promotion by its associated bacteria Ensifer sp. SP4, which occurs through enhanced N compound metabolism and photosynthesis. Our findings show that Ensifer sp. SP4 is a promising PGPB for increasing biomass yield, wastewater purification activity, and CO2 capture of S. polyrhiza.[Graphic: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Introduction. Plant growth-promoting rhizobacteria have been successfully inserted in agriculture, aiming to find a better balance between agricultural production and environmental protection. However, there is a restriction on its application concerning the exploited species since the focus is on large-scale grain production, practically excluding small and medium-sized farms. Literature. Studies on the application of Azospirillum bacteria in horticultural species are still scarce, compared with those aimed at grain production. However, it appears that these bacteria are beneficial to the development and production of vegetables, whether they produce leaves, stems, bulbs, flowers, fruits, roots, or tubers, and may result in monetary gains, especially for small and medium agricultural producers. Conclusions. The use of Azospirillum bacteria to increase the quality and quantity of products from horticultural species and establish an environmentally friendly practice is a reality. However, the development of research that defines the best strategies for using this technology must be carried out continuously, aiming at the best conditions for producers.

Background and aims: A recent report indicated that 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase-encoding Pseudomonas aeruginosa inhibited Arabidopsis germination. The aim of this study was to understand the role of ACC deaminase in germination arrest and evaluate the potential of ACC deaminase-encoding rhizobacteria for grass and weed control. Methods: The effect of ACC deaminase-encoding Pseudomonas putida KT2440 (1 × 107 to 5 × 109 cells/mL) on 'Nipponbare' rice germination was evaluated. In addition, the ability of KT2440 to arrest grass and weed germination was assessed in vitro and in plant-soil system. Results: KT2440 inhibited rice germination at high concentrations (> 1 × 108 cells/mL). The synthesis of the hormone ethylene was downregulated in rice seeds, whereas genes involved in the abscisic acid signaling pathway were upregulated. The mutant KT2440 formed by deleting the ACC deaminase gene had no inhibitory effect. KT2440 also inhibited the germination of crabgrass, quackgrass and Striga asiatica, among other plants studied. Crabgrass germination was reduced by 43% when KT2440 was applied in plant-soil system. Conclusions: This study provides new insights regarding the role of ACC deaminase on rhizobacteria-seed interactions. Additionally, this study reveals a new strategy for grass and weed control that may be used in particular cases. [ABSTRACT FROM AUTHOR]

Pierce's disease is a major threat to grapevines caused by the bacterium Xylella fastidiosa. Although devoid of a type 3 secretion system commonly employed by bacterial pathogens to deliver effectors inside host cells, this pathogen is able to influence host parenchymal cells from the xylem lumen by secreting a battery of hydrolytic enzymes. Defining the cellular and biochemical changes induced during disease can foster the development of novel therapeutic strategies aimed at reducing the pathogen fitness and increasing plant health. To this end, we investigated the transcriptional, proteomic, and metabolomic responses of diseased Vitis vinifera compared to healthy plants. We found that several antioxidant strategies were induced, including the accumulation of gamma-aminobutyric acid (GABA) and polyamine metabolism, as well as iron and copper chelation, but these were insufficient to protect the plant from chronic oxidative stress and disease symptom development. Notable upregulation of phytoalexins, pathogenesis-related proteins, and various aromatic acid metabolites was part of the host responses observed. Moreover, upregulation of various cell wall modification enzymes followed the proliferation of the pathogen within xylem vessels, consistent with the intensive thickening of vessels' secondary walls observed by magnetic resonance imaging. By interpreting the molecular profile changes taking place in symptomatic tissues, we report a set of molecular markers that can be further explored to aid in disease detection, breeding for resistance, and developing therapeutics.

