Rhizosphere Bacteria in Plant Growth Promotion, Biocontrol, and Bioremediation of Contaminated Sites: A Comprehensive Review of Effects and Mechanisms

Synergistic interaction of sodium nitroprusside and Serratia marcescens in mitigation of nematode stress in tomato

Plant growth and development are negatively impacted by root-knot nematodes (RKNs), which in turn affects plant production. Chemical nematicides are one of the effective strategies for managing RKNs. But, high concentration of these chemicals is toxic to plants, environment and humans. Therefore, an in-vivo study was conducted to unravel the synergistic interplay sodium nitroprusside (SNP: nitric oxide donor) and, Serratia marcescens in M. incognita-stressed tomato plants. Results revealed that treatment with SNP and bacterial culture cells reduced gall formation and improved morphology. It also reduced nematode-induced oxidative stress in M. incognita-infested tomato plants as compared to untreated plants. Increased photosynthetic parameters including photosynthetic pigments and gas-exchange parameters was also observed in treated plants. Additionally, treated plants exhibited increased antioxidant defense system in terms of upregulated activities of enzymatic antioxidants (Ascorbate peroxidase, guaiacol peroxidase, polyphenol oxidase, catalase, glutathione-S-transferase and superoxide dismutase). Content of non-enzymatic antioxidants (Glutathione, ascorbic acid and tocopherol) was also enhanced in treated plants as compared to untreated nematode-infected plants. Further, treatment with SNP and S. marcescens increased secondary metabolites (total phenol, flavonoid and anthocyanin) and proline content. Reduction in nematode-induced nuclear and membrane damage was also observed in SNP and bacterial culture cells treated tomato plants. The integrative application of SNP and S. marcescens exhibited synergism and overpowered their individual application in reducing the negative effects of nematode stress. The findings of the current investigation suggest the integrative use of SNP and bacteria is more beneficial in alleviating nematode stress in plants.

Advancing crop resilience through nucleic acid innovations: rhizosphere engineering for food security and climate adaptation

Rhizosphere engineering has emerged as a transformative strategy to address the pressing challenges of climate change, food security, and environmental sustainability. By harnessing the dynamic interactions between plants and microbes, and environmental processes, this approach offers innovative solutions for enhancing crop production, protecting against pests and diseases, and remediating contaminated environments. This review explores how rhizosphere engineering, both plant-based and microbe-based, can be leveraged to enhance crop productivity, manage pests and diseases, and remediate contaminated environments under shifting climate conditions. We examine the effects of climate change drivers such as elevated CO2, increased N deposition, rising temperatures, and altered precipitation patterns, on plant-microbe interactions and rhizosphere processes. We show that climate change impacts key functions, including respiration, decomposition and stabilization of soil organic matter, nutrient cycling, greenhouse gas emissions, and microbial community dynamics. Despite these challenges, engineered rhizospheres can mitigate adverse effects of climate change by improving rhizodeposition, nitrogen fixation, root architecture modification, selective microbe recruitment, and pathogen control, while enhancing carbon allocation and stabilization in soil. However, the deployment of these technologies is not without challenges. Ecological risks, such as unintended gene transfer and disruption of native microbial communities, as well as socioeconomic barriers, must be carefully addressed to ensure safe and scalable implementation. We identify critical research gaps such as the limited understanding of multi-taxon cooperation and scalability in engineered rhizosphere systems, and how mechanistic understanding of designer plants and microbes can advance crop production, protection, and environmental remediation in agriculture and agroforestry under global changes.

Eco-safe potential of FITC-tagged nFeO in enhancing alfalfa-rhizobia symbiosis and salt stress tolerance via physicochemical and ultrastructural modifications

Salt stress severely limits global crop productivity by disrupting ionic balance, physiological processes, and cellular ultrastructure, particularly in salt-sensitive forages like alfalfa (Medicago sativa L). Addressing this issue requires environmentally feasible and innovative strategies. This study investigated the comparative potential of Nano-FeO and FeSO4 (30 mg kg-1) soil supplements with rhizobium on alfalfa salt tolerance employing morphological, physicochemical, and cellular approaches. The results demonstrated that FITC-nFeO and rhizobium significantly reduced Na+ uptake, enhanced K+ accumulation, and improved the Na+/K+ ratio in alfalfa roots and shoots relative to FeSO4. Scanning electron microscopy illustrated that FITC-nFeO ameliorated root ultracellular structure and leaf stomatal functionality, facilitating improved gaseous exchange characteristics and photosynthetic performance. Confocal laser scanning microscopy confirmed FITC-tagged nFeO adhesion to roots, supported by transmission electron microscopy findings of preserved chloroplast ultrastructure under FITC-nFeO and rhizobium application. FITC-nFeO also mitigated oxidative damage of ROS, as evidenced by reduced hydrogen peroxide, electrolyte leakage, and thiobarbituric acid reactive substances (TBARS) content, through enhanced antioxidant enzyme activities. Overall, in comparison to FeSO4, FITC-nFeO with rhizobium retrieved the salt-induced damages in alfalfa by promoting morpho-physiological and ultracellular integrity. This study highlights the role of nanotechnology in enhancing the resilience of forages on salt-contaminated soils, paving the way for eco-friendly remediation strategies.

