Improving Lead Phytoremediation Using Endophytic Bacteria Isolated from the Pioneer Plant Ageratina adenophora (Spreng.) from a Mining Area.

This study aimed to isolate and characterise endophytic bacteria from the pioneer plant Ageratina adenophora in a mining area. Seven strains of metal-resistant endophytic bacteria that belong to five genera were isolated from the roots of A. adenophora. These strains exhibited various plant growth-promoting (PGP) capabilities. Sphingomonas sp. ZYG-4, which exhibited the ability to secrete indoleacetic acid (IAA; 53.2 ± 8.3 mg·L-1), solubilize insoluble inorganic phosphates (Phosphate solubilization; 11.2 ± 2.9 mg·L-1), and regulate root ethylene levels (1-aminocyclopropane-1-carboxylic acid deaminase activity; 2.87 ± 0.19 µM α-KB·mg-1·h-1), had the highest PGP potential. Therefore, Sphingomonas sp. ZYG-4 was used in a pot experiment to study its effect on the biomass and Pb uptake of both host (Ageratina adenophora) and non-host (Dysphania ambrosioides) plants. Compared to the uninoculated control, Sphingomonas sp. ZYG-4 inoculation increased the biomass of shoots and roots by 59.4% and 144.4% for A. adenophora and by 56.2% and 57.1% for D. ambrosioides, respectively. In addition, Sphingomonas sp. ZYG-4 inoculation enhanced Pb accumulation in the shoot and root by 268.9% and 1187.3% for A. adenophora, and by 163.1% and 343.8% for D. ambrosioides, respectively, compared to plants without bacterial inoculation. Our research indicates that endophytic bacteria are promising candidates for enhancing plant growth and facilitating microbe-assisted phytoremediation in heavy metal-contaminated soil.

Effects of Klebsiella michiganensis LDS17 on Codonopsis pilosula growth, rhizosphere soil enzyme activities, and microflora, and genome-wide analysis of plant growth-promoting genes.

Codonopsis pilosula is a perennial herbaceous liana with medicinal value. It is critical to promote Codonopsis pilosula growth through effective and sustainable methods, and the use of plant growth-promoting bacteria (PGPB) is a promising candidate. In this study, we isolated a PGPB, Klebsiella michiganensis LDS17, that produced a highly active 1-aminocyclopropane-1-carboxylate deaminase from the Codonopsis pilosula rhizosphere. The strain exhibited multiple plant growth-promoting properties. The antagonistic activity of strain LDS17 against eight phytopathogenic fungi was investigated, and the results showed that strain LDS17 had obvious antagonistic effects on Rhizoctonia solani, Colletotrichum camelliae, Cytospora chrysosperma, and Phomopsis macrospore with growth inhibition rates of 54.22%, 49.41%, 48.89%, and 41.11%, respectively. Inoculation of strain LDS17 not only significantly increased the growth of Codonopsis pilosula seedlings but also increased the invertase and urease activities, the number of culturable bacteria, actinomycetes, and fungi, as well as the functional diversity of microbial communities in the rhizosphere soil of the seedlings. Heavy metal (HM) resistance tests showed that LDS17 is resistant to copper, zinc, and nickel. Whole-genome analysis of strain LDS17 revealed the genes involved in IAA production, siderophore synthesis, nitrogen fixation, P solubilization, and HM resistance. We further identified a gene (koyR) encoding a plant-responsive LuxR solo in the LDS17 genome. Klebsiella michiganensis LDS17 may therefore be useful in microbial fertilizers for Codonopsis pilosula. The identification of genes related to plant growth and HM resistance provides an important foundation for future analyses of the molecular mechanisms underlying the plant growth promotion and HM resistance of LDS17. IMPORTANCE: We comprehensively evaluated the plant growth-promoting characteristics and heavy metal (HM) resistance ability of the LDS17 strain, as well as the effects of strain LDS17 inoculation on the Codonopsis pilosula seedling growth and the soil qualities in the Codonopsis pilosula rhizosphere. We conducted whole-genome analysis and identified lots of genes and gene clusters contributing to plant-beneficial functions and HM resistance, which is critical for further elucidating the plant growth-promoting mechanism of strain LDS17 and expanding its application in the development of plant growth-promoting agents used in the environment under HM stress.

