Bacterial Inoculation Research Articles

Bacterial inoculation remediates heavy metals toxicity through modulating biochemicals and antioxidant enzymes of Daucus carota L. grown in lead contaminated soil

Due to streamlined industrialization, soil contamination has become major cause of scaling down of the crop productivity. In the course of current study, the negative effects of lead (Pb) contaminated soil on growth, physiology, antioxidative enzymes and yield of selected genotypes of carrot (Daucus carota L.) were studied. The conclusions drawn from the conducted research depicts that all growth contributing factors were divulges to be decreased under the influence of standardized treatment of lead (Pb). Pb toxicity also reduced yield contributing factors of carrots i.e. root length, diameter and weight. Bio-inoculants improved yield of carrots not only in control but also under Pb stressed conditions. Total soluble sugars and reducing sugars were also reduced by Pb toxicity; while bio-inoculants treatment tends to lower the negative effects of Pb toxicity. The level of enzymes phenylalanine ammonia lyase, polyphenol oxidase and peroxidase increased significantly in response to Pb toxicity. Bio-inoculants reduced the accumulation of these enzymes hence indicating amelioration of Pb toxicity. Application of bio-inoculants played a pivotal role to ameliorate lead (Pb) toxicity, thus, can be potentially used to eradicate Pb stress in contaminated sites. The selected 29 genotypes are categorized into three groups, highly tolerant, moderately tolerant and susceptible.

Impact of PGPR inoculation on root morphological traits and root exudation in rapeseed and camelina: interactions with heat stress.

Root exudation is involved in the recruitment of beneficial microorganisms by trophic relationships and/or signalling pathways. Among beneficial microorganisms, Plant Growth-Promoting Rhizobacteria (PGPR) are known to improve plant growth and stress resistance. These interactions are of particular importance for species that do not interact with mycorrhizal fungi, such as rapeseed (Brassica napus L.) and camelina (Camelina sativa (L.) Crantz). However, heat stress is known to have a quantitative and qualitative impact on root exudation and could affect the interactions between plants and PGPR. We aimed to analyse the effects of PGPR inoculation on root morphology and exudation in rapeseed and camelina at the reproductive stage. The modulation of the effects of these interactions under heat stress was also investigated. The plants were inoculated twice at the reproductive stage with two different Pseudomonas species and were exposed to heat stress after the second inoculation. In non-stressing conditions, after bacterial inoculation, rapeseed and camelina exhibited two contrasting behaviours in C root allocation. While rapeseed plants seemed to suffer from the interactions with the bacteria, camelina plants appeared to control the relationship with the PGPR by modifying the composition of their root exudates. Under heat stress, the plant-PGPR interaction was unbalanced for rapeseed, for which the C allocation strategy is mainly driven by the C cost from the bacteria. Alternatively, camelina plants prioritized C allocation for their own above-ground development. This work opens up new perspectives for understanding plant-PGPR interactions, especially in an abiotic stress context.

Plant growth promoting rhizobacteria induced metal and salt stress tolerance in Brassica juncea through ion homeostasis

Soil heavy metal contamination and salinity constitute a major environmental problem worldwide. The affected area and impact of these problems are increasing day by day; therefore, it is imperative to restore their potential using environmentally friendly technology. Plant growth-promoting rhizobacteria (PGPR) provides a better option in this context. Thirty-seven bacteria were isolated from the rhizosphere of maize cultivated in metal- and salt-affected soils. Some selected bacterial strains grew well under a wide range of pH (4−10), salt (5–50 g/L), and Cd (50–1000 mg/L) stress. Three bacterial strains, Exiguobacterium aestuarii (UM1), Bacillus cereus (UM8), and Bacillus megaterium (UM35), were selected because of their robust growth and high tolerance to both stress conditions. The bacterial strains UM1, UM8, and UM35 showed P-solubilization, whereas UM8 and UM35 exhibited 1-aminocyclopropane-1-carboxylate deaminase activity and indole acetic acid (IAA) production, respectively. The bacterial strains were inoculated on Brassica juncea plants cultivated in Cd and salt-affected soils due to the above PGP activities and stress tolerance. Plants inoculated with the bacterial strains B. cereus and B. megaterium significantly (p < 0.05) increased shoot fresh weight (17 ± 1.17–29 ± 0.88 g/plant), shoot dry weight (2.50 ± 0.03–4.40 ± 0.32 g/plant), root fresh weight (7.30 ± 0.58–13.30 ± 0.58 g/plant), root dry weight (0.80 ± 0.04–2.00 ± 0.01 g/plant), and shoot K contents (62.76 ± 1.80–105.40 ± 1.15 mg/kg dwt) in normal and stressful conditions. The bacterial strain B. megaterium significantly (p < 0.05) decreased shoot Na+ and Cd++ uptake in single and dual stress conditions. Both bacterial strains, E. aestuarii and B. cereus, efficiently reduced Cd++ translocation and bioaccumulation in the shoot. Bacterial inoculation improved the uptake of K+ and Ca++, while restricted Na+ and Cd++ in B. juncea shoots indicated their potential to mitigate the dual stresses of salt and Cd in B. juncea through ion homeostasis.