The problem of phosphorus and nitrogen deficiency in agricultural soils has been solved by adding chemical fertilizers. However, their excessive use and their accumulation have only contributed to environmental contamination. Given the high content of nutrients in biosolids collected from a food industry waste treatment plant, their use as fertilizers was investigated in Zea mays plants grown in sandy loam soil collected from a semi-desert area. These biosolids contained insoluble phosphorus sources; therefore, given the ability of Azotobacter nigricans to solubilize phosphates, this strain was incorporated into the study. In vitro, the suitable conditions for the growth of Z. mays plants were determined by using biosolids as a fertilizer and A. nigricans as a plant-growth-promoting microorganism; in vitro, the ability of A. nigricans to solubilize phosphates, fix nitrogen, and produce indole acetic acid, a phytohormone that promotes root formation, was also evaluated. At the greenhouse stage, the Z. mays plants fertilized with biosolids at concentrations of 15 and 20% (v/w) and inoculated with A. nigricans favored the development of bending strength plants, which was observed on the increased stem diameter (>13.5% compared with the negative control and >7.4% compared with the positive control), as well as a better absorption of phosphorus and nitrogen, the concentration of which increased up to 62.8% when compared with that in the control treatments. The interactions between plants and A. nigricans were observed via scanning electron microscopy. The application of biosolids and A. nigricans in Z. mays plants grown in greenhouses presented better development than when Z. mays plants were treated with a chemical fertilizer. The enhanced plant growth was attributed to the increase in root surface area.

The use of biological inputs is an interesting approach to optimize crop production and reduce the use of chemical inputs. Understanding the chemical communication between bacteria and plants is critical to optimizing this approach. Recently, we have shown that Sphingomonas (S.) sediminicola can improve both nitrogen supply and yield in pea. Here, we used biochemical methods and untargeted metabolomics to investigate the chemical dialog between S. sediminicola and pea. We also evaluated the metabolic capacities of S. sediminicola by metabolic profiling. Our results showed that peas release a wide range of hexoses, organic acids, and amino acids during their development, which can generally recruit and select fast-growing organisms. In the presence of S. sediminicola, a more specific pattern of these molecules took place, gradually adapting to the metabolic capabilities of the bacterium, especially for pentoses and flavonoids. In turn, S. sediminicola is able to produce several compounds involved in cell differentiation, biofilm formation, and quorum sensing to shape its environment, as well as several molecules that stimulate pea growth and plant defense mechanisms.

Copper (Cu) is an essential element that can be toxic if homeostasis is disrupted. Xylella fastidiosa. 'a xylem - limited plant pathogenic bacte-inocularium that causes disease in many economically important crops world - wide. has been exposed to Cu stress caused by wide application of Cu-containing antimicrobials used to control other diseases. However. X fastidiosa Eu homeostasis mechanisms are still poorly understood. The potentially Cu - related protein CutC, which is involved in Cu tolerance iii Escherichia coli and humans, has not been analyzed functionally in plant pathogenic bacteria. We demonstrate that recombinantly expressed X faslidiosa Cute binds Cu and deletion of CutC gene( PD0586) iii X. fas·-lidiI )Sct showed increased sensitivity to Cu - shock compared with wild type( WT) strain TemeculaL. When infecting plants in the greenhouse. CltiC mutant showed deci ·eased disease incidence and severity compated with WT but adding Cu exaggerated severity. Interestingly, the inocularium tion of ClaC mutant caused reduced symptoms in the acropetal regions of plants. We hypothesize that X fastidiosa cute is involved in Cu homeostasis by binding Cu in cells, leading to Cu detoxification, which is crucial to withstand Cu - shock stress. Unveiling the role of cutC gene in X. fastidiosa facilitates further understanding of Cu homeostasis iii bacterial pathogens . [ABSTRACT FROM AUTHOR]

The composition and structure of the rhizosphere microbiome is affected by many factors, including soil type, genotype, and cultivation time of the plant. However, the interaction mechanisms among these factors are largely unclear. We use culture-independent 16S rRNA amplicon sequencing to investigate the rhizosphere bacterial composition and the structure of cultivated cucumber Xintaimici (XT) and wild-type cucumber Cucumis sativus var. hardwickii (HD) in four kinds of soils. We found that soil type, cultivation time, and genotype affected the composition and structure of cucumber rhizosphere bacterial communities. Notably, HD showed better physiological features in sandy soil and sandy loam soil than it did in black soil and farm soil at 50 days post-sowing, which was due to its stronger recruitment ability to Nitrospira , Nocardioides , Bacillus , and Gaiella in sandy soil, and more Tumebacillus , Nitrospira , and Paenibacillus in sandy loam soil. Meanwhile, we also found that HD showed a better recruiting capacity for these bacterial genera than XT in both sandy soil and sandy loam soil. Functional predictions indicated that these bacteria might have had stronger root colonization ability and then promoted the growth of cucumbers by enhancing nitrogen metabolism and active metabolite secretion. In this study, our findings provided a better insight into the relationship between cucumber phenotype, genotype, and the rhizosphere bacterial community, which will offer valuable theoretical references for rhizosphere microbiota studies and its future application in agriculture. [ABSTRACT FROM AUTHOR]