Co-inoculation of the endophytes Bacillus thuringiensis CAPE95 and Paenibacillus polymyxa CAPE238 promotes Tropaeolum majus L. growth and enhances its root bacterial diversity.

Tropaeolum majus L. is a versatile edible plant that is widely explored due to its medicinal properties and as a key element in intercropping systems. Its growth could be improved by the use of biofertilizers that can enhance nutrient uptake by the plant or provide tolerance to different abiotic and biotic stresses. In a previous study, 101 endophytes isolated from T. majus roots showed more than three plant growth-promoting (PGP) features in vitro, such as phosphate mineralization/solubilization, production of siderophores, antimicrobial substances and indole-related compounds, and presence of the nifH gene. To provide sustainable alternatives for biofertilization, the genomes of two promising endophytes-CAPE95 and CAPE238-were sequenced to uncover metabolic pathways related to biofertilization. Greenhouse experiments were conducted with 216 seeds and 60 seedlings, half co-inoculated with the endophytes (treatment) and half inoculated with 1X PBS (control), and the impact of the co-inoculation on the plant's bacteriome was accessed through 16S rRNA gene metabarcoding. The strains CAPE95 and CAPE238 were taxonomically assigned as Bacillus thuringiensis and Paenibacillus polymyxa, respectively. Metabolic pathways related to the enhancement of nutrient availability (nitrogen fixation, sulfate-sulfur assimilation), biosynthesis of phytohormones (indole-3-acetic acid precursors) and antimicrobial substances (bacilysin, paenibacillin) were found in their genomes. The in vivo experiments showed that treated seeds exhibited faster germination, with a 20.3% higher germination index than the control on the eleventh day of the experiment. Additionally, treated seedlings showed significantly higher plant height and leaf diameters (p < 0.05). The bacterial community of the treated plants was significantly different from that of the control plants (p < 0.001) and showed a higher richness and diversity of species (Chao and Shannon indexes, p < 0.001). A higher relative abundance of potential synergistic PGP bacteria was also shown in the bacteriome of the treated plants, such as Lysinibacillus and Geobacter. For the first time, co-inoculation of B. thuringiensis and P. polymyxa was shown to have great potential for application as a biofertilizer to T. majus plants. The bacterial consortium used here could also be explored in other plant species in the future.

Integrated omics approach reveals the molecular pathways activated in tomato by Kocuria rhizophila, a soil plant growth-promoting bacterium.

Plant microbial biostimulants application has become a promising and eco-friendly agricultural strategy to improve crop yields, reducing chemical inputs for more sustainable cropping systems. The soil dwelling bacterium Kocuria rhizophila was previously characterized as Plant Growth Promoting Bacteria (PGPB) for its multiple PGP traits, such as indole-3-acetic acid production, phosphate solubilization capability and salt and drought stress tolerance. Here, we evaluated by a multi-omics approach, the PGP activity of K. rhizophila on tomato, revealing the molecular pathways by which it promotes plant growth. Transcriptomic analysis showed several up-regulated genes mainly related to amino acid metabolism, cell wall organization, lipid and secondary metabolism, together with a modulation in the DNA methylation profile, after PGPB inoculation. In agreement, proteins involved in photosynthesis, cell division, and plant growth were highly accumulated by K. rhizophila. Furthermore, "amino acid and peptides", "monosaccharides", and "TCA" classes of metabolites resulted the most affected by PGPB treatment, as well as dopamine, a catecholamine neurotransmitter mediating plant growth through S-adenosylmethionine decarboxylase (SAMDC), a gene enhancing the vegetative growth, up-regulated in tomato by K. rhizophila treatment. Interestingly, eight gene modules well correlated with differentially accumulated proteins (DAPs) and metabolites (DAMs), among which two modules showed the highest correlation with nine proteins, including a nucleoside diphosphate kinase, and cytosolic ascorbate peroxidase, as well as with several amino acids and metabolites involved in TCA cycle. Overall, our findings highlighted that sugars and amino acids, energy regulators, involved in tomato plant growth, were strongly modulated by the K. rhizophila-plant interaction.