Differentiation and Interconnection of the Bacterial Community Associated with Silene nigrescens Along the Soil-To-Plant Continuum in the Sub-Nival Belt of the Qiangyong Glacier

Plant microbiomes provide significant fitness advantages to their plant hosts, especially in the sub-nival belt. Studies to date have primarily focused on belowground communities in this region. Here, we utilized high-throughput DNA sequencing to quantify bacterial communities in the rhizosphere soil as well as in the root and leaf endosphere compartments of Silene nigrescens to uncover the differentiation and interconnections of these bacterial communities along the soil-to-plant continuum. Our findings reveal that the bacterial communities exhibit notable variation across different plant compartment niches: the rhizosphere soil, root endosphere, and leaf endosphere. There was a progressive decline in diversity, network complexity, network modularity, and niche breadth from the rhizosphere soil to the root endosphere, and further to the leaf endosphere. Conversely, both the host plant selection effect and the stability of these communities showed an increasing trend. Total nitrogen and total potassium emerged as crucial factors accounting for the observed differences in diversity and composition, respectively. Additionally, 3.6% of the total amplicon sequence variants (ASVs) were shared across the rhizosphere soil, root endosphere, and leaf endosphere. Source-tracking analysis further revealed bacterial community migration among these compartments. The genera Pseudomonas, IMCC26256, Mycobacterium, Phyllobacterium, and Sphingomonas constituted the core of the bacterial microbiome. These taxa are shared across all three compartment niches and function as key connector species. Notably, Pseudomonas stands out as the predominant taxon among these bacteria, with nitrogen being the most significant factor influencing its relative abundance. These findings deepen our understanding of the assembly principles and ecological dynamics of the plant microbiome in the sub-nival belt, offering an integrated framework for its study.

Shaping rhizocompartments and phyllosphere microbiomes and antibiotic resistance genes: The influence of different fertilizer regimes and biochar application

Understanding the impact of different soil amendments on microbial communities and antibiotic resistance genes (ARGs) dissemination is crucial for optimizing agricultural practices and mitigating environmental risks. This study investigated the effects of different fertilizer regimes and biochar on plant-associated bacterial communities and ARGs dissemination. The biochar's structural and chemical characteristics were characterized using scanning electron microscopy (SEM) and Fourier-transform infrared (FTIR) spectroscopy, revealing a porous architecture with diverse functional groups. The presence of ARGs varied significantly across groups, with manure-treated samples exhibiting the greatest diversity and abundance, raising concerns about ARGs dissemination. Soil enzyme activities responded differently to treatments; manure significantly enhanced catalase, acid phosphatase, and urease activities, whereas saccharase was most responsive to chemical fertilizer. These differences are possibly responsible for the distinct microbiome structure associated with the plant's root system. The analysis of bacterial diversity and richness across rhizocompartments and the phyllosphere highlighted that manure-treated rhizospheres and phyllospheres displayed the highest species richness and diversity. Notably, Proteobacteria dominated across most treatments, with distinct shifts in bacterial phyla and genera influenced by manure and biochar applications. The LEfSe analysis identified key indicator genera specific to each group, indicating that both fertilizer type and biochar application significantly shape microbial community composition. Co-occurrence network analysis further demonstrated that manure and biochar treatments created unique microbial networks in the rhizosphere, rhizoplane, phyllosphere, and endosphere, highlighting the role of these amendments in modulating microbial interactions in plant-associated environments. These findings suggest that manure, while enhancing microbial diversity and soil enzyme activities, also increases ARGs, whereas biochar may not contribute to the spread of ARGs and fosters distinct microbial communities, offering valuable insights for sustainable agricultural practices.