Neonicotinoids (NEOs) are the most widely used insecticides in the world and pose a serious threat to aquatic ecosystems. The combined use of free-floating aquatic plants and associated microorganisms has a tremendous potential for remediating water contaminated by pesticides. The aim of this study was to determine whether plant growth-promoting bacteria (PGPB) could enhance the phytoremediation efficiency of duckweed (Lemna aequinoctialis) in NEO-contaminated water. A total of 18 different bacteria were isolated from pesticide-stressed agricultural soil. One of the isolates, Pseudomonas monteilii FC02, exhibited an excellent ability to promote duckweed growth and was selected for the NEO removal experiment. The influence of strain FC02 inoculation on the accumulation of three typical NEOs (dinotefuran, thiacloprid, and imidaclothiz) in plant tissues, the removal efficiency in water, and plant growth parameters were evaluated during the 14-day experimental period. The results showed that strain FC02 inoculation significantly (p < 0.05) increased plant biomass production and NEO accumulation in plant tissues. The maximum NEO removal efficiencies were observed in the inoculated duckweed treatment after 14 days, with 92.23, 87.75, and 96.42% for dinotefuran, thiacloprid, and imidaclothiz, respectively. This study offers a novel view on the bioremediation of NEOs in aquatic environments by a PGPB–duckweed partnership. [ABSTRACT FROM AUTHOR]

The composition and structure of the rhizosphere microbiome is affected by many factors, including soil type, genotype, and cultivation time of the plant. However, the interaction mechanisms among these factors are largely unclear. We use culture-independent 16S rRNA amplicon sequencing to investigate the rhizosphere bacterial composition and the structure of cultivated cucumber Xintaimici (XT) and wild-type cucumber Cucumis sativus var. hardwickii (HD) in four kinds of soils. We found that soil type, cultivation time, and genotype affected the composition and structure of cucumber rhizosphere bacterial communities. Notably, HD showed better physiological features in sandy soil and sandy loam soil than it did in black soil and farm soil at 50 days post-sowing, which was due to its stronger recruitment ability to Nitrospira, Nocardioides, Bacillus, and Gaiella in sandy soil, and more Tumebacillus, Nitrospira, and Paenibacillus in sandy loam soil. Meanwhile, we also found that HD showed a better recruiting capacity for these bacterial genera than XT in both sandy soil and sandy loam soil. Functional predictions indicated that these bacteria might have had stronger root colonization ability and then promoted the growth of cucumbers by enhancing nitrogen metabolism and active metabolite secretion. In this study, our findings provided a better insight into the relationship between cucumber phenotype, genotype, and the rhizosphere bacterial community, which will offer valuable theoretical references for rhizosphere microbiota studies and its future application in agriculture.

Neonicotinoids (NEOs) are the most widely used insecticides in the world and pose a serious threat to aquatic ecosystems. The combined use of free-floating aquatic plants and associated microorganisms has a tremendous potential for remediating water contaminated by pesticides. The aim of this study was to determine whether plant growth-promoting bacteria (PGPB) could enhance the phytoremediation efficiency of duckweed (Lemna aequinoctialis) in NEO-contaminated water. A total of 18 different bacteria were isolated from pesticide-stressed agricultural soil. One of the isolates, Pseudomonas monteilii FC02, exhibited an excellent ability to promote duckweed growth and was selected for the NEO removal experiment. The influence of strain FC02 inoculation on the accumulation of three typical NEOs (dinotefuran, thiacloprid, and imidaclothiz) in plant tissues, the removal efficiency in water, and plant growth parameters were evaluated during the 14-day experimental period. The results showed that strain FC02 inoculation significantly (p

