Efficiency of organomineral fertilizer and doses of Azospirillum brasilense on the morphophysiological quality of Mezilaurus itauba seedlings.

The present study was conducted to determine the efficiency of organomineral fertilizer from cupuaçu residues (ORFCup) and dose of maximum technical efficiency of Azospirillum brasilense on the initial growth and morphophysiological quality of Mezilaurus itauba seedlings in the northern Amazon. The variables evaluated were: shoot height (H, cm), stem diameter (SD, mm), shoot dry mass (SDM, g plant-1), root dry mass (RDM, g plant-1) total dry mass (TDM, g plant-1), Dickson quality index (DQI), net assimilation rate (NAR, g m-2 day-1), leaf relative growth rate (RGR, g m-2 day-1), leaf area ratio (LAR, m2 g-1), leaf relative growth rate (RGR, g m-2 day-1), leaf area ratio (LAR, m2 g-1), specific leaf area (SLA, cm2 g-1), and leaf mass ratio (LMR, g g-1). Organomineral fertilizer from cupuaçu residues promotes better quality and robustness in M. itauba seedlings at the dose of maximum technical efficiency of 0.45 mL. L-1 of A. brasilense.

Investigating the synergistic effects of biochar, trans-zeatin riboside, and Azospirillum brasilense on soil improvement and enzymatic activity in water-stressed wheat.

BACKGROUND: Water stress is a major danger to crop yield, hence new approaches to strengthen plant resilience must be developed. To lessen the negative effects of water stress on wheat plants, present study was arranged to investigate the role of synergistic effects of biochar, trans-zeatin riboside (t-ZR), and Azospirillum brasilense on soil improvement and enzymatic activity in water-stressed wheat. RESULTS: In a three-replication experiment comprising of four treatments (T0: Control, T1: Drought stress (DS), T2: DS + t-ZR with biochar, T3: DS + A. brasilense with biochar), we observed notable improvements in soil quality and enzymatic activities in water-stressed wheat plants with the application of t-ZR and A. brasilense with biochar. In drought stress, Treatment having the application of A. brasilense with biochar performs best as compared to the other and significant increased the enzymatic activities such as peroxidase (7.36%), catalase (8.53%), superoxide dismutase (6.01%), polyphenol oxidase (14.14%), and amylase (16.36%) in wheat plants. Different enzymatic activities showed different trends of results. Soil organic C, dissolved organic C, dissolved organic N also enhanced 29.46%, 8.59%, 22.70% respectively with the application of A. brasilense with biochar under drought stress condition. CONCLUSIONS: The synergistic action of A. brasilense and biochar creates an effective microbiological environment that supports essential plant physiological processes during drought stress. This enhancement is attributed to improved soil fertility and increased organic matter content, highlighting the potential of these novel strategies in mitigating water stress effects and enhancing crop resilience.

Chemotactic Interactions of Scenedesmus sp. and Azospirillum brasilense Investigated by Microfluidic Methods.

The use of algae for industrial, biotechnological, and agricultural purposes is spreading globally. Scenedesmus species can play an essential role in the food industry and agriculture due to their favorable nutrient content and plant-stimulating properties. Previous research and the development of Scenedesmus-based foliar fertilizers raised several questions about the effectiveness of large-scale algal cultivation and the potential effects of algae on associative rhizobacteria. In the microbiological practice applied in agriculture, bacteria from the genus Azospirillum are one of the most studied plant growth-promoting, associative, nitrogen-fixing bacteria. Co-cultivation with Azospirillum species may be a new way of optimizing Scenedesmus culturing, but the functioning of the co-culture system still needs to be fully understood. It is known that Azospirillum brasilense can produce indole-3-acetic acid, which could stimulate algae growth as a plant hormone. However, the effect of microalgae on Azospirillum bacteria is unclear. In this study, we investigated the behavior of Azospirillum brasilense bacteria in the vicinity of Scenedesmus sp. or its supernatant using a microfluidic device consisting of physically separated but chemically coupled microchambers. Following the spatial distribution of bacteria within the device, we detected a positive chemotactic response toward the microalgae culture. To identify the metabolites responsible for this behavior, we tested the chemoeffector potential of citric acid and oxaloacetic acid, which, according to our HPLC analysis, were present in the algae supernatant in 0.074 mg/ml and 0.116 mg/ml concentrations, respectively. We found that oxaloacetic acid acts as a chemoattractant for Azospirillum brasilense.