Transurethral Catheterization and Bacterial Inoculation to Generate a Urinary Tract Infection Model in Male Mice

Transurethral Catheterization and Bacterial Inoculation to Generate a Urinary Tract Infection Model in Male Mice

Mathematical modeling for operative improvement of the decoloration of Acid Red 27 by a novel microbial consortium of Trametes versicolor and Pseudomonas putida: A multivariate sensitivity analysis

In this work, it is presented a first approach of a mathematical and kinetic analysis for improving the decoloration and further degradation process of an azo dye named acid red 27 (AR27), by means of a novel microbial consortium formed by the fungus Trametes versicolor and the bacterium Pseudomonas putida. A multivariate analysis was carried out by simulating scenarios with different operating conditions and developing a specific mathematical model based on kinetic equations describing all stages of the biological process, from microbial growth and substrate consuming to decoloration and degradation of intermediate compounds. Additionally, a sensitivity analysis was performed by using a factorial design and the Response Surface Method (RSM), for determining individual and interactive effects of variables like, initial glucose concentration, initial dye concentration and the moment in time for bacterial inoculation, on response variables assessed in terms of the minimum time for: full decoloration of AR27 (R1 = 2.375 days); maximum production of aromatic metabolites (R2 = 1.575 days); and full depletion of aromatic metabolites (R3 = 12.9 days). Using RSM the following conditions improved the biological process, being: an initial glucose concentration of 20 g l-1, an initial AR27 concentration of 0.2 g l-1 and an inoculation moment in time of P. putida at day 1. The mathematical model is a feasible tool for describing AR27 decoloration and its further degradation by the microbial consortium of T. versicolor and P. putida, this model will also work as a mathematical basis for designing novel bio-reaction systems than can operate with the same principle of the described consortium.

Transurethral Catheterization and Bacterial Inoculation to Generate a Urinary Tract Infection Model in Male Mice

Transurethral Catheterization and Bacterial Inoculation to Generate a Urinary Tract Infection Model in Male Mice

Growth response of cowpea (Vigna unguiculata L.) exposed to Pseudomonas fluorescens, Pseudomonas stutzeri, and Pseudomonas gessardii in lead contaminated soil

Lead (Pb) is a major contaminant among heavy metals in the soil environment that has negative impacts on the growth of plants, which ultimately cause health risk via entering into the food chain. In this regard, plant growth promoting rhizobacteria (PGPR) might improve plant growth by counteracting the harmful effects of Pb stress. Therefore, the present pot study was conducted to evaluate the role of PGPR in improving the growth of cowpea in Pb-contaminated soil. Three different concentrations of Pb (250, 350, and 750 mg kg−1) were applied alone (control) and in combination with bacterial inoculums [S1 (Pseudomonas fluorescens), S2 (Pseudomonas stutzeri) and S3 (Pseudomonas gessardii)] using completely randomized design each with three replicates. Results showed that plant fresh weight, plant dry weight, shoot length, root length, and chlorophyll contents of cowpea plants were improved significantly (P ≤ 0.05) by applying bacterial isolates as compared to the un-inoculated contaminated control. Among bacterial isolates, S3 performed better as compared to other bacterial isolates. The maximum increase in plant fresh weight, plant dry weight, shoot length, root length, and chlorophyll content was observed under S3 bacterial strain. Bacterial inoculation also enhanced the Pb concentration in the plant and the maximum uptake was recorded under S3 bacterial strain at 750 mg kg−1. Consequently, it has been concluded that PGPR has the great potential to enhance the plant growth and physiological characteristics of cowpea in Pb-contaminated sites and can also be used for bioremediation purposes.