In plants, aldoximes per se act as defense compounds and are precursors of complex defense compounds such as cyanogenic glucosides and glucosinolates. Bacteria rarely produce aldoximes, but some are able to transform them by aldoxime dehydratase (Oxd), followed by nitrilase (NLase) or nitrile hydratase (NHase) catalyzed transformations. Oxds are often encoded together with NLases or NHases in a single operon, forming the aldoxime–nitrile pathway. Previous reviews have largely focused on the use of Oxds and NLases or NHases in organic synthesis. In contrast, the focus of this review is on the contribution of these enzymes to plant-bacteria interactions. Therefore, we summarize the substrate specificities of the enzymes for plant compounds. We also analyze the taxonomic and ecological distribution of the enzymes. In addition, we discuss their importance in selected plant symbionts. The data show that Oxds, NLases, and NHases are abundant in Actinobacteria and Proteobacteria. The enzymes seem to be important for breaking through plant defenses and utilizing oximes or nitriles as nutrients. They may also contribute, e.g., to the synthesis of the phytohormone indole-3-acetic acid. We conclude that the bacterial and plant metabolism of aldoximes and nitriles may interfere in several ways. However, further in vitro and in vivo studies are needed to better understand this underexplored aspect of plant-bacteria interactions. [ABSTRACT FROM AUTHOR]

Plant roots exude a wide variety of secondary metabolites able to attract and/or control a large diversity of microbial species. In return, among the root microbiota, some bacteria can promote plant development. Among these, Pseudomonas are known to produce a wide diversity of secondary metabolites that could have biological activity on the host plant and other soil microorganisms. We previously showed that wheat can interfere with Pseudomonas secondary metabolism production through its root metabolites. Interestingly, production of Pseudomonas bioactive metabolites, such as phloroglucinol, phenazines, pyrrolnitrin, or acyl homoserine lactones, are modified in the presence of wheat root extracts. A new cross metabolomic approach was then performed to evaluate if wheat metabolic interferences on Pseudomonas secondary metabolites production have consequences on wheat metabolome itself. Two different Pseudomonas strains were conditioned by wheat root extracts from two genotypes, leading to modification of bacterial secondary metabolites production. Bacterial cells were then inoculated on each wheat genotypes. Then, wheat root metabolomes were analyzed by untargeted metabolomic, and metabolites from the Adular genotype were characterized by molecular network. This allows us to evaluate if wheat differently recognizes the bacterial cells that have already been into contact with plants and highlights bioactive metabolites involved in wheat—Pseudomonas interaction. [ABSTRACT FROM AUTHOR]

Here, we estimate fast changes in the fluidity of Sinorhizobium meliloti membranes submitted to cyclic temperature changes (10°C–40°C–10°C) by monitoring the fluorescence polarization (P) of DPH and TMA-DPH of the whole cell (WC) as well as in its outer (OM) and inner (IM) membranes. Additionally, the long-term response to thermal changes is demonstrated through the dynamics of the phospholipid and fatty acid composition in each membrane. This allowed membrane homeoviscous adaptation by the return to optimal fluidity levels as measured by the PDPH/TMA-DPH in WC, OM, IM, and multilamellar vesicles of lipids extracted from OM and IM. Due to probe-partitioning preferences and membranes' compositional characteristics, DPH and TMA-DPH exhibit different behaviors in IM and OM. The rapid effect of cyclic temperature changes on the P was the opposite in both membranes with the IM being the one that exhibited the thermal behavior expected for lipid bilayers. Interestingly, only after the incubation at 40°C, cells were unable to recover the membrane preheating P levels when cooled up to 10°C. Solely in this condition, the formation of threads and nodular structures in Medicago sativa infected with S. meliloti were delayed, indicating that the symbiotic interaction was partially altered but not halted. [ABSTRACT FROM AUTHOR]