Unveiling stress-adapted endophytic bacteria: Characterizing plant growth-promoting traits and assessing cross-inoculation effects on Populus deltoides under abiotic stress.

In the face of the formidable environmental challenges precipitated by the ongoing climate change, Plant Growth-Promoting Bacteria (PGPB) are gaining widespread acknowledgement for their potential as biofertilizers, biocontrol agents, and microbial inoculants. However, a knowledge gap pertains to the ability of PGPB to improve stress tolerance in forestry species via cross-inoculation. To address this gap, the current investigation centres on PGPBs, namely, Acinetobacter johnsonii, Cronobacter muytjensii, and Priestia endophytica, selected from the phyllosphere of robust and healthy plants thriving in the face of stress-inducing conditions. These strains were selected based on their demonstrated adaptability to saline, arid, and nitrogen-deficient environments. The utilization of PGPB treatment resulted in an improvement of stomatal conductance (gs) and transpiration rate (E) in poplar plants exposed to both salt and drought stress. It also induced an increase in essential biochemical components such as proline (PRO), catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD). These reactions were accompanied by a decrease in leaf malonaldehyde (MDA) content and electrolyte leakage (EL). Furthermore, the PGPB treatment demonstrated a notable enhancement in nutrient absorption, particularly nitrogen and carbon, achieved through the solubilization of nutrients. The estimation of canopy temperature via thermal imaging proved to be an efficient method for distinguishing stress reactions in poplar than conventional temperature recording techniques. In summation, the utilization of PGPB especially Cronobacter muytjensii in this study, yielded profound improvements in the stress tolerance of poplar plants, manifesting in reduced membrane lipid peroxidation, enhanced photosynthesis, and bolstered antioxidant capacity within the leaves.

Cold-adapted Exiguobacterium sibiricum K1 as a potential bioinoculant in cold regions: Physiological and genomic elucidation of biocontrol and plant growth promotion.

The scarcity of soil nutrient availability under cold conditions of Himalayan regions needs a sustainable approach for better crop yields. The cold-adapted bacteria, Exiguobacterium sibiricum K1, with the potential to produce several plant growth-promoting (PGP) attributes, nitrogen fixation, indole acetic acid production, phosphate and potassium solubilization at 10 °C can provide an opportunity to promote crop yield improvement in an eco-friendly way under cold conditions. The bacterium also exhibited biocontrol activity against two phytopathogens and produced siderophore (53.0 ± 0.5 % psu). The strain's PGP properties were investigated using a spinach-based bioassay under controlled conditions. The bacterized seeds showed a notable increase in germination rate (23.2 %), shoot length (65.3 %), root length (56.6 %), leaf area (73.7 %), number of leaflets (65.2 %), and dry matter (65.2 %). Additionally, the leaf analysis indicated elevated chlorophyll pigments, i.e., chlorophyll a (55.5 %), chlorophyll b (42.8 %), carotenoids (35.2 %), percentage radical scavenging activity (47.4 %), and leaf nutrient uptake such as nitrogen (23.4 %), calcium (60.8 %), potassium (62.3 %), and magnesium (28.9 %). Moreover, the whole-genome sequencing and genome mining endorsed various biofertilisation-related genes, including genes for potassium and phosphate solubilization, iron and nitrogen acquisition, carbon dioxide fixation, and biocontrol ability of Exiguobacterium sibiricum K1. Overall, this study highlights the role of Exiguobacterium sibiricum K1 as a potential bioinoculant for improving crop yield under cold environments.

Simultaneous Impact of Rhizobacteria Inoculation and Leaf-Chewing Insect Herbivory on Essential Oil Production and VOC Emissions in Ocimum basilicum.