Metabolic and physiological adaptations of microalgal growth-promoting bacterium Azospirillum brasilense growing under biogas atmosphere: a microarray-based transcriptome analysis.

Using microalgal growth-promoting bacteria (MGPB) to improve the cultured microalga metabolism during biotechnological processes is one of the most promising strategies to enhance their benefits. Nonetheless, the culture condition effect used during the biotechnological process on MGPB growth and metabolism is key to ensure the expected positive bacterium growth and metabolism of microalgae. In this sense, the present research study investigated the effect of the synthetic biogas atmosphere (75% CH4-25% CO2) on metabolic and physiological adaptations of the MGPB Azospirillum brasilense by a microarray-based transcriptome approach. A total of 394 A. brasilense differentially expressed genes (DEGs) were found: 201 DEGs (34 upregulated and 167 downregulated) at 24 h and 193 DEGs (140 upregulated and 53 downregulated) under the same conditions at 72 h. The results showed a series of A. brasilense genes regulating processes that could be essential for its adaptation to the early stressful condition generated by biogas. Evidence of energy production is shown by nitrate/nitrite reduction and activation of the hypothetical first steps of hydrogenotrophic methanogenesis; signal molecule modulation is observed: indole-3-acetic acid (IAA), riboflavin, and vitamin B6, activation of Type VI secretion system responding to IAA exposure, as well as polyhydroxybutyrate (PHB) biosynthesis and accumulation. Moreover, an overexpression of ipdC, ribB, and phaC genes, encoding the key enzymes for the production of the signal molecule IAA, vitamin riboflavin, and PHB production of 2, 1.5 and 11 folds, respectively, was observed at the first 24 h of incubation under biogas atmosphere Overall, the ability of A. brasilense to metabolically adapt to a biogas atmosphere is demonstrated, which allows its implementation for generating biogas with high calorific values and the use of renewable energies through microalga biotechnologies.

Plant seedlings of peas, tomatoes, and cucumbers exude compounds that are needed for growth and chemoattraction of Rhizobium leguminosarum bv. viciae 3841 and Azospirillum brasilense Sp7.

This study characterizes seedling exudates of peas, tomatoes, and cucumbers at the level of chemical composition and functionality. A plant experiment confirmed that Rhizobium leguminosarum bv. viciae 3841 enhanced growth of pea shoots, while Azospirillum brasilense Sp7 supported growth of pea, tomato, and cucumber roots. Chemical analysis of exudates after 1 day of seedling incubation in water yielded differences between the exudates of the three plants. Most remarkably, cucumber seedling exudate did not contain detectable sugars. All exudates contained amino acids, nucleobases/nucleosides, and organic acids, among other compounds. Cucumber seedling exudate contained reduced glutathione. Migration on semi solid agar plates containing individual exudate compounds as putative chemoattractants revealed that R. leguminosarum bv. viciae was more selective than A. brasilense, which migrated towards any of the compounds tested. Migration on semi solid agar plates containing 1:1 dilutions of seedling exudate was observed for each of the combinations of bacteria and exudates tested. Likewise, R. leguminosarum bv. viciae and A. brasilense grew on each of the three seedling exudates, though at varying growth rates. We conclude that the seedling exudates of peas, tomatoes, and cucumbers contain everything that is needed for their symbiotic bacteria to migrate and grow on.