Screening of high-efficiency nitrogen-fixing bacteria from the traditional Chinese medicine plant Astragalus mongolicus and its effect on plant growth promotion and bacterial communities in the rhizosphere

BackgroundAstragalus mongolicus Bunge is used in traditional Chinese medicine and is thus cultivated in bulk. The cultivation of A. mongolicus requires a large amount of nitrogen fertilizer, increasing the planting cost of medicinal materials and polluting the environment. Isolation and screening of plant growth-promoting rhizobacteria (PGPR) and exploring the nitrogen fixation potential of A. mongolicus rhizosphere microorganisms would effectively reduce the production cost of A. mongolicus.ResultsThis study used A. mongolicus roots and rhizosphere soil samples from Longxi County of Gansu Province, Jingle County, and Hunyuan County of Shanxi Province, China, to isolate and identify nitrogen-fixing bacteria. Through nitrogen fixation efficiency test, single strain inoculation test, and plant growth-promoting characteristics, three strains, Bacillus sp. J1, Arthrobacter sp. J2, and Bacillus sp. G4 were selected from 86 strains of potential nitrogen-fixing bacteria, which were the most effective in promoting the A. mongolicus growth and increasing the nitrogen, phosphorus, and potassium content in plants. The antagonistic test showed that these bacteria could grow smoothly under the co-culture conditions. The J1, J2, and G4 strains were used in a mixed inoculum and found to enhance the biomass of A. mongolicus plants and the accumulation of the main medicinal components in the field experiment. Mixed bacterial agent inoculation also increased bacterial diversity and changed the structure of the bacterial community in rhizosphere soil. Meanwhile, the relative abundance of Proteobacteria increased significantly after inoculation, suggesting that Proteobacteria play an important role in plant growth promotion.ConclusionsThese findings indicate that specific and efficient PGPRs have a significant promoting effect on the growth of A. mongolicus, while also having a positive impact on the structure of the host rhizosphere bacteria community. This study provides a basis for developing a nitrogen-fixing bacterial fertilizer and improving the ecological planting efficiency of A. mongolicus.

Bacillus megaterium RTS1 enhances resistance of Lycopersicon esculentum to salinity stress through the improvement of antioxidant defenses

Background and Objectives: Plant growth-promoting bacteria (PGPB) may reduce the negative effects of salinity stress. The aim of this study was to optimize Bacillus megaterium RTS1 and characterize the effect of the PGPB on the physiolog- ical characteristics of tomato (Lycopersicon esculentum).&#x0D; Materials and Methods: The Central composite design (CCD) of response surface methodology (RSM) was used to opti- mize Bacillus megaterium RTS1 to produce maximum cell biomass and spores. Then the effect of the PGPB on the physi- ological characteristics of tomato (Lycopersicon esculentum), including membrane stability, leaf relative water content per- centage, anthocyanin and carotenoids content, chlorophyll photosynthetic parameters, sugar and starch level, superoxide anion and antioxidant activity under salt stress conditions. The NFB medium was inoculated with 5% bacterial culture and the fermentation was carried out in a 10-lit fermenter.&#x0D; Results: After optimization, the amount of cell biomass by the model was 9.45 log10 CFUs/mL, which showed a 1.2-fold increase compared to the non-optimized medium. Usage of bacteria under the optimal conditions of the culture medium may increase the stability of the membrane and improve the relative water content. Bacteria were able to prevent the excessive increase of anthocyanins. Oxidative stress led to an increase in the content of chlorophyll a, while causing the degradation of chlorophyll b. Bacterial inoculation led to an increase in the level of sugar and starch compared to the control. PGPB showed an increasing effect on the amount of superoxide anion production and caused a significant increase in the antioxidant activity under salinity stress conditions.&#x0D; Conclusion: The PGPB can be a promising way to boost physiological characteristics of tomato plant under salinity stress. Also, sporulation capacity of Bacillus megaterium with high bacterial cell density in fermenter produce a sustainable product for tomato plants.