Inoculation with rhizobacteria and feeding by herbivores, two types of abiotic stress, have been shown to increase the production of secondary metabolites in plants as part of the defense response. This study explored the simultaneous effects of inoculation with Bacillus amyloliquefaciens GB03 (a PGPR species) and herbivory by third-instar Spodoptera frugiperda larvae on essential oil (EO) yield and volatile organic compound (VOC) emissions in Ocimum basilicum plants. The density of glandular trichomes was also examined, given that they are linked to EO production and VOC emission. Herbivory increased EO content, but inoculation on its own did not. When combined, however, the two treatments led to a 10-fold rise in EO content with respect to non-inoculated plants. VOC emissions did not significantly differ between inoculated and non-inoculated plants, but they doubled in plants chewed by the larvae with respect to their undamaged counterparts. Interestingly, no changes were observed in VOC emissions when the treatments were tested together. In short, the two biotic stressors elicited differing plant defense responses, mainly when EO was concerned. PGPR did not stimulate EO production, while herbivory significantly enhanced it and increased VOC emissions. The combined treatment acted synergistically, and in this case, PGPR inoculation may have had a priming effect that amplified plant response to herbivory. Peltate trichome density was higher in inoculated plants, those damaged by larvae, and those subjected to the combination of both treatments. The findings highlight the intricate nature of plant defense mechanisms against various stressors and hint at a potential strategy to produce essential oil through the combined application of the two stressors tested here.

Assisted phytoextraction as a nature-based solution for the sustainable remediation of metal(loid)-contaminated soils.

Soil contamination is a significant environmental issue that poses a threat to human health and the ecosystems. Conventional remediation techniques, such as excavation and landfilling, are often expensive, disruptive, and unsustainable. As a result, there has been growing interest in developing sustainable remediation strategies that are cost-effective, environmentally friendly, and socially acceptable. One such solution is phytoextraction: a nature-based approach that uses the abilities of hyperaccumulator plants to uptake and accumulate metals and metalloids (potentially toxic elements [PTE]) without signs of toxicity. Once harvested, plant biomass can be treated to reduce its volume and weight by combustion, thus obtaining bioenergy, and the ashes can be used for the recovery of metals or in the construction industry. However, phytoextraction has shown variable effectiveness due to soil conditions and plant species specificity, which has led researchers to develop additional approaches known as assisted phytoextraction to enhance its success. Assisted phytoextraction is a remediation strategy based on modifying certain plant traits or using different materials to increase metal uptake or bioavailability. This review article provides a practical and up-to-date overview of established strategies and the latest scientific advancements in assisted phytoextraction. Our focus is on improving plant performance and optimizing the uptake, tolerance, and accumulation of PTE, as well as the accessibility of these contaminants. While we highlight the advantages of using hyperaccumulator plants for assisted phytoextraction, we also address the challenges and limitations associated with this approach. Factors such as soil pH, nutrient availability, and the presence of other contaminants can affect its efficiency. Furthermore, the real-world challenges of implementing phytoextraction on a large scale are discussed and strategies to modify plant traits for successful phytoremediation are presented. By exploring established strategies and the latest scientific developments in assisted phytoextraction, this review provides valuable guidance for optimizing a sustainable, nature-based technology. Integr Environ Assess Manag 2024;00:1-20. © 2024 SETAC.

Effects of plant growth-promoting rhizobacteria on blueberry growth and rhizosphere soil microenvironment.

Background: Plant growth-promoting rhizobacteria (PGPR) have a specific symbiotic relationship with plants and rhizosphere soil. The purpose of this study was to evaluate the effects of PGPR on blueberry plant growth, rhizospheric soil nutrients and the microbial community. Methods: In this study, nine PGPR strains, belonging to the genera Pseudomonas and Buttiauxella, were selected and added into the soil in which the blueberry cuttings were planted. All the physiological indexes of the cuttings and all rhizospheric soil element contents were determined on day 6 after the quartic root irrigation experiments were completed. The microbial diversity in the soil was determined using high-throughput amplicon sequencing technology. The correlations between phosphorus solubilization, the auxin production of PGPR strains, and the physiological indexes of blueberry plants, and the correlation between rhizospheric microbial diversity and soil element contents were determined using the Pearson's correlation, Kendall's tau correlation and Spearman's rank correlation analysis methods. Results: The branch number, leaf number, chlorophyllcontentand plant height of the treated blueberry group were significantly higher than those of the control group. The rhizospheric soil element contents also increased after PGPR root irrigation. The rhizospheric microbial community structure changed significantly under the PGPR of root irrigation. The dominant phyla, except Actinomycetota, in the soil samples had the greatest correlation with phosphorus solubilization and the auxin production of PGPR strains. The branch number, leaf number, and chlorophyllcontent had a positive correlation with the phosphorus solubilization and auxin production of PGPR strains and soil element contents. In conclusion, plant growth could be promoted by the root irrigation of PGPR to improve rhizospheric soil nutrients and the microenvironment, with modification of the rhizospheric soil microbial community. Discussion: Plant growth could be promoted by the root irrigation of PGPR to improve rhizospheric soil nutrients and the microenvironment, with the modification of the rhizospheric soil microbial community. These data may help us to better understand the positive effects of PGPR on blueberry growth and the rhizosphere soil microenvironment, as well as provide a research basis for the subsequent development of a rhizosphere-promoting microbial fertilizer.