Here, we estimate fast changes in the fluidity of Sinorhizobium meliloti membranes submitted to cyclic temperature changes (10°C–40°C–10°C) by monitoring the fluorescence polarization (P) of DPH and TMA-DPH of the whole cell (WC) as well as in its outer (OM) and inner (IM) membranes. Additionally, the long-term response to thermal changes is demonstrated through the dynamics of the phospholipid and fatty acid composition in each membrane. This allowed membrane homeoviscous adaptation by the return to optimal fluidity levels as measured by the PDPH/TMA-DPH in WC, OM, IM, and multilamellar vesicles of lipids extracted from OM and IM. Due to probe-partitioning preferences and membranes’ compositional characteristics, DPH and TMA-DPH exhibit different behaviors in IM and OM. The rapid effect of cyclic temperature changes on the P was the opposite in both membranes with the IM being the one that exhibited the thermal behavior expected for lipid bilayers. Interestingly, only after the incubation at 40°C, cells were unable to recover the membrane preheating P levels when cooled up to 10°C. Solely in this condition, the formation of threads and nodular structures in Medicago sativa infected with S. meliloti were delayed, indicating that the symbiotic interaction was partially altered but not halted.

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Heavy metal contamination is a worldwide concern and a challenge to resolve due to the toxicity poses a significant threat to all living organisms in the environment. Phytoremediation is an environmental-friendly approach to alleviate heavy metal contamination in the soil. Combining the plant and beneficial bacteria inoculant to remediate soil heavy metal is known as bacterial inoculant-assisted phytoremediation. Beneficial bacteria facilitate plant metal uptake by mobilizing the heavy metals in the soil and enhancing plant vigor. The inoculant formulations can be prepared as liquid, granules or powders. Nonetheless, the effective interaction between plant and bacteria is not promised in unsterilized soil, thus affecting the phytoremediation efficiency. The development of bacterial inoculants for phytoremediation and the effects of the inoculants in soil are overlooked in current research studies. Therefore, an ample understanding of the bacterial inoculant-assisted phytoremediation concept is pertinent to circumvent the limitations. This article discusses the relationship between beneficial bacteria inoculant and plant in different techniques of phytoremediation, recent advances in developing bacterial inoculants for phytoremediation and the fate of the inoculants in soil. The provided information in this article generates more insights on the optimization works, which ultimately leading to the possible field application. [ABSTRACT FROM AUTHOR]

Strawberry (Fragaria x ananassa, Duch.) is an important crop worldwide. However, since it is a highly demanding crop in terms of the chemical conditions of the substrate, a large part of strawberry production implies the application of large amounts of fertilizers in the production fields. This practice can cause environmental problems, in addition to increases in the fruit’s production costs. In this context, applying plant growth-promoting bacteria in production fields can be an essential strategy, especially thanks to their ability to stimulate plant growth via different mechanisms. Therefore, this study aimed to test in vitro and in vivo the potential of bacteria isolated from strawberry leaves and roots to directly promote plant growth. The isolates were tested in vitro for their ability to produce auxins, solubilize phosphate and fix nitrogen. Isolates selected in vitro were tested on strawberry plants to promote plant growth and increase the accumulation of nitrogen and phosphorus in the leaves. The tested isolates showed an effect on plant growth according to biometric parameters. Among the tested isolates, more expressive results for the studied variables were observed with the inoculation of the isolate MET12M2, belonging to the species Brevibacillus fluminis. In general, bacterial inoculation induced strain-dependent effects on strawberry growth. In vitro and in vivo assays showed the potential use of the B. fluminis MET12M2 isolate as a growth promoter for strawberries.

Mitsuaria sp. TWR114 is a biocontrol agent against tomato bacterial wilt (TBW). We aimed to gain genomic insights relevant to the biocontrol mechanisms and colonization ability of this strain. The draft genome size was found to be 5,632,523 bp, with a GC content of 69.5%, assembled into 1144 scaffolds. Genome annotation predicted a total of 4675 protein coding sequences (CDSs), 914 pseudogenes, 49 transfer RNAs, 3 noncoding RNAs, and 2 ribosomal RNAs. Genome analysis identified multiple CDSs associated with various pathways for the metabolism and transport of amino acids and carbohydrates, motility and chemotactic capacities, protection against stresses (oxidative, antibiotic, and phage), production of secondary metabolites, peptidases, quorum-quenching enzymes, and indole-3-acetic acid, as well as protein secretion systems and their related appendages. The genome resource will extend our understanding of the genomic features related to TWR114's biocontrol and colonization abilities and facilitate its development as a new biopesticide against TBW. [ABSTRACT FROM AUTHOR]

The adaptation of crops to saline stress conditions generated by changes in rainfall and the current production systems is essential for maintaining many of them and minimizing possible damage or reductions in their productivity. The use of microorganisms to improve the conditions of plants from extreme environments, increasing their resilience, appears to be a possible alternative. In this work, we isolated strains from samples obtained in extreme environments, such as the Atacama Desert and Sahara Desert, and evaluated their capacity to promote the growth of plants directly and under stress conditions. We studied their ability to grow under salinity, and we selected some of these strains for their capacity to improve plant resilience.