Halotolerant endophytic bacteria alleviate salinity stress in rice (oryza sativa L.) by modulating ion content, endogenous hormones, the antioxidant system and gene expression

Excessive salinity reduces crop production and negatively impacts agriculture worldwide. We previously isolated endophytic bacterial strains from two halophytic species: Artemisia princeps and Chenopodium ficifolium. We used three bacterial isolates: ART-1 (Lysinibacillus fusiformis), ART-10 (Lysinibacillus sphaericus), and CAL-8 (Brevibacterium pityocampae) to alleviate the impact of salinity stress on rice. The impact of 160 mM NaCl salinity on rice was significantly mitigated following inoculation with these bacterial strains, resulting in increased growth and chlorophyll content. Furthermore, OsNHX1, OsAPX1, OsPIN1 and OsCATA expression was increased, but OsSOS expression was decreased. Inductively coupled plasma mass spectrometry (ICP-MS) revealed reduced K+ and Na+ levels in shoots of bacteria-inoculated plants, whereas that of Mg2+ was increased. Bacterial inoculation reduced the content of total flavonoids in rice leaves. Salinized plants inoculated with bacteria showed reduced levels of endogenous salicylic acid (SA) and abscisic acid (ABA) but increased levels of jasmonic acid (JA). In conclusion, the bacterial isolates ART-1, ART-10, and CAL-8 alleviated the adverse effect of salinity on rice growth, which justifies their use as an eco-friendly agricultural practice.

Effects of commercial bacterial inoculants on fermentation and nutritive quality of wheat and annual legume mixed silages

Effects of commercial bacterial inoculants on fermentation and nutritive quality of wheat and annual legume mixed silages

Effect of rhizospheric bacteria on growth, physiological attributes and melatonin contents of Trigonella foenum-graecum L.

Chemical fertilizers are economically important but environmentally these are unfit for the living organisms. Therefore, to solve this problem rhizobacteria were used as a substituent. The aim of this research was to investigate the effect of rhizospheric bacteria on growth, physiological attributes and endogenous melatonin contents of fenugreek (Trigonella foenum-graecum L.) varieties. Inorganic fertilizers (Urea and DAP) were used in experiment for comparison with bio-fertilizers (Bradyrhizobium joponicum and Burkholderia cepacia). It was found that plants under treatment of bacteria and fertilizers have more growth in comparison to control plants. Significant changes were observed in growth of plants. Rhizospheric bacterial amendments significantly improved endogenous melatonin level in all studied fenugreek varieties. Plants under bacterial treatments have represented positive changes in all the parameters which were studied as compare to control plants. From these results it is found that bacterial inoculants have beneficial effects on four varieties of fenugreek. These results suggested that beneficial bacteria can be essential and significant in reducing risks to ecosystems around the world.

Plant resistance to tomato yellow leaf curl virus is enhanced by Bacillus amyloliquefaciens Ba13 through modulation of RNA interference.

Tomato yellow leaf curl virus (TYLCV), which is a typical member of the genus Begomovirus, causes severe crop yield losses worldwide. RNA interference (RNAi) is an important antiviral defense mechanism in plants, but whether plant beneficial microbes used as biocontrol agents would modulate RNAi in defense against TYLCV remains unclear. Here, we employed whole-transcriptome, bisulfite, and small RNA sequencing to decipher the possible role of Bacillus amyloliquefaciens Ba13 as a bacterial biocontrol agent against TYLCV in RNAi modulation. Potted tomato plants were exposed to whiteflies for natural viral infection 14 days after bacterial inoculation. Compared with non-inoculated controls, the abundance of TYLCV gene in the leaves of inoculated plants decreased by 70.1% at 28 days post-infection, which mirrored the pattern observed for plant disease index. The expression of the ARGONAUTE family genes (e.g., AGO3, AGO4, AGO5, and AGO7) involved in antiviral defense markedly increased by 2.44-6.73-fold following bacterial inoculation. The methylation level at CpG site 228 (in the open reading frame region of the RNA interference suppressing gene AV2) and site 461 (in the open reading frame regions of AV1 and AV2) was 183.1 and 63.0% higher in inoculated plants than in non-inoculated controls, respectively. The abundances of 10 small interfering RNAs matched to the TYLCV genome were all reduced in inoculated plants, accompanied by enhancement of photosystem and auxin response pathways. The results indicate that the application of Ba. amyloliquefaciens Ba13 enhances plant resistance to TYLCV through RNAi modulation by upregulating RNAi-related gene expression and enhancing viral genome methylation.