Maize-Azospirillum brasilense interaction: accessing maize's miRNA expression under the effect of an inhibitor of indole-3-acetic acid production by the plant.

MicroRNA (miRNA) is a class of non-coding RNAs. They play essential roles in plants' physiology, as in the regulation of plant development, response to biotic and abiotic stresses, and symbiotic processes. This work aimed to better understand the importance of maize's miRNA during Azospirillum-plant interaction when the plant indole-3-acetic acid (IAA) production was inhibited with yucasin, an inhibitor of the TAM/YUC pathway. Twelve cDNA libraries from a previous Dual RNA-Seq experiment were used to analyze gene expression using a combined analysis approach. miRNA coding genes (miR) and their predicted mRNA targets were identified among the differentially expressed genes. Statistical differences among the groups indicate that Azospirillum brasilense, yucasin, IAA concentration, or all together could influence the expression of several maize's miRNAs. The miRNA's probable targets were identified, and some of them were observed to be differentially expressed. Dcl4, myb122, myb22, and morf3 mRNAs were probably regulated by their respective miRNAs. Other probable targets were observed responding to the IAA level, the bacterium, or all of them. A. brasilense was able to influence the expression of some maize's miRNA, for example, miR159f, miR164a, miR169j, miR396c, and miR399c. The results allow us to conclude that the bacterium can influence directly or indirectly the expression of some of the identified mRNA targets, probably due to an IAA-independent pathway, and that they are somehow involved in the previously observed physiological effects.

Azospirillum isscasi sp. nov., a bacterium isolated from rhizosphere soil of rice.

A Gram-negative and rod-shaped bacterium, designated C340-1T, was isolated and screened from paddy soil in Zhongshan County, Guangxi Province, PR China. This strain grew at 20-42 °C (optimum, 37 °C), pH 5.0-9.0 (optimum, pH 7.0) and 0-4 % (w/v) NaCl (optimum, 0-1 %) on Reasoner's 2A medium. The strain could fix atmospheric nitrogen and acetylene reduction activity was recorded up to 120.26 nmol ethylene h-1 (mg protein)-1. Q-10 was the only isoprenoid quinone component; phosphatidylethanolamine, phosphatidylglycerol, phosphatidylcholine, an unidentified aminolipid and an unidentified polar lipid were the major polar lipids. Summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c) and summed feature 3 (C16 : 1 ω7c and/or C16 : 1 ω6c) were the primary cellular fatty acids. The genome of strain C340-1T was 6.18 Mb, and the G+C content was 69.0 mol%. Phylogenetic tree analysis based on 16S rRNA gene and 92 core genes showed that strain C340-1T was closely related to and clustered with the type strains Azospirillum brasilense JCM 1224T, Azospirillum argentinense Az39T, Azospirillum baldaniorum Sp245T and Azospirillum formosense JCM 17639T. The average nucleotide identity (ANI), average amino acid identity (AAI) and digital DNA-DNA hybridization (dDDH) values between strain C340-1T and the closely related type strains mentioned above were significantly lower than the threshold values for species classification (95-96 %, 95-96 % and 70 %, respectively). Based on phylogenetic, genomic, phenotypic, physiological and biochemical data, we have reason to believe that C340-1T represents a new species of the genus Azospirillum, for which the name Azospirillum isscasi sp. nov. is proposed. The type strain is C340-1T(=CCTCC AB 2023105T=KCTC 8126T).

Synergic association of the consortium Arthrospira maxima with the microalga growth-promoting bacterium Azospirillum cultured under the stressful biogas composition.