Bacterial transcriptome profiling in the presence of plant fluids or extracts during microbial growth may provide relevant information on plant–bacteria interactions. Here, RNA sequencing (RNA-Seq) was used to determine the transcriptomic profile of Herbaspirillum seropedicae strain HRC54 at the early stages of response to sugarcane apoplastic fluid. Differentially expressed gene (DEG) analysis was performed using the DESeq2 and edgeR packages, followed by functional annotation using Blast2GO and gene ontology enrichment analysis using the COG and KEGG databases. After 2 h of sugarcane apoplastic fluid addition to the H. seropedicae HRC54 culture, respectively, 44 and 45 genes were upregulated and downregulated. These genes were enriched in bacterial metabolism (e.g., oxidoreductase and transferase), ABC transporters, motility, secretion systems, and signal transduction. RNA-Seq expression profiles of 12 genes identified in data analyses were verified by RT-qPCR. The results suggested that H. seropedicae HRC54 recognized sugarcane apoplastic fluid as the host signal, and some DEGs were closely involved at the early stages of the establishment of plant–bacteria interactions. [ABSTRACT FROM AUTHOR]

Plant roots exude a wide variety of secondary metabolites able to attract and/or control a large diversity of microbial species. In return, among the root microbiota, some bacteria can promote plant development. Among these, Pseudomonas are known to produce a wide diversity of secondary metabolites that could have biological activity on the host plant and other soil microorganisms. We previously showed that wheat can interfere with Pseudomonas secondary metabolism production through its root metabolites. Interestingly, production of Pseudomonas bioactive metabolites, such as phloroglucinol, phenazines, pyrrolnitrin, or acyl homoserine lactones, are modified in the presence of wheat root extracts. A new cross metabolomic approach was then performed to evaluate if wheat metabolic interferences on Pseudomonas secondary metabolites production have consequences on wheat metabolome itself. Two different Pseudomonas strains were conditioned by wheat root extracts from two genotypes, leading to modification of bacterial secondary metabolites production. Bacterial cells were then inoculated on each wheat genotypes. Then, wheat root metabolomes were analyzed by untargeted metabolomic, and metabolites from the Adular genotype were characterized by molecular network. This allows us to evaluate if wheat differently recognizes the bacterial cells that have already been into contact with plants and highlights bioactive metabolites involved in wheat—Pseudomonas interaction.

The application of new agricultural technologies to attain sustainable production systems is necessary. The use of plant growth-promoting bacteria to improve plant growth and health has been studied for decades. This work aimed to isolate diazotrophic endophytic bacteria associated with sweet sorghum plants and study the interaction of their inoculation in combination with chemical N-fertilization on different sorghum cultivars. A bacterial collection of 181 isolates was constructed and characterized in vitro and in vivo. From that, the strains Enterobacter sp. UYSB89 and Kosakonia sp. UYSB139 were nifH +, produce IAA, defined as true endophytes and able to promote growth of two sweet sorghum under greenhouse conditions. The evaluated cultivars responded differentially to bacterial inoculation, the nitrogen fertilization doses and their interaction. Thus, plant growth is a multifactorial consequence of the interrelation between crop practices and the plant genotypes. This knowledge is a valuable factor in terms of understanding plant–bacteria endophyte interactions to preserve environmental sustainability during the implementation of agronomic practices. [ABSTRACT FROM AUTHOR]