Molecular and evolutionary basis of O-antigenic polysaccharide-driven phage sensitivity in environmental pseudomonads.

Pseudomonas protegens CHA0, a bacterial strain able to suppress plant pathogens as well as efficiently kill lepidopteran pest insects, has been studied as a biocontrol agent to prevent ensuing agricultural damage. However, the success of this method is dependent on efficient plant colonization by the bacterial inoculant, while it faces competition from the resident microbiota as well as predators such as bacteriophages. One of these naturally occurring phages, ΦGP100, was found to drastically reduce the abundance of CHA0 once inoculated into plant microcosms, resulting in the loss of plant protection effect against a phytopathogen. Here, we investigated the molecular determinants implicated in the interaction between CHA0 and the phage ΦGP100 using a high-density transposon-sequencing approach. We show that lipopolysaccharide cell surface decorations, specifically the longer OBC3-type O-antigenic polysaccharide (O-PS, O-antigen) of the two dominant O-PS of CHA0, are essential for the attachment and infection of ΦGP100. Moreover, when exploring the distribution of the OBC3 cluster in bacterial genomes, we identified several parts of this gene cluster that are conserved in phylogenetically distant bacteria. Through heterologous complementation, we integrated an OBC3-type gene copy from a phylogenetically distant bacterium and were able to restore the phage sensitivity of a CHA0 mutant which lacked the ability to form long O-PS. Finally, we evidence that the OBC3 gene cluster of CHA0 displays a high genomic plasticity and likely underwent several horizontal acquisitions and genomic rearrangements. Collectively, this study underlines the complexity of phage-bacteria interactions and the multifunctional aspect of bacterial cell surface decorations. IMPORTANCE The application of plant-beneficial microorganisms to protect crop plants is a promising alternative to the usage of chemicals. However, biocontrol research often faces difficulties in implementing this approach due to the inconsistency of the bacterial inoculant to establish itself within the root microbiome. Beneficial bacterial inoculants can be decimated by the presence of their natural predators, notably bacteriophages (also called phages). Thus, it is important to gain knowledge regarding the mechanisms behind phage-bacteria interactions to overcome this challenge. Here, we evidence that the major long O-antigenic polysaccharide (O-PS, O-antigen) of the widely used model plant-beneficial bacterium Pseudomonas protegens CHA0 is the receptor of its natural predator, the phage ΦGP100. We examined the distribution of the gene cluster directing the synthesis of this O-PS and identified signatures of horizontal gene acquisitions. Altogether, our study highlights the importance of bacterial cell surface structure variation in the complex interplay between phages and their Pseudomonas hosts.

Short-term heat stress assays resolve effects of host strain, repeat stress, and bacterial inoculation on Aiptasia thermal tolerance phenotypes