The present study evaluates the association of the blue-green microalga Arthrospira maxima (Spirulina), which is known for its CO2 fixation, biomass, and high-value metabolite production, with the microalga growth-promoting bacterium Azospirillum brasilense under the stressful composition of biogas. The results demonstrated that A. maxima co-cultured with A. brasilense under the high CO2 (25%) and methane (CH4; 75%) concentrations of biogas recorded a CO2 fixation rate of 0.24 ± 0.03 g L-1 days-1, thereby attaining a biomass production of 1.8 ± 0.03 g L-1. Similarly, the biochemical composition quality of this microalga enhanced the attainment of higher contents of carbohydrates, proteins, and phycocyanin than cultured alone. However, metabolites other than tryptophan (Trp) and indole-3-acetic acid could have supported this beneficial interaction. Overall, the results demonstrate that this prokaryotic consortium of A. maxima-A. brasilense established a synergic association under biogas, which represents a sustainable strategy to improve the bio-refinery capacity of this microalga and increase the usefulness of A. brasilense in multiple economic sectors.

Nitrogen metabolism in maize plants submitted to drought, brassinosteroids and azospirillum.

The water deficit in particular, reduces the productivity of vegetable crops. To minimize these harmful effects on agriculture, several agronomic and physiological practices are being studied, such as the use of bacteria and water stress attenuators, such as brassinosteroids. Considering the socioeconomic relevance of corn culture and its sensitivity when exposed to water deficit, the objective of the present study was to evaluate the action of brassinosteroids and azospirillum on nitrogen metabolism in corn plants subjected to water stress conditions. The experiment was carried out in a greenhouse, in a period of 47 days, with corn plants, using the hybrid K9606 VIP3. The design was completely randomized, in a 2x2x3 factorial scheme, with six replications. The first factor corresponds to two water regimes (presence and absence of water deficit). The second corresponds to inoculation via seed of Azospirillum brasiliense and absence of inoculation. And the third corresponds to the application of three concentrations of brassinosteroids (0, 0.3 and 0.6 µM). Were determined Nitrate; nitrate reductase; free ammonium; total soluble aminoacids; soluble proteins; proline; glycine betaine and glutamine synthetase. The lack of water in plants provided a reduction in the protein and nitrate reductase contents, in leaves and roots. For ammonium, plants with water deficit inoculated at a concentration of 0.3 µM, obtained an increase of 7.16 (70.26%) and 13.89 (77.04%) mmol NH4 + .Kg-1. DM (Dry mass) on the leaf and root respectively. The water deficit in the soil provided significant increases in the concentrations of glycine betaine, nitrate, proline and aminoacids, both in the leaves and in the roots of the corn plants. On the other hand, the contents of glutamine synthetase had a reduction in both leaves and roots.

Alleviation of chromium toxicity in mung bean (Vigna radiata L.) using salicylic acid and Azospirillum brasilense.

BACKGROUND: Chromium (Cr) contamination in soil poses a serious hazard because it hinders plant growth, which eventually reduces crop yield and raises the possibility of a food shortage. Cr's harmful effects interfere with crucial plant functions like photosynthesis and respiration, reducing energy output, causing oxidative stress, and interfering with nutrient intake. In this study, the negative effects of Cr on mung beans are examined, as well as investigate the effectiveness of Azospirillum brasilense and salicylic acid in reducing Cr-induced stress. RESULTS: We investigated how different Cr levels (200, 300, and 400 mg/kg soil) affected the growth of mung bean seedlings with the use of Azospirillum brasilense and salicylic acid. Experiment was conducted with randomized complete block design with 13 treatments having three replications. Significant growth retardation was caused by Cr, as were important factors like shoot and root length, plant height, dry weight, and chlorophyll content significantly reduced. 37.15% plant height, 71.85% root length, 57.09% chlorophyll contents, 82.34% crop growth rate was decreased when Cr toxicity was @ 50 µM but this decrease was remain 27.80%, 44.70%, 38.97% and 63.42%, respectively when applied A. brasilense and Salicylic acid in combine form. Use of Azospirillum brasilense and salicylic acid significantly increased mung bean seedling growth (49%) and contributed to reducing the toxic effect of Cr stress (34% and 14% in plant height, respectively) due to their beneficial properties in promoting plant growth. CONCLUSIONS: Mung bean seedlings are severely damaged by Cr contamination, which limits their growth and physiological characteristics. Using Azospirillum brasilense and salicylic acid together appears to be a viable way to combat stress brought on by Cr and promote general plant growth. Greater nutrient intake, increased antioxidant enzyme activity, and greater root growth are examples of synergistic effects. This strategy has the ability to reduce oxidative stress brought on by chromium, enhancing plant resistance to adverse circumstances. The study offers new perspectives on sustainable practices that hold potential for increasing agricultural output and guaranteeing food security.