The large-scale use of the herbicide glyphosate leads to growing ecotoxicological and human health concerns. Microbe-assisted phytoremediation arises as a good option to remove, contain, or degrade glyphosate from soils and waterbodies, and thus avoid further spreading to non-target areas. To achieve this, availability of plant-colonizing, glyphosate-tolerant and -degrading strains is required and at the same time, it must be linked to plant-microorganism interaction studies focusing on a substantive ability to colonize the roots and degrade or transform the herbicide. In this work, we isolated bacteria from a chronically glyphosate-exposed site in Argentina, evaluated their glyphosate tolerance using the minimum inhibitory concentration assay, their in vitro degradation potential, their plant growth-promotion traits, and performed whole genome sequencing to gain insight into the application of a phytoremediation strategy to remediate glyphosate contaminated agronomic soils. Twenty-four soil and root-associated bacterial strains were isolated. Sixteen could grow using glyphosate as the sole source of phosphorous. As shown in MIC assay, some strains tolerated up to 10000 mg kg–1 of glyphosate. Most of them also demonstrated a diverse spectrum of in vitro plant growth-promotion traits, confirmed in their genome sequences. Two representative isolates were studied for their root colonization. An isolate of Ochrobactrum haematophilum exhibited different colonization patterns in the rhizoplane compared to an isolate of Rhizobium sp. Both strains were able to metabolize almost 50% of the original glyphosate concentration of 50 mg l–1 in 9 days. In a microcosms experiment with Lotus corniculatus L, O. haematophilum performed better than Rhizobium , with 97% of glyphosate transformed after 20 days. The results suggest that L. corniculatus in combination with to O. haematophilum can be adopted for phytoremediation of glyphosate on agricultural soils. An effective strategy is presented of linking the experimental data from the isolation of tolerant bacteria with performing plant-bacteria interaction tests to demonstrate positive effects on the removal of glyphosate from soils. [ABSTRACT FROM AUTHOR]

The plant holobiont is a complex entity composed of the plant and the organisms that live in and on it including its microbiota. The plant microbiota includes, among other microorganisms, bacterial endophytes, which are bacteria that can invade living plant tissues without causing symptoms of disease. The interaction between the endophytic bacterial microbiota and their plant host has profound influences on their fitness and depends on biotic and abiotic factors. For these interactions to be established, the bacteria have to be present at the right time, in the right place either colonizing the soil or the seed. In this review we summarize the current knowledge regarding the sources of the bacterial endophytic microbiome and the processes involved in the assemblage of the resulting community during the initial stages of plant development. The adaptations that allow the spatial approximation of soil- and seed-borne bacteria towards infection and colonization of the internal tissues of plants will be addressed in this review. [ABSTRACT FROM AUTHOR]

The differences in volatile profile of Echinacea purpurea plants not-inoculated (EpC) and inoculated with their endophytes from roots (EpR) and stem/leaves (EpS/L) were analysed and compared by GC-FID/GC–MS in an in vitro model. Non-terpenes and sesquiterpene hydrocarbons were the most abundant classes with an opposite behaviour of EpS/L showing a decreased emission of sesquiterpenes and an increase of non-terpene derivatives. The main compounds obtained from EpS/L were (Z)-8-dodecen-1-ol and 1-pentadecene, while germacrene D and β-caryophyllene were the key compounds in EpC and EpR. For the first time, this work indicates that bacterial endophytes modify the aroma profiles of infected and non-infected in vitro plants of the important medicinal plant E. purpurea. Therefore, our model of infection could permit to select endophytic strains to use as biotechnological tool in the production of medicinal plants enriched in volatile bioactive compounds. [ABSTRACT FROM AUTHOR]

Bacteria that positively interact with plant roots are defined as plant growth promoting rhizobacteria (PGPR). Although the positive effect of PGPR on plant growth has been widely studied, their impact on genetic regulation during plant growth processes remains largely unknown. Therefore, this study aimed to gain a deeper understanding of the regulatory role of miRNA and redox enzymes in response to PGPR at the maize seedling stage in leaf growth zone which consists of the meristem, elongation and mature zones. For this purpose, growth of the third leaf was monitored in response to Pseudomonas putida (P. putida) KT2440 at phenotypic, physiological, cellular, kinematic, and transcriptional levels. This application resulted in an increase of 15% in shoot length, 56% in both shoot fresh/dry weight, 10% in chlorophyll amount, 8% in mature cell length, 15% in leaf elongation rate, and 7% in cell production; meanwhile final leaf length was unchanged, while leaf area and leaf width decreased by 22% and 16%, respectively. Ascorbate peroxidase and glutathione reductase activity increased throughout the leaf growth zone indicating a possible role in PGPR-plant interaction during transition between cell division, expansion and differentiation processes. The expression analysis of cell cycle check point marker genes revealed that CycA2_1 was mainly responsible for promoting cell proliferation in meristem. miR160, miR169 and miR408 were differentially expressed in the meristem, indicating their indirect regulatory roles in the cell division response to PGPR. In addition, miR160, miR319 and miR396 were downregulated in the elongation zone, which draws attention to their possible role in regulating cell elongation processes. In summary, cell cycle, redox and miRNA regulation in maize seedling growth zones in response to P. putida were investigated for the first time in this study. [ABSTRACT FROM AUTHOR]