The ongoing loss of corals and their reef ecosystems hastens the need to develop approaches that mitigate the impacts of climate change. Given the strong reliance of corals on their associated prokaryotic and microalgal symbionts, microbiome-targeted interventions in the form of probiotics or microbiome transplants are emerging as potential solutions. Although inoculation with beneficial microorganisms was shown to improve coral bleaching recovery, the mechanistic underpinnings and extent to which microbiomes can be manipulated are largely unknown. Research progress in this regard is often hindered by coral holobiont complexity and a lack of standardized diagnostics to assess physiological and phenotypic changes following microbial manipulation. Here we address these shortcomings by establishing short-term acute thermal stress assays using the Coral Bleaching Automated Stress System (CBASS) as a standardized and reproducible experimental platform to assess stress tolerance phenotypes of the coral model Aiptasia. We show that thermal tolerance phenotypes following acute heat stress assays are highly reproducible, host species-specific, and can exert legacy effects with consequences for long-term thermal resilience. We further demonstrate the ability to resolve phenotypic differences in thermal tolerance following incubation with the coral bleaching pathogen Vibrio coralliilyticus, providing an avenue for screening bacteria for their ability to affect holobiont thermal performance. By employing acute heat stress assays in conjunction with a tractable model organism, we posit CBASS assays as a standardized experimental platform that allows functional screening for microbes that affect thermal stress tolerance. Such effort may accelerate the discovery of microbes and microbial mechanisms mediating thermal tolerance and our ability to harness them to increase stress resilience.

Hordeum vulgare differentiates its response to beneficial bacteria

BackgroundIn nature, beneficial bacteria triggering induced systemic resistance (ISR) may protect plants from potential diseases, reducing yield losses caused by diverse pathogens. However, little is known about how the host plant initially responds to different beneficial bacteria. To reveal the impact of different bacteria on barley (Hordeum vulgare), bacterial colonization patterns, gene expression, and composition of seed endophytes were explored.ResultsThis study used the soil-borne Ensifer meliloti, as well as Pantoea sp. and Pseudomonas sp. isolated from barley seeds, individually. The results demonstrated that those bacteria persisted in the rhizosphere but with different colonization patterns. Although root-leaf translocation was not observed, all three bacteria induced systemic resistance (ISR) against foliar fungal pathogens. Transcriptome analysis revealed that ion- and stress-related genes were regulated in plants that first encountered bacteria. Iron homeostasis and heat stress responses were involved in the response to E. meliloti and Pantoea sp., even if the iron content was not altered. Heat shock protein-encoding genes responded to inoculation with Pantoea sp. and Pseudomonas sp. Furthermore, bacterial inoculation affected the composition of seed endophytes. Investigation of the following generation indicated that the enhanced resistance was not heritable.ConclusionsHere, using barley as a model, we highlighted different responses to three different beneficial bacteria as well as the influence of soil-borne Ensifer meliloti on the seed microbiome. In total, these results can help to understand the interaction between ISR-triggering bacteria and a crop plant, which is essential for the application of biological agents in sustainable agriculture.

Establishment of persistent enteric mycobacterial infection following streptomycin pre-treatment

Mycobacterium avium subsp. paratuberculosis (MAP) is the causative agent of paratuberculosis, a chronic gastrointestinal disease affecting ruminants. This disease remains widespread in part due to the limitations of available diagnostics and vaccines. A representative small animal model of disease could act as a valuable tool for studying its pathogenesis and to develop new methods for paratuberculosis control, but current models are lacking. Streptomycin pre-treatment can reduce colonization resistance and has previously been shown to improve enteric infection in a Salmonella model. Here, we investigated whether streptomycin pre-treatment of mice followed by MAP gavage could act as a model of paratuberculosis which mimics the natural route of infection and disease development in ruminants. The infection outcomes of MAP were compared to M. avium subsp. hominissuis (MAH), an environmental mycobacterium, and M. bovis and M. orygis, two tuberculous mycobacteria. Streptomycin pre-treatment was shown to consistently improve bacterial infection post-oral inoculation. This model led to chronic MAP infection of the intestines and mesenteric lymph nodes (MLNs) up to 24-weeks post-gavage, however there was no evidence of inflammation or disease. These infection outcomes were found to be specific to MAP. When the model was applied to a bacterium of lesser virulence MAH, the infection was comparatively transient. Mice infected with bacteria of greater virulence, M. bovis or M. orygis, developed chronic intestinal and MLN infection with pulmonary disease similar to zoonotic TB. Our findings suggest that a streptomycin pre-treatment mouse model could be applied to future studies to improve enteric infection with MAP and to investigate other modifications underlying MAP enteritis.