Quantitative tools for analyzing rhizosphere pH dynamics: localized and integrated approaches

The rhizosphere, the region surrounding plant roots, plays a critical role in nutrient acquisition, root development, and plant-soil interactions. Spatial variations in rhizosphere pH along the root axis are shaped by environmental cues, nutrient availability, microbial activity, and root growth patterns. Precise detection and quantification of these pH changes are essential for understanding plant plasticity and nutrient efficiency. Here, we present a refined methodology integrating pH indicator bromocresol purple with a rapid, non-destructive electrode-based system to visualize and quantify pH variations along the root axis, enabling high-resolution and scalable monitoring of root-induced pH changes in the rhizosphere. Using this approach, we investigated the impact of iron (Fe) availability on rhizosphere pH dynamics in wild-type (WT) and bHLH39-overexpressing (39Ox) seedlings. bHLH39, a key basic helix-loop-helix transcription factor in Fe uptake, enhances Fe acquisition when overexpressed, often leading to Fe toxicity and reduced root growth under Fe-sufficient conditions. However, its role in root-mediated acidification remains unclear. Our findings reveal that 39Ox plants exhibit enhanced rhizosphere acidification, whereas WT roots display zone-specific pH responses depending on Fe availability. To refine pH measurements, we developed two complementary electrode-based methodologies: localized rhizosphere pH change for region-specific assessment and integrated rhizosphere pH change for net root system variation. These techniques improve resolution, accuracy, and efficiency in large-scale experiments, providing robust tools for investigating natural and genetic variations in rhizosphere pH regulation and their role in nutrient mobilization and ecological adaptation.

Microbial diversity and interactions: Synergistic effects and potential applications of Pseudomonas and Bacillus consortia

Microbial diversity and interactions in the rhizosphere play a crucial role in plant health and ecosystem functioning. Among the myriads of rhizosphere microbes, Pseudomonas and Bacillus are prominent players known for their multifaceted functionalities and beneficial effects on plant growth. The molecular mechanism of interspecies interactions between natural isolates of Bacillus and Pseudomonas in medium conditions is well understood, but the interaction between the two in vivo remains unclear. This paper focuses on the possible synergies between Pseudomonas and Bacillus associated in practical applications (such as recruiting beneficial microbes, cross-feeding and niche complementarity), and looks forward to the application prospects of the consortium in agriculture, human health and bioremediation. Through in-depth understanding of the interactions between Pseudomonas and Bacillus as well as their application prospects in various fields, this study is expected to provide a new theoretical basis and practical guidance for promoting the research and application of rhizosphere microbes.

Effects of treating wheat (Triticum aestivum) seedling roots with Azospirillum lectins to improve abiotic stress tolerance

While the effects of plant growth-promoting rhizobacterium, Azospirillum , on abiotic stress tolerance in plants are widely reported, the mechanisms that underlie this process remain elusive. Surface lectins of strains A. brasilense Sp7 and A. baldaniorum Sp245 are capable of attaching to specific carbohydrates and ensure the binding of bacteria to the surface of the plant root. They exhibit multifunctionality, and the effects induced by lectins are dose-dependent. This work investigated mechanisms by which lectins improved drought tolerance in wheat (Triticum aestivum ) plants. In the roots of wheat seedlings under drought stress, lectins with varying intensities increased the activity of peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT). Lectins caused a decrease in lipid peroxidation, but increased the content of secondary metabolites such as total phenolics and flavonoids. In the roots of stressed seedlings, lectins increased the total protein content and caused a dose-dependent change in the electrophoretic spectra of low molecular weight proteins. It was concluded that Azospirillum lectins, due to their ability to influence the metabolism of the host plant, are involved in adaptive changes in the roots of wheat seedlings. Lectins can regulate the relationship between bacteria and their hosts when soil and climatic factors change.

Bacterial dynamics and exchange in plant-insect interactions

In nature, plants and insects engage in intricate interactions. Despite the increasing knowledge of the microbiomes of plants and insects, the extent to which they exchange and alter each other's microbiomes remains unclear. In this work, the bacterial community associated with nymphs of Philaenus spumarius (Hemiptera: Aphrophoridae), the stems of Coleostephus myconis where the nymphs were feeding, and the foam produced by the nymphs, were studied by culture-dependent and -independent approaches, with an attempt to elucidate the exchange of bacteria between plants and insects. The results suggest that both approaches complement each other, as many bacterial genera identified by metabarcoding were not detected by culturing, and vice versa. Overall, stems and foam exhibited higher bacterial diversity than nymphs, with all the samples showing enrichment in bacteria known to provide diverse benefits to their host. Stems and foam were the most similar in bacterial composition, but Burkholderiaceae and Moraxellaceae dominated the stems, whereas Rhizobiaceae and Sphingobacteriaceae dominated the foam. Nymphs exhibit the most distinct bacterial composition, yet more similar to that found in the stem compared to the foam. Indeed, nymphs were enriched on endosymbiotic bacteria, mostly Candidatus Sulcia and Sodalis, not found in the stem and foam. Nevertheless, during feeding, nymphs appeared to exchange several bacteria genera with C. myconis, with a significant number being incorporated into the bacteriome of the nymph. The genera Curvibacter, Cutibacterium, Methylobacterium, Pseudomonas and Rhizobium are likely the most exchanged. Nymphs also appear to exchange bacteria to the foam, notably species from the Enhydrobacter, Pseudomonas, Rhizobium and Roseomonas genera. More studies to infer the functions of the shared bacteria between P. spumarius-C. myconis are needed.