Although rice is one of the most cultivated, consumed, and essential crops worldwide, it is highly susceptible to a wide range of bacterial and fungal pathogens that significantly reduce the production and quality of rice. Recently, our research group reported that the plant growth‐promoting rhizobacterium Lysobacter gummosus OH17 was able to enhance the ethylene levels in Oryza sativa 'Nipponbare' plants at the late interaction stages. In this work, L. gummosus OH17 was found to be capable of inducing the overexpression of relevant genes of the jasmonic acid and ethylene transduction pathways in Nipponbare plants, such as OsACC, OsACO, OsERF3, and OsLOX, which resulted in the up‐regulation of a number of pathogenesis‐related proteins. The observed metabolic effects enhanced the disease resistance of rice against the three most devastating rice pathogens: Magnaporthe oryzae causing rice blast, Rhizoctonia solani causing rice sheath blight, and Xanthomonas oryzae pv. oryzae causing bacterial leaf blight. Furthermore, it was shown that L. gummosus OH17 also enhanced ethylene production levels in other O. sativa varieties from both the japonica and indica subspecies. Here, we report for the first time the metabolic alterations produced by plant growth‐promoting rhizobacterium L. gummosus OH17 at the late interaction stages and how these alterations induce systemic resistance. [ABSTRACT FROM AUTHOR]

Aims: We evaluated the effect of Azospirillum brasilense strain HM053 inoculation on maize seeds, a spontaneous mutant that excrete ammonium and fix nitrogen constitutively. Methods: Maize was grown with different nitrogen (urea) concentration and inoculated with A. brasilense Ab-V5 (Brazilian commercial strain) or HM053 strain in four field experiments, in three regions of Parana State, Southern Brazil. We evaluated yield components, nutrient content on leaves and grains and productivity during the crop cycle. Results: Inoculation with A. brasilense strain Ab-V5 and HM053 associated with base fertilization (30 kg ha−1 N) improved crop yield in all trials. Ab-V5 increased production between 2.2 to 10.4%, or 178.0 to 759.9 kg ha−1, respectively. HM053, by itself, increased production between 4.7 to 29%, or 460.5 to 1769.3 kg ha−1, respectively. Conclusion: The new strain HM053 showed to be a great biofertilizer for maize seeds and a new alternative for a more sustainable agriculture. [ABSTRACT FROM AUTHOR]

Due to the increase in both human population growth and environmental pressure, it is necessary to raise agricultural productivity without enhancing environmental footprint. Within this context, soil inoculation with PGPB (Plant Growth Promoting Bacteria) may be considered a promising tool of integrated management systems. In particular, PGPB may improve plant growth either directly, by facilitating resource use or modulating plant hormone levels, or indirectly by decreasing the inhibitory effects of various pathogenic agents. PGPB comprise different functional and taxonomic groups of bacteria like Pseudomonas, Bacillus, Rhizobium and others. Their ability to either mobilize mineral or organic bound nutrients from the pedosphere or to fix atmospheric N2 and make it available to the plants, is a crucial feature in their application. In literature some data are available on the use of commercial PGPB, while less efforts have been made on the study of the effect of autochthonous PGPB isolated from soils on sustainability of cropping systems; thus a literature survey on these aspects was carried out with special focus on wheat, a staple food for a large part of world population. In particular, the main topic of this review is the potential of PGPB to enhance use efficiency of agro-environmental resources focusing on the interaction PGPB-wheat for improving nitrogen use efficiency.