Application Effects of Bacterial Inoculants Producing Chitinase on Corn Silage

Application Effects of Bacterial Inoculants Producing Chitinase on Corn Silage

Changes in structure and assembly of a species-rich soil natural community with contrasting nutrient availability upon establishment of a plant-beneficial Pseudomonas in the wheat rhizosphere

BackgroundPlant-beneficial bacterial inoculants are of great interest in agriculture as they have the potential to promote plant growth and health. However, the inoculation of the rhizosphere microbiome often results in a suboptimal or transient colonization, which is due to a variety of factors that influence the fate of the inoculant. To better understand the fate of plant-beneficial inoculants in complex rhizosphere microbiomes, composed by hundreds of genotypes and multifactorial selection mechanisms, controlled studies with high-complexity soil microbiomes are needed.ResultsWe analysed early compositional changes in a taxa-rich natural soil bacterial community under both exponential nutrient-rich and stationary nutrient-limited growth conditions (i.e. growing and stable communities, respectively) following inoculation with the plant-beneficial bacterium Pseudomonas protegens in a bulk soil or a wheat rhizosphere environment. P. protegens successfully established under all conditions tested and was more abundant in the rhizosphere of the stable community. Nutrient availability was a major factor driving microbiome composition and structure as well as the underlying assembly processes. While access to nutrients resulted in communities assembled mainly by homogeneous selection, stochastic processes dominated under the nutrient-deprived conditions. We also observed an increased rhizosphere selection effect under nutrient-limited conditions, resulting in a higher number of amplicon sequence variants (ASVs) whose relative abundance was enriched. The inoculation with P. protegens produced discrete changes, some of which involved other Pseudomonas. Direct competition between Pseudomonas strains partially failed to replicate the observed differences in the microbiome and pointed to a more complex interaction network.ConclusionsThe results of this study show that nutrient availability is a major driving force of microbiome composition, structure and diversity in both the bulk soil and the wheat rhizosphere and determines the assembly processes that govern early microbiome development. The successful establishment of the inoculant was facilitated by the wheat rhizosphere and produced discrete changes among other members of the microbiome. Direct competition between Pseudomonas strains only partially explained the microbiome changes, indicating that indirect interactions or spatial distribution in the rhizosphere or soil interface may be crucial for the survival of certain bacteria.B5pQk-pebCjYS-vjJfR65XVideo

Effect of Different Plant Growth-Promoting Rhizobacteria on Biological Soil Properties, Growth, Yield and Quality of Oregano (Origanum onites L.)

Intensive agriculture uses continuous chemical fertilizers to increase crop yields, but excessive use of fertilizers leads to environmental pollution, permanent changes in physicochemical conditions in soil ecology, deterioration of soil biological health, leaching of nutrients, surface and groundwater pollution and eutrophication. Plant growth-promoting rhizobacteria (PGPR) are becoming increasingly important for ensuring crop safety, increasing nutrient uptake and output, lowering fertilizer costs, preventing environmental contamination and promoting sustainable agriculture and agricultural resources. Therefore, the purpose of this study was to identify and evaluate the effects of fifteen bacteria strains that were isolated from various acidic rhizospheric soils as biofertilizers on soil biological properties. Growth, yield and quality traits were analyzed, and various PGPR were identified using 16S ribosomal RNA of Turkish oregano. Fifteen bacterial inoculations with 1-aminocyclopropane-1-carboxylate (ACC) deaminase, N2-fixing, P-solubilizing and/or IAA-producing genes were used in the experiment, which was carried out in a randomized block design with five replicates (each with three pots) and a control without inoculation. Increased biological activity in soil inoculated with bacteria with multiple traits was confirmed by high C and N content in microbial biomass, urease, dehydrogenase and acid and alkaline phosphatase activities. Essential oil content, oil yield, thymol and carvacrol contents increased by 0.5–40.1%, 5.9–71.9%, 0.07–16.7% and 0.3–9.2%, respectively, as a result of bacterial inoculation. Oil content ranged from 2.02% to 2.83%; carvacrol (66.1–72.2%) was the main constituent, followed by thymol (14.5–16.9%) and linalool (1.38–3.68%). Two large PGPR groups were formed based on genetic distance analysis. Responses were variable and depended on the inoculant strain and the parameters being evaluated. The results indicate PGPR has clear potential for improving the yield of cultivated aromatic and essential oil plants, such as oregano.