Exploring the Trends in Actinobacteria as Biological Control Agents of Phytopathogenic Fungi: A (Mini)-Review.

Biological control has been considered a sustainable alternative to combat phytopathogens. The increase of studies in the past few years involving Actinobacteria as biological control agents of phytopathogenic fungi has motivated us to search for which Actinobacteria genus that have been studied in the last five years and explore their mechanisms of antifungal activity. The accesses were carried out on three multidisciplinary digital platforms: PubMED/MedLine, Web of Science and Scopus. Actinobacteria from genus Amycolatopsis, Curtobacterium, Kocuria, Nocardioides, Nocardiopsis, Saccharopolyspora, Streptoverticillium and especially Streptomyces showed a broad antifungal spectrum through several antibiosis mechanisms such as the production of natural antifungal compounds, siderophores, extracellular hydrolytic enzymes and activation of plant defense system. We observed the formation of a methodology based on antagonistic compounds bioactivity to select efficient Actinobacteria to be used as biological control agents against phytopathogenic fungi. The use of multifunctional Actinobacteria has been proven to be efficient, not only by its natural protective activity against phytopathogenic fungi but also because of their ability to act as plant growth-promoting bacteria.

Optimisation of DNA electroporation protocols for different plant-associated bacteria.

Electroporation is a vital process that facilitates the use of modern recombineering and other high-throughput techniques in a wide array of microorganisms, including non-model bacteria like plant growth-promoting bacteria (PGPB). These microorganisms play a significant role in plant health by colonizing plants and promoting growth through nutrient exchange and hormonal regulation. In this study, we introduce a sequential Design of Experiments (DOE) approach to obtain highly competent cells swiftly and reliably for electroporation. Our method focuses on optimizing the three stages of the electroporation procedure-preparing competent cells, applying the electric pulse field, and recovering transformed cells-separately. We utilized a split-plot fractional design with five factors and a covariate to optimize the first step, response surface methodology (RSM) for the second step, and Plackett-Burman design for two categorical factors and one continuous factor for the final step. Following the experimental sequence with three bacterial models, we achieved efficiencies 10 to 100 times higher, reaching orders of 105 to 106 CFU/µg of circular plasmid DNA. These results highlight the significant potential for enhancing electroporation protocols for non-model bacteria.

Less is more: A new strategy combining nanomaterials and PGPB to promote plant growth and phytoremediation in contaminated soil.

Novel combination strategies of nanomaterials (NMs) and plant growth-promoting bacteria (PGPB) may facilitate soil remediation and plant growth. However, the efficiency of the NM-PGPB combination and interactions among NMs, PGPB, and plants are still largely unknown. We used multiwalled carbon nanotubes (MWCNTs) and zero-valent iron (nZVI) combined with Bacillus sp. PGP5 to enhance the phytoremediation efficiency of Solanum nigrum on heavy metal (HM)-contaminated soil. The NM-PGPB combination showed the best promoting effect on plant growth, which also had synergistic effects on the bioaccumulation of HMs in S. nigrum. The MWCNT-PGP5 combination increased the Cd, Pb, and Zn removal efficiency of S. nigrum by 62.03%, 69.44%, and 61.31%, respectively. The underlining causes of improved plant growth and phytoremediation by NMs-PGPB combination were further elucidated. NM application promoted PGPB survival in soil. Compared with each single application, the combined application minimized disturbance to plant transcription levels and rhizosphere microbial community, resulting in the best performance on soil remediation and plant growth. The NM-PGPB-induced changes in the microbial community and root gene expression were necessary for plant growth promotion. This work reveals the "less is more" advantage of the NM-PGPB combination in soil remediation, providing a new strategy for soil management.