Transcriptional reprogramming and microbiome dynamics in garden pea exposed to high pH stress during vegetative stage

MAIN CONCLUSION

High soil pH induces the upregulation of genes involved in oxidative stress and nutrient transport, while the enrichment of beneficial microbes (Variovorax, Chaetomium, and Pseudomonas) highlights their potential role in promoting stress adaptation. High soil pH severely impacts plant growth and productivity, yet the transcriptomic changes and microbial dynamics underlying stress adaptation in garden pea (Pisum sativum ssp. hortense) remain unclear. This study demonstrates that high soil pH leads to stunted growth, reduced biomass, impaired photosynthesis, and nutrient status in garden pea. Further, disruption in key nitrogen-fixing bacteria (Rhizobium indicum, R. leguminosarum, and R. redzepovicii), along with the downregulation of NifA and NifD genes and upregulation of NifH in nodules highlights the critical role of micronutrient balance in legume-microbe symbiosis and a compensatory response to maintain nitrogen status. RNA seq analysis revealed extensive transcriptional reprogramming in roots, characterized by the upregulation of oxidative stress response genes (e.g., oxidoreductase and glutathione transferase activities, metal ion transporters) and the downregulation of genes related to ammonia-lyase activity and ion binding, reflecting broader disruptions in nutrient homeostasis. KEGG pathway analysis identified enrichment of MAPK signaling pathway, likely interacting with other pathways associated with stress tolerance, metabolic adjustment, and structural reorganization as part of adaptive responses to high pH. Root microbiome analysis showed significant enrichment of Variovorax, Shinella, and Chaetomium, suggesting host-driven recruitment under high pH stress. Stable genera, such as Pseudomonas, Novosphingobium, Mycobacterium, Herbaspirillum, and Paecilomyces, displayed resilience to stress conditions, potentially forming core microbiome components for adaptation to high pH. In a targeted study, inoculation of plants with an enriched microbiome, particularly C. globosum, under high pH conditions improved growth parameters and increased the abundance of Stenotrophomonas and Pseudomonas in the roots. It suggests that these bacterial genera may act as helper microbes to C. globosum, collectively promoting stress resilience in pea plants suffering from high pH. These findings provide a foundation for microbiome-aided breeding programs and the development of microbial consortia to enhance the adaptation of pea plants to high pH conditions.

Tripartite microbial augmentation of Bradyrhizobium diazoefficiens, Bacillus sp. MN54, and Piriformospora indica on growth, yield, and nutrient profiling of soybean (Glycine max L.)

Introduction

Enhancing productivity and nutrient content of soybean (Glycine max L.) is vital for sustainable agriculture. The utilization of beneficial bacterial and fungal strains has shown promising results in promoting plant growth and improving nutrient uptake. However, the effects of the individual and interactions of such microbes on soybean growth, yield, and nutrient profiling remain inadequately understood. Thus, there is a pressing need to comprehensively investigate the impact of tripartite microbial augmentation on soybean cultivation.

Methods

This field study aims to elucidate the synergistic mechanisms underlying the interactions between Bacillus sp. MN54, Bradyrhizobium diazoefficiens, and Piriformospora indica and their collective influence on soybean growth parameters, yield and nutritional quality.

Results

In vivo compatibility tests revealed that consortium applications led to a maximum of 90% soybean germination. The field study demonstrated a significant increase in plant height (17.01%), nodules plant-1 (17.35%), pods plant-1 (12.11%), and grain yield (20.50%) due to triple inoculation over untreated control. The triple inoculation also significantly increased chlorophyll a, b, and leghemoglobin contents by 19.38, 21.01, and 14.28%, respectively, compared to control. Triple inoculation promoted crude fiber, protein, and oil content by 14.92, 8.78, and 10.52%, respectively, compared to the untreated control. The increase in nitrogen content by 7.33% in grains and 6.26% in stover and phosphorus by 11.31% in grains and 12.72% in stover was observed through triple application over untreated control.

Discussion

Our findings highlight the potential of microbial inoculants as biofertilizers in sustainable soybean production. The triple inoculation with Bacillus sp. MN54, Bradyrhizobium diazoefficiens, and Piriformospora indica significantly improved soybean growth, yield, grain quality attributes, and nutrient uptake. This microbial consortium application could help to enhance agricultural productivity by boosting the nodulation in soybean and improving synergism between the microbial strains.