Chromosomal gene of hybrid multisensor histidine kinase is involved in motility regulation in the rhizobacterium Azospirillum baldaniorum Sp245 under mechanical and water stress.

Azospirillum alphaproteobacteria, which live in the rhizosphere of many crops, are used widely as biofertilizers. Two-component signal transduction systems (TCSs) mediate the bacterial perception of signals and the corresponding adjustment of behavior facilitating the adaptation of bacteria to their habitats. In this study, we obtained the A. baldaniorum Sp245 mutant for the AZOBR_150176 gene, which encodes the TCS of the hybrid histidine kinase/response sensory regulator (HSHK-RR). Inactivation of this gene affected bacterial morphology and motility. In mutant Sp245-HSHKΔRR-Km, the cells were still able to synthesize a functioning polar flagellum (Fla), were shorter than those of strain Sp245, and were impaired in aerotaxis, elaboration of inducible lateral flagella (Laf), and motility in semiliquid media. The mutant showed decreased transcription of the genes encoding the proteins of the secretion apparatus, which ensures the assembly of Laf, Laf flagellin, and the repressor protein of translation of the Laf flagellin's mRNA. The study examined the effects of polyethylene glycol 6000 (PEG 6000), an agent used to simulate osmotic stress and drought conditions. Under osmotic stress, the mutant was no longer able to use collective motility in semiliquid media but formed more biofilm biomass than did strain Sp245. Introduction into mutant cells of the AZOBR_150176 gene as part of an expression vector led to recovery of the lost traits, including those mediating bacterial motility under mechanical stress induced by increased medium density. The results suggest that the HSHK-RR under study modulates the response of A. baldaniorum Sp245 to mechanical and osmotic/water stress.

Acetylene Reduction Assay: A Measure of Nitrogenase Activity in Plants and Bacteria.

Nitrogen is one of the most abundant elements in the biosphere, but its gaseous form is not biologically available to many organisms, including plants and animals. Diazotrophic microorganisms can convert atmospheric nitrogen into ammonia, a form that can be absorbed by plants in a process called biological nitrogen fixation (BNF). BNF is catalyzed by the enzyme nitrogenase, which not only reduces N2 to NH3 , but also reduces other substrates such as acetylene. The acetylene reduction assay (ARA) can be used to measure nitrogenase activity in diazotrophic organisms, either in symbiotic associations or in their free-living state. The technique uses gas chromatography to measure the reduction of acetylene to ethylene by nitrogenase in a simple, quick, and inexpensive manner. Here, we demonstrate how to: prepare nodulated soybean plants and culture free-living Azospirillum brasilense for the ARA, use the gas chromatograph to detect the ethylene formed, and calculate the nitrogenase activity based on the peaks generated by the chromatograph. The methods shown here using example organisms can be easily adapted to other nodulating plants and diazotrophic bacteria. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Acetylene reduction assay in root nodules Basic Protocol 2: Acetylene reduction assay using diazotrophic bacteria Basic Protocol 3: Calculation of nitrogenase activity Support Protocol 1: Production of acetylene from calcium carbide Support Protocol 2: Calibration of the gas chromatograph Support Protocol 3: Total protein quantification.

Azospirillum brasilense AerC and Tlp4b Cytoplasmic Chemoreceptors Are Promiscuous and Interact with the Two Membrane-Bound Chemotaxis Signaling Clusters Mediating Chemotaxis Responses.