Peribacillus frigoritolerans T7-IITJ, a potential biofertilizer, induces plant growth-promoting genes of Arabidopsis thaliana.

AIMS: This study aimed to isolate plant growth and drought tolerance-promoting bacteria from the nutrient-poor rhizosphere soil of Thar desert plants and unravel their molecular mechanisms of plant growth promotion. METHODS AND RESULTS: Among our rhizobacterial isolates, Enterobacter cloacae C1P-IITJ, Kalamiella piersonii J4-IITJ, and Peribacillus frigoritolerans T7-IITJ, significantly enhanced root and shoot growth (4-5-fold) in Arabidopsis thaliana under PEG-induced drought stress. Whole genome sequencing and biochemical analyses of the non-pathogenic bacterium T7-IITJ revealed its plant growth-promoting traits, viz., solubilization of phosphate (40-73 µg/ml), iron (24 ± 0.58 mm halo on chrome azurol S media), and nitrate (1.58 ± 0.01 µg/ml nitrite), along with production of exopolysaccharides (125 ± 20 µg/ml) and auxin-like compounds (42.6 ± 0.05 µg/ml). Transcriptome analysis of A. thaliana inoculated with T7-IITJ and exposure to drought revealed the induction of 445 plant genes (log2fold-change > 1, FDR < 0.05) for photosynthesis, auxin and jasmonate signalling, nutrient uptake, redox homeostasis, and secondary metabolite biosynthesis pathways related to beneficial bacteria-plant interaction, but repression of 503 genes (log2fold-change < -1) including many stress-responsive genes. T7-IITJ enhanced proline 2.5-fold, chlorophyll 2.5-2.8-fold, iron 2-fold, phosphate 1.6-fold, and nitrogen 4-fold, and reduced reactive oxygen species 2-4.7-fold in plant tissues under drought. T7-IITJ also improved the germination and seedling growth of Tephrosia purpurea, Triticum aestivum, and Setaria italica under drought and inhibited the growth of two plant pathogenic fungi, Fusarium oxysporum, and Rhizoctonia solani. CONCLUSIONS: P. frigoritolerans T7-IITJ is a potent biofertilizer that regulates plant genes to promote growth and drought tolerance.

Molecular Insights into Plant-Microbe Interactions: A Comprehensive Review of Key Mechanisms.

In most ecosystems, plants establish complex symbiotic relationships with organisms, such as bacteria and fungi, which significantly influence their health by promoting or inhibiting growth. These relationships involve biochemical exchanges at the cellular level that affect plant physiology and have evolutionary implications, such as species diversification, horizontal gene transfer, symbiosis and mutualism, environmental adaptation, and positive impacts on community structure and biodiversity. For these reasons, contemporary research, moving beyond observational studies, seeks to elucidate the molecular basis of these interactions; however, gaps in knowledge remain. This is particularly noticeable in understanding how plants distinguish between beneficial and antagonistic microorganisms. In light of the above, this literature review aims to address some of these gaps by exploring the key mechanisms in common interspecies relationships. Thus, our study presents novel insights into these evolutionary archetypes, focusing on the antibiosis process and microbial signaling, including chemotaxis and quorum sensing. Additionally, it examined the biochemical basis of endophytism, pre-mRNA splicing, and transcriptional plasticity, highlighting the roles of transcription factors and epigenetic regulation in the functions of the interacting organisms. These findings emphasize the importance of understanding these confluences in natural environments, which are crucial for future theoretical and practical applications, such as improving plant nutrition, protecting against pathogens, developing transgenic crops, sustainable agriculture, and researching disease mechanisms. It was concluded that because of the characteristics of the various biomolecules involved in these biological interactions, there are interconnected molecular networks in nature that give rise to different ecological scaffolds. These networks integrate a myriad of functionally organic units that belong to various kingdoms. This interweaving underscores the complexity and multidisciplinary integration required to understand plant-microbe interactions at the molecular level. Regarding the limitations inherent in this study, it is recognized that researchers face significant obstacles. These include technical difficulties in experimentation and fieldwork, as well as the arduous task of consolidating and summarizing findings for academic articles. Challenges range from understanding complex ecological and molecular dynamics to unbiased and objective interpretation of diverse and ever-changing literature.