Unveiling remarkable bacterial diversity trapped by cowpea (Vigna unguiculata) nodules inoculated with soils from indigenous lands in Central-Western Brazil

Cowpea (Vigna unguiculata) is recognized as a promiscuous legume in its symbiotic relationships with rhizobia, capable of forming associations with a wide range of bacterial species. Our study focused on assessing the diversity of bacterial strains present in cowpea nodules when inoculated with soils from six indigenous lands of Mato Grosso do Sul state, Central-Western Brazil, comprising the Cerrado and the Pantanal biomes, which are known for their rich diversity. The DNA profiles (BOX-PCR) of 89 strains indicated great genetic diversity, with 20 groups and 23 strains occupying single positions, and all strains grouped at a final similarity level of only 25%. Further characterization using 16S rRNA gene sequencing revealed a diverse array of bacterial genera associated with the cowpea nodules. The strains (number in parenthesis) were classified into ten genera: Agrobacterium (47), Ancylobacter (2), Burkholderia (12), Ensifer (1), Enterobacter (1), Mesorhizobium (1), Microbacterium (1), Paraburkholderia (1), Rhizobium (22), and Stenotrophomonas (1), split into four different classes. Notably, only Ensifer, Mesorhizobium, Rhizobium, and Paraburkholderia are classified as rhizobia. Phylogenetic analysis was conducted based on the classes of the identified genera and the type strains of the closest species. Our integrated analyses, combining phenotypic, genotypic, and phylogenetic approaches, highlighted the significant promiscuity of cowpea in associating with a diverse array of bacteria within nodules, showcasing the Brazilian soils as a hotspot of bacterial diversity.

Antifungal efficacy and mechanisms of Bacillus licheniformis BL06 against Ceratocystis fimbriata

Sweet potato black rot caused by the pathogenic fungus Ceratocystis fimbriata is a destructive disease that can result in severe agricultural losses. This study explores the antifungal efficacy and underlying mechanisms of Bacillus licheniformis BL06 against C. fimbriata. The plate antagonism assay revealed that BL06 significantly suppressed the radial growth of C. fimbriata mycelia, achieving inhibition rates of 39.53%, 53.57%, 64.38%, and 69.11% after 7, 10, 13, and 16 days, respectively. In vivo experiments demonstrated that BL06-treated sweet potato tissues exhibited markedly smaller lesions than the control, indicating effective suppression of black rot. Microscopic observations indicated that BL06 treatment altered the morphology and activity of C. fimbriata mycelia, causing swelling and deformation. Additionally, BL06 markedly reduced spore production and germination in a dose-dependent manner, with complete inhibition observed at the highest concentrations tested. The cell-free supernatant (CFS) of BL06 was identified as the primary antifungal agent, achieving an inhibition rate of 76.11% on mycelial growth. Transcriptome analysis of C. fimbriata treated with BL06 CFS revealed significant downregulation of genes involved in cell wall and membrane biosynthesis, spore development, protein processing in the endoplasmic reticulum, and energy metabolism. These findings suggest that BL06 is a potent biocontrol agent against C. fimbriata, exerting its effects through multiple molecular pathways.

Tolerance and antioxidant response to heavy metals are differentially activated in Trichoderma asperellum and Trichoderma longibrachiatum

Heavy metal pollution reduces the community of soil microorganisms, including fungi from the genus Trichoderma, which are plant growth promotors and biological control agents. Because of potential effects on crop productivity, the toxic effects of heavy metals (HMs) in Trichoderma are of interest. However, there have been few studies on the biochemical and molecular response to oxidation caused by exposure to copper (Cu), chromium (Cr), and lead (Pb) and whether this antioxidant response is species-specific. In this study, we compared the tolerance of Trichoderma asperellum and Trichoderma longibrachiatum to Cu, Pb, and Cr and evaluated the expression of genes related to the antioxidant response, including glutathione peroxidase (GPX), catalase (CAT), and cysteine synthase (CYS) as well as the activity of peroxidase and catalase. The isolates of Trichoderma were selected because we previously reported them as promotors of plant growth and agents of biological control. Our results revealed that, with exposure to the three HMs, the Trichoderma cultures formed aggregates and the culture color changed according to the metal and the Trichoderma species. The tolerance index (TI) indicated that the two Trichoderma species were tolerant of HMs (Cu > Cr > Pb). However, the TI and conidia production revealed that T. longibrachiatum was more tolerant of HMs than T. asperellum. The three HMs caused oxidative damage in both Trichoderma species, but the enzyme activity and gene expression were differentially regulated based on exposure time (72 and 144 h) to the HMs and Trichoderma species. The main changes occurred in T. asperellum; the maximum expression of the GPX gene occurred at 144 h in response to all three HMs, whereas the CAT gene was upregulated at 72 h in response to Cu but downregulated at 144 h in response to all three HMs. The CYS gene was upregulated in response to the three metals. The peroxidase activity increased with all three HMs, but the catalase activity increased with Cu and Pb at 72 h and decreased at 144 h with Pb and Cr. In T. longibrachiatum, the GPX gene was upregulated with all three HMs at 72 h, the CAT gene was upregulated only with Pb at 72 h and was downregulated at 144 h with HMs. Cr and Cu upregulated CYS gene expression, but expression did not change with Pb. The peroxidase activity increased with Cu at 144 h and with Cr at 72 h, whereas Pb decreased the enzyme activity. In contrast, catalase activity increased with the three metals at 144 h. In conclusion, T. longibrachiatum was more tolerant of Cu, Cr, and Pb than was T. asperellum, but exposure to all three HMs caused oxidative damage to both Trichoderma species. Peroxidases and catalases were activated, and the expression of the genes GPX and CYS was upregulated, whereas the CAT gene was downregulated. These findings indicate that the antioxidant response to HMs was genetically modulated in each Trichoderma species.

Plant growth-promoting microorganisms as natural stimulators of nitrogen uptake in citrus

Improving nitrogen uptake efficiency by citrus in Mediterranean areas, where this crop predominates, is crucial for reducing ground-water pollution and enhancing environmental sustainability. This aligns with the Farm to Fork Strategy (European Green Deal) objectives, which aim to reduce the use of mineral fertilizers by up to 20% and to eliminate soil contamination from nitrogen entirely. In this context, exploring the potential of plant growth-promoting bacteria application to reduce nutrient inputs is a promising opportunity. The objective of the present study was to evaluate the effect of two Bacillus subtilis strains either individually inoculated or in combination with Saccharomyces cerevisiae on 15N-labeled fertilizer uptake efficiency and physiological parameters. Individual inoculations positively affected tree water potential, leaf chlorophyll concentrations (SPAD-values) and photosynthetic performance, enhancing tree growth. Fertilizer-15N use efficiency increased, as did phosphorus and potassium uptakes. Conversely, no response was observed in the trees co-inoculated with S cerevisiae. Therefore, PGPB can be considered an interesting means to reduce reliance on synthetic fertilizers in citrus orchards, minimizing the environmental impact and promoting sustainable production practices.

Synergistic effects of allantoin and Achyranthes japonica-biochar profoundly alleviate lead toxicity during barley growth

Lead (Pb), a toxic metal, causes severe health hazards to both humans and plants due to environmental pollution. Biochar addition has been efficiently utilized to enhance growth of plants as well as yield in the presence of Pb-induced stress. The present research introduces a novel use of biochar obtained from the weed Achyranthes japonica to enhance the growth of plants in Pb-contaminated soil. An experiment was performed with 7 treatments: Control, Pb2+ (10 mg kg-1) only, biochar (4 %) only, allantoin (4 g kg-1) only, biochar combined with Pb2+, allantoin combined with biochar, as well as a combination of allantoin and biochar with Pb2+. Lead toxicity alone markedly diminished plant growth metrics, including root and shoot length, biomass (wet and dry), chlorophyll concentration, and grain production. The application of biochar, allantoin, or their joint administration markedly enhanced the length of shoots (by 50.3 %, 29 %, and 70 %), length of roots (by 69 %, 50 %, and 69 %), and fresh biomass of shoots (by 5 %, 29 %, and 5 %), respectively. This enhancement is ascribed to improved soil characteristics and more efficient absorption of nutrients. The application of biochar, allantoin and their combination improved the tolerance against Pb2+ by increasing the total chlorophyll level by 12 %, 16 %, and 17 %, respectively, vs. the control. Likewise, these amendments significantly (p < 0.05) improved the activity of antioxidant enzymes, including SOD, POD, and CAT by 49 %, 29 %, and 49 %, respectively. The resistance towards Pb2+ was enhanced by biochar, allantoin, and their combined application, with lower Pb2+ concentrations in shoots (59.9 %, 40.1 %, and 49.8 %), roots (48.2 %, 24.1 %, and 58.3 %), and grains (60.2 %, 29.7 %, and 40.1 %) compared to solely Pb-stress, respectively. In summary, converting the weed Achyranthes japonica into biochar and integrating it with allantoin provides an eco-friendly approach to control its proliferation while efficiently alleviating Pb-induced toxicity in plants.