Chemotaxis in Bacteria and Archaea depends on the presence of hexagonal polar arrays composed of membrane-bound chemoreceptors that interact with rings of baseplate signaling proteins. In the alphaproteobacterium Azospirillum brasilense, chemotaxis is controlled by two chemotaxis signaling systems (Che1 and Che4) that mix at the baseplates of two spatially distinct membrane-bound chemoreceptor arrays. The subcellular localization and organization of transmembrane chemoreceptors in chemotaxis signaling clusters have been well characterized but those of soluble chemoreceptors remain relatively underexplored. By combining mutagenesis, microscopy, and biochemical assays, we show that the cytoplasmic chemoreceptors AerC and Tlp4b function in chemotaxis and localize to and interact with membrane-bound chemoreceptors and chemotaxis signaling proteins from both polar arrays, indicating that soluble chemoreceptors are promiscuous. The interactions of AerC and Tlp4b with polar chemotaxis signaling clusters are not equivalent and suggest distinct functions. Tlp4b, but not AerC, modulates the abundance of chemoreceptors within the signaling clusters through an unknown mechanism. The AerC chemoreceptor, but not Tlp4b, is able to traffic in and out of chemotaxis signaling clusters depending on its level of expression. We also identify a role of the chemoreceptor composition of chemotaxis signaling clusters in regulating their polar subcellular organization. The organization of chemotaxis signaling proteins as large membrane-bound arrays underlies chemotaxis sensitivity. Our findings suggest that the composition of chemoreceptors may fine-tune chemotaxis signaling not only through their chemosensory specificity but also through their role in the organization of polar chemotaxis signaling clusters. IMPORTANCE Cytoplasmic chemoreceptors represent about 14% of all chemoreceptors encoded in bacterial and archaeal genomes, but little is known about how they interact with and function in large polar assemblies of membrane-bound chemotaxis signaling clusters. Here, we show that two soluble chemoreceptors with a role in chemotaxis are promiscuous and interact with two distinct membrane-bound chemotaxis signaling clusters that control all chemotaxis responses in Azospirillum brasilense. We also found that any change in the chemoreceptor composition of chemotaxis signaling clusters alters their polar organization, suggesting a dynamic interplay between the sensory specificity of chemotaxis signaling clusters and their polar membrane organization.

Microwave resonator-based sensor system for specific antibody detection.

An antibody-detecting sensor is described that is based on a microwave electrodynamic resonator. A polystyrene film with immobilized bacteria deposited on a lithium niobate plate was placed at one end of the resonator and was used as the sensing element. The second end was electrically shorted. The frequency and depth of the reflection coefficient S11 for three resonances in the range 6.5-8.5 GHz were used as an analytical signal to examine antibody interactions with bacteria and determine the time required for cell immobilization. The sensor distinguished between situations in which bacteria interacted with specific antibodies and those in which no such interaction occurred (control). Although the cell-antibody interaction changed the frequency and depth of the second and third resonance peaks, the parameters of the first resonance peak did not change. The interaction of cells with nonspecific antibodies did not change the parameters of any of the peaks. These results are promising for use in the design of methods to detect specific antibodies, which can supplement the existing methods of antibody analysis.

Fourier Transform Infrared (FTIR) Spectroscopic Study of Biofilms Formed by the Rhizobacterium Azospirillum baldaniorum Sp245: Aspects of Methodology and Matrix Composition.

Biofilms represent the main mode of existence of bacteria and play very significant roles in many industrial, medical and agricultural fields. Analysis of biofilms is a challenging task owing to their sophisticated composition, heterogeneity and variability. In this study, biofilms formed by the rhizobacterium Azospirillum baldaniorum (strain Sp245), isolated biofilm matrix and its macrocomponents have for the first time been studied in detail, using Fourier transform infrared (FTIR) spectroscopy, with a special emphasis on the methodology. The accompanying novel data of comparative chemical analyses of the biofilm matrix, its fractions and lipopolysaccharide isolated from the outer membrane of the cells of this strain, as well as their electrophoretic analyses (SDS-PAGE) have been found to be in good agreement with the FTIR spectroscopic results.