Halotolerant PGPB Staphylococcus sciuri ET101 protects photosynthesis through activation of redox dissipation pathways in Lycopersicon esculentum.

Photosynthesis is known to be seriously affected by salt stress. The stress induced membrane damage leads to disrupted photosynthetic components causing imbalance between production and utilization of ATP/NADPH with generation of ROS leading to photoinhibition and photodamage. In the current study, role of halotolerant plant growth promoting bacteria (PGPB) Staphylococcus sciuri ET101 in protection of photosynthesis in tomato plants during salinity stress was evaluated by analysing changes in antioxidant defense and activation of redox dissipation pathways. Inoculation of S. sciuri ET101 significantly enhanced the growth of tomato plants with significantly higher photosynthetic rates (PN) under normal and salinity stress conditions. Further, increased membrane stability, soluble sugar accumulation and significant decrease in malondialdehyde (MDA) content in leaves of ET101 inoculated tomato plants under normal and salinity were observed along with increased expression of antioxidant genes for efficient ROS detoxification and suppression of oxidative damage. Additionally, salinity induced decrease in rate of photosynthesis (PN) due to lowered chloroplastic CO2 concentration (Cc) attributed by low mesophyll conductance (gm) in uninoculated plants was alleviated by ET101 inoculation showing significantly higher carboxylation rate (Vcmax), RuBP generation (Jmax) and increased photorespiration (PR). The genes involved in photorespiratory process, cyclic electron flow (CEF), and alternative oxidase (AOX) pathway of mitochondrial respiration were abundantly expressed in leaves of ET101 inoculated plants indicating their involvement in protecting photosynthesis from salt stress induced photoinhibition. Collectively, our results indicated that S. sciuri ET101 has the potential in protecting photosynthesis of tomato plants under salinity stress through activation of redox dissipation pathways.

Zero budget natural farming components Jeevamrit and Beejamrit augment Spinacia oleracea L. (spinach) growth by ameliorating the negative impacts of the salt and drought stress.

The growth of crop plants, particularly spinach (Spinacia oleracea L.), can be significantly impeded by salinity and drought. However, pre-treating spinach plants with traditional biofertilizers like Jeevamrit and Beejamrit (JB) substantially reverses the salinity and drought-induced inhibitory effects. Hence, this study aims to elucidate the underlying mechanisms that govern the efficacy of traditional fertilizers. The present work employed comprehensive biochemical, physiological, and molecular approaches to investigate the processes by which JB alleviates abiotic stress. The JB treatment effectively boosts spinach growth by increasing nutrient uptake and antioxidant enzyme activity, which mitigates the detrimental effects of drought and salinity-induced stress. Under salt and drought stress conditions, the application of JB resulted in an impressive rise in germination percentages of 80 and 60%, respectively. In addition, the application of JB treatment resulted in a 50% decrease in electrolyte leakage and a 75% rise in the relative water content of the spinach plants. Furthermore, the significant reduction in proline and glycine betaine levels in plants treated with JB provides additional evidence of the treatment's ability to prevent cell death caused by environmental stressors. Following JB treatment, the spinach plants exhibited substantially higher total chlorophyll content was also observed. Additionally, using 16S rRNA sequencing, we discovered and characterized five plant-beneficial bacteria from the JB bio-inoculants. These bacterial isolates comprise a number of traits that contribute to growth augmentation in plants. These evidences suggest that the presence of the aforesaid microorganisms (along with additional ones) is accountable for the JB-mediated stimulation of plant growth and development.

Perspective on utilization of Bacillus species as plant probiotics for different crops in adverse conditions.

Plant probiotic bacteria are a versatile group of bacteria isolated from different environmental sources to improve plant productivity and immunity. The potential of plant probiotic-based formulations is successfully seen as growth enhancement in economically important plants. For instance, endophytic Bacillus species acted as plant growth-promoting bacteria, influenced crops such as cowpea and lady's finger, and increased phytochemicals in crops such as high antioxidant content in tomato fruits. The present review aims to summarize the studies of Bacillus species retaining probiotic properties and compare them with the conventional fertilizers on the market. Plant probiotics aim to take over the world since it is the time to rejuvenate and restore the soil and achieve sustainable development goals for the future. Comprehensive coverage of all the Bacillus species used to maintain plant health, promote plant growth, and fight against pathogens is crucial for establishing sustainable agriculture to face global change. Additionally, it will give the latest insight into this multifunctional agent with a detailed biocontrol mechanism and explore the antagonistic effects of Bacillus species in different crops.

Distinct interactions of ericoid mycorrhizae and plant growth-promoting bacteria: impacts on blueberry growth and heat resilience.

Blueberries confront substantial challenges from climate change, such as rising temperatures and extreme heat, necessitating urgent solutions to ensure productivity. We hypothesized that ericoid mycorrhizal fungi (ErM) and plant growth-promoting bacteria (PGPB) would establish symbiotic relationships and increase heat stress tolerance in blueberries. A growth chamber study was designed with low (25/20°C) and high temperature (35/30°C) conditions with micropropagated blueberry plantlets inoculated with ErM, PGPB, and both. Gas exchange and chlorophyll fluorescence properties of the leaves were monitored throughout the growth. At harvest, biochemical assays and biomass analysis were performed to evaluate potential oxidative stress induced by elevated temperatures. ErM application boosted root biomass under 25/20°C conditions but did not impact photosynthetic efficiency. In contrast, PGPB demonstrated a dual role: enhancing photosynthetic capacity and reducing stomatal conductance notably under 35/30°C conditions. Moreover, PGPB showcased conflicting effects, reducing oxidative damage under 25/20°C conditions while intensifying it during 47°C heat shock. A significant highlight lies in the opposing effects of ErM and PGPB on root growth and stomatal conductance, signifying their reciprocal influence on blueberry plant behavior, which may lead to increased water uptake or reduced water use. Understanding these complex interactions holds promise for refining sustainable strategies to overcome climate challenges.

Nitrogen fertilization regulates crosstalk between marandu palisadegrass and Herbaspirillum seropedicae: An investigation based on 15N isotopic analysis and root morphology.

Strategies seeking to increase the use efficiency of nitrogen (N) fertilizers and that benefit plant growth through multiple mechanisms can reduce production costs and contribute to more sustainable agriculture free of polluting residues. Under controlled conditions, we investigated the compatibility between foliar inoculation with an endophytic diazotrophic bacterium (Herbaspirillum seropedicae HRC54) at control and low, medium and high N fertilization levels (0, 25, 50 and 100 mg of N kg-1 as urea, respectively) in Marandu palisadegrass. Common procedures in our research field (biometric and nutritional assessments) were combined with isotopic techniques (natural abundance - δ15N‰ and 15N isotope dilution) and root scanning to determine the contribution of fixed N and recovery of N fertilizer by the grass. Overall, the combined use of 15N isotopic techniques revealed that inoculation not only improved the recovery of applied N-urea from the soil but also provided fixed nitrogen to Marandu palisade grass, resulting in an increase in the total accumulated N. When inoculated plants grew at control and low levels of N, a positive cascade effect encompassing root growth stimulation (nodes of smaller diameter roots), better soil and fertilizer resource exploitation and increased forage production was observed. In contrast, increasing N reduced the contributions of N fixed by H. seropedicae from 21.5% at the control level to 8.6% at the high N level. Given the minimal to no observed growth promotion, this condition was deemed inhibitory to the positive effects of H. seropedicae. We discuss how to make better use of H. seropedicae inoculation in Marandu palisadegrass, albeit on a small scale, thus contributing to a more rational and efficient use of N fertilizers. Finally, we pose questions for future investigations based on 15N isotopic techniques under field conditions, which have great applicability potential.