Plant Colonization by Biocontrol Bacteria and Improved Plant Health: A Review

The use of biological control agents is one of the best strategies available to combat the plant diseases in an ecofriendly manner. Biocontrol bacteria capable of providing beneficial effect in crop plant growth and health, have been developed for several decades. It highlights the need for a deeper understanding of the colonization mechanisms employed by biocontrol bacteria to enhance their efficacy in plant pathogen control. The present review deals with the in-depth understanding of steps involved in host colonization by biocontrol bacteria. The colonization process starts from the root zone, where biocontrol bacteria establish initial interactions with the plant's root system. Moving beyond the roots, biocontrol bacteria migrate and colonize other plant organs, including stems, leaves, and even flowers. Also, the present review attempts to explore the mechanisms facilitating bacterial movement within the plant such as migrating through interconnected spaces such as vessels or in the apoplast, and applying quorum sensing or extracellular enzymes during colonization and what is needed to establish a long-term association within a plant. The impacts on microbial community dynamics, nutrient cycling, and overall plant health are discussed, emphasizing the intricate relationships between biocontrol bacteria and the plant's microbiome and the benefits to the plant's above-ground parts, the biocontrol 40 bacteria confer. By unraveling these mechanisms, researchers can develop targeted strategies for enhancing the colonization efficiency and overall effectiveness of biocontrol bacteria, leading to more sustainability and resilience.

Phosphorus-solubilizing fungi promote the growth of Fritillaria taipaiensis P. Y. Li by regulating physiological and biochemical reactions and protecting enzyme system-related gene expression

Introduction

Fritillaria taipaiensis P. Y. Li is a plant used to treat respiratory diseases such as pneumonia, bronchitis, and influenza. Its wild resources have become increasingly scarce, and the demand for efficient artificial cultivation has increased significantly in recent years. Phosphorus-solubilizing fungi can promote the dissolution of insoluble phosphate complex, which benefits plant nutrition. Another strategy for efficiently cultivating traditional Chinese medicine plants is to combine the soil with phosphorus-solubilizing fungi to provide nutrients and other desired features. This study aimed to investigate the effects of different phosphorus-solubilizing fungi and their combinations on photosynthesis, physiological and biochemical characteristics, and expression of protective enzyme system-related genes, and to find a reference strain suitable for the artificial cultivation and industrial development of F. taipaiensis P. Y. Li. In this study, the phosphorus-solubilizing fungi isolated from the rhizosphere soil of F. taipaiensis P. Y. Li were applied to the cultivation of F. taipaiensis P. Y. Li for the first time.

Methods

In this study, seven treatment groups (S1-S7) and one control group were set up using indoor pots as follows: S1 (inoculation with Aspergillus tubingensis), S2 (inoculation with A. niger), S3 (inoculation with Aspergillus nigerfunigatus) and S4 (inoculation with A. tubingensis and A. niger), S5 (inoculation with A. tubingensis and A. nigerfunigatus), S6 (inoculation with A. niger and A. nigerfunigatus), S7 (inoculation with A. tubingensis, A. niger, and A. nigerfunigatus), and CK (control group). These strains were inoculated into pots containing F. taipaiensis P. Y. Li bulbs,and the effects of different phosphorus-solubilizing fungi and combinations on the photosynthetic characteristics, basic physiological and biochemical indicators, and differential gene expression of protective enzyme systems in F. taipaiensis P. Y. Li leaves were determined.

Results

Most growth indexes showed significant differences in the fungal treatment groups compared with the CK group (P < 0.05). The stem diameter and plant height in the S5 group were the highest, which were 58.23% and 62.49% higher than those in the CK group, respectively. The leaf area in the S7 group was the largest, which increased by 141.34% compared with that in the CK group. Except for intercellular CO2 concentration (Ci), the contents of photosynthetic pigments, photosynthetic parameters, and amounts of osmoregulatory substances increased to varying degrees in the fungal treatment groups (P < 0.05). Among these, the S5 group had the highest stomatal conductance index and soluble sugar and free proline contents, whereas S6 had the highest chlorophyll a and soluble protein contents. In addition, the malondialdehyde (MDA) content in all inoculation groups was lower than that in the CK group. The MDA content was the lowest in S7, about 44.83% of that in the CK group. The activities of peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) were higher in all inoculation groups than those in the CK group; the changes in SOD and CAT activities were significant (P < 0.05). The expression levels of FtSOD, FtPOD, and FtCAT in the S5 group were the highest, which were 8.67, 7.65, and 6.08 times of those in the CK group, respectively.

Conclusion

Various combinations of phosphorus-solubilizing fungi exhibit differential capacities to enhance plant growth indices (including leaf area, plant height, and stem diameter), promote the accumulation of photosynthetic pigments, regulate osmotic pressure, and elevate antioxidant activity. Notably, The three fungal combinations (S7) were prone to cause a certain degree of antagonism, leading to suboptimal performances in certain biochemical indicators, such as free proline and POD levels. Our study pointed out that the S5 group inoculated with A. tubingensis and A. niger had the best overall effect. These experimental results provided a theoretical basis for the selection and development of artificial cultivation of F. taipaiensis P. Y. Li.

Combined application of rhizobacteria, organic and inorganic amendments reduce lead and cadmium uptake and improve growth of chickpea by modulating physiology and antioxidant status

Due to a lack of high-quality water, farmers have been compelled to use sewage water for irrigation, contaminating agricultural soils with multiple heavy metals. For the remediation of contaminated soil, plant growth-promoting rhizobacteria (PGPR), pressmud (PM), and iron (III) oxide were used to improve the growth and phytostabilization potential of chickpea grown in contaminated soil. Contaminated soil was collected from a nearby field, receiving sewage and factory water over the last 60 years. Chickpea seeds were inoculated with metal-tolerant (lead and cadmium) rhizobacterial and rhizobial strains. It was observed that combined application of rhizobia, rhizobacteria, iron oxide, and pressmud improved shoot fresh weight (87%), root fresh weight (47.9%), root length (47.9%), nodules plant-1 (2.58 folds), photosynthetic rate (63%) and grain yield (39%) of chickpea as compared to respective untreated control in contaminated soil. Moreover, a significant decrease in the lead (75.8 and 68.1%) and cadmium (81 and 72%) concentrations due to the combined application of rhizobacteria, rhizobia, iron oxide, and pressmud was observed in shoot and root of chickpea than respective control, respectively. It can be concluded that the contaminated soil with mixed metals can be remediated, and the growth and yield of chickpea can be improved.

Integration of physiology, genomics and microbiomics analyses reveal the biodegradation mechanism of petroleum hydrocarbons by Medicago sativa L. and growth-promoting bacterium Rhodococcus erythropolis KB1

Despite the effectiveness of microbial-phytoremediation for remediating total petroleum hydrocarbons (TPH)-contaminated soil, the underlying mechanisms remain elusive. This study investigated the whole-genome and biological activity of Rhodococcus erythropolis KB1, revealing its plant growth promotion (PGP), TPH degradation, and stress resistance capabilities. Phytoremediation (using alfalfa) and plant-microbial remediation (using alfalfa and KB1) were employed to degrade TPH. The highest TPH degradation rate, reaching 95%, was observed with plant-microbial remediation. This is attributed to KB1's ability to promote alfalfa growth, induce the release of signaling molecules to activate plant antioxidant enzymes, actively recruit TPH-degrading bacteria (e.g., Sphingomonas, Pseudomonas, C1-B045), and increase soil nitrogen and phosphorus levels, thereby accelerating TPH degradation by both plants and microorganisms. This study demonstrates that R. erythropolis KB1 holds great potential for enhancing the remediation of TPH-contaminated soil through its multifaceted mechanisms, particularly in plant-microbial remediation strategies, providing valuable theoretical support for the application of this technology.

Biodiversity and Antifungal Activities of Amazonian Actinomycetes Isolated from Rhizospheres of Inga edulis Plants

BACKGROUND

Actinobacteria are major producers of antibacterial and antifungal metabolites and are growing their search for substances of biotechnological interest, especially for use in agriculture, among other applications. The Amazon is potentially rich in actinobacteria; however, almost no research studies exist. Thus, we present a study of the occurrence and antifungal potential of actinobacteria from the rhizosphere of Inga edulis, a native South American plant and one that is economically useful in the whole of the Amazon.

METHODS

Among the 64 actinobacteria strains isolated from the rhizosphere of three Inga edulis plants, 20 strains were selected and submitted to dual-culture assays against five important phytopathogenic fungi and morphological and 16S rRNA gene analyses. Two strains, LaBMicrA B270 and B280, were also studied for production curves of metabolic extracts and antifungal activities, including their minimum inhibitory concentration (MIC) against phytopathogenic fungi.

RESULTS

Among the 20 strains, 90% were identified as Streptomyces and 10% as Kitasatospora. All the strains showed antagonisms against two or more of five phytopathogens: Corynespora cassiicola, Colletotrichum guaranicola, Colletotrichum sp., Pestalotiopsis sp., and Sclerotium coffeicola. Streptomyces spp. strains LaBMicrA B270 and B280 were active against phytopathogens of the guarana plant (Paullinia cupana). Furthermore, AcOEt/2-propanol 9:1 extract from the 10-day strain LaBMicrA B280 cultured medium presented activity against all the phytopathogens tested, with a minimum inhibitory concentration of 125 μg/mL.

CONCLUSIONS

The results revealed various actinomycetes in three rhizospheres of I. edulis in the Amazon and the high potential of metabolic extracts from some of these bacterial strains against phytopathogenic fungi that destroy numerous crops.

A multi-omics approach to unravel the interaction between heat and drought stress in the Arabidopsis thaliana holobiont

The impact of combined heat and drought stress was investigated in Arabidopsis thaliana and compared to individual stresses to reveal additive