Azospirillum brasilense AbV5/6 encapsulation in dual-crosslinked beads based on cationic starch.

The main challenge of agriculture is feeding the growing population and at the same time providing environmental sustainability. Using Azospirillum brasilense as a biofertilizer has proved to be a promising solution. However, its prevalence in soil has not been efficient due to biotic and abiotic stresses. Thus, to overcome this drawback, we encapsulated the A. brasilense AbV5 and AbV6 strains in a dual-crosslinked bead based on cationic starch. The starch was previously modified with ethylenediamine by an alkylation approach. Then, the beads were obtained by a dripping technique, crosslinking sodium tripolyphosphate with a blend containing starch, cationic starch, and chitosan. The AbV5/6 strains were encapsulated into the hydrogel beads by a swelling diffusion method followed by desiccation. Plants treated with encapsulated AbV5/6 cells showed an increase in the root length by 19 %, shoot fresh weight by 17 %, and the content of chlorophyll b by 71 %. The encapsulation of AbV5/6 strains showed to keep A. brasilense viability for at least 60 days and efficiency to promote maize growth.

Synergistic interplay between Azospirillum brasilense and exogenous signaling molecule H2S promotes Cd stress resistance and growth in pak choi (Brassica chinensis L.).

Inoculation with growth-promoting rhizobacteria inoculation and the addition of exogenous signaling molecules are two distinct strategies for improving heavy metal resistance and promoting growth in crops through several mechanisms. However, whether rhizobacteria and phyllosphere signaling molecules can act synergistically alleviate heavy metal stress and promote growth and the mechanisms underlying these effects remain unclear. Here, a novel strategy involving the co-application of growth-promoting rhizobacteria and an exogenous signaling molecule was developed to reduce cadmium (Cd) phytotoxicity and promote pak choi growth in Cd-contaminated soil. We found that the co-application of Azospirillum brasilense and hydrogen sulfide (H2S) resulted in significant improvements in shoot biomass and antioxidant enzyme content and a decline in the levels of Cd translocation factors. In addition, this co-application significantly improved pak choi Cd resistance. Furthermore, we observed a significant negative correlation between abscisic acid concentration and Cd content of pak choi and a positive correlation between H2S concentration and biomass. These findings revealed that the co-application of rhizobacteria and exogenous signaling molecules synergistically promoted the growth of vegetable crops subjected to heavy metal stress. Our results may serve as a guide for improving the food safety of crops grown in soil contaminated with heavy metals.

Differences in Exudates Between Strains of Chlorella sorokiniana Affect the Interaction with the Microalga Growth-Promoting Bacteria Azospirillum brasilense : Differences in Exudates Between Strains of Chlorella sorokiniana Affect the Interaction with the Microalga Growth-Promoting Bacteria Azospirillum brasilense.

The microalga Chlorella sorokiniana and the microalgae growth-promoting bacteria (MGPB) Azospirillum brasilense have a mutualistic interaction that can begin within the first hours of co-incubation; however, the metabolites participating in this initial interaction are not yet identified. Nuclear magnetic resonance (NMR) was used in the present study to characterize the metabolites exuded by two strains of C. sorokiniana (UTEX 2714 and UTEX 2805) and A. brasilense Cd when grown together in an oligotrophic medium. Lactate and myo-inositol were identified as carbon metabolites exuded by the two strains of C. sorokiniana; however, only the UTEX 2714 strain exuded glycerol as the main carbon compound. In turn, A. brasilense exuded uracil when grown on the exudates of either microalga, and both microalga strains were able to utilize uracil as a nitrogen source. Interestingly, although the total carbohydrate content was higher in exudates from C. sorokiniana UTEX 2805 than from C. sorokiniana UTEX 2714, the growth of A. brasilense was greater in the exudates from the UTEX 2714 strain. These results highlight the fact that in the exuded carbon compounds differ between strains of the same species of microalgae and suggest that the type, rather than the quantity, of carbon source is more important for sustaining the growth of the partner bacteria.

Integrated Metabolomics and Morpho-Biochemical Analyses Reveal a Better Performance of Azospirillum brasilense over Plant-Derived Biostimulants in Counteracting Salt Stress in Tomato.

Increased soil salinity is one of the main concerns in agriculture and food production, and it negatively affects plant growth and crop productivity. In order to mitigate the adverse effects of salinity stress, plant biostimulants (PBs) have been indicated as a promising approach. Indeed, these products have a beneficial effect on plants by acting on primary and secondary metabolism and by inducing the accumulation of protective molecules against oxidative stress. In this context, the present work is aimed at comparatively investigating the effects of microbial (i.e., Azospirillum brasilense) and plant-derived biostimulants in alleviating salt stress in tomato plants by adopting a multidisciplinary approach. To do so, the morphological and biochemical effects were assessed by analyzing the biomass accumulation and root characteristics, the activity of antioxidant enzymes and osmotic stress protection. Furthermore, modifications in the metabolomic profiles of both leaves and root exudates were also investigated by ultra-high performance liquid chromatography/quadrupole time-of-flight mass spectrometry (UHPLC/QTOF-MS). According to the results, biomass accumulation decreased under high salinity. However, the treatment with A. brasilense considerably improved root architecture and increased root biomass by 156% and 118% in non-saline and saline conditions, respectively. The antioxidant enzymes and proline production were enhanced in salinity stress at different levels according to the biostimulant applied. Moreover, the metabolomic analyses pointed out a wide set of processes being affected by salinity and biostimulant interactions. Crucial compounds belonging to secondary metabolism (phenylpropanoids, alkaloids and other N-containing metabolites, and membrane lipids) and phytohormones (brassinosteroids, cytokinins and methylsalicylate) showed the most pronounced modulation. Overall, our results suggest a better performance of A. brasilense in alleviating high salinity than the vegetal-derived protein hydrolysates herein evaluated.

Chitosan/starch beads as bioinoculants carrier: long-term survival of bacteria and plant growth promotion.

Immobilization of microorganisms in biodegradable polymeric matrices constitutes a promising technology for plant growth promoting to overcome the challenging conditions of the rhizosphere. Previously, we demonstrated that beads prepared from blends of chitosan/starch of analytical grades ionically cross-linked are useful carriers for Azospirillum brasilense and Pseudomonas fluorescens. The aims of this work were to study A. brasilense Az39 and P. fluorescens ZME4 immobilization in industrial quality beads produced with a blend of chitosan/starch, to assess bacterial survival during long-term storage and biofilm distribution in the beads. We also proposed to analyze the consortia root colonization and its performance as plant growth-promoting bioinoculants compared to liquid counterpart. Our results revealed that A. brasilense Az39 and P. fluorescens ZME4 can coexist in industrial grade chitosan/starch beads, and this mixed immobilization benefits the survival rates of both species, even for more than a year under shelf storage. Confocal laser scanning microscopy with fluorescent dyed strains showed that both species remain mainly in different locations inside and over the beads. Additionally, maize seed treatment with beads-loaded bacteria resulted in growth promotion of roots in a similar manner than traditional liquid-based inoculation. The evidence collected here demonstrate that low-cost chitosan/starch beads are a suitable carrier for bacteria consortia and could be a reliable alternative to liquid inoculation in agronomic practices with additional benefits for industrial management. KEY POINTS: • Mixed immobilization increases bacterial survival in chitosan/starch industrial beads • Beads increase competence of bacteria in rhizosphere of maize • Inoculation mediated by beads promotes plant growth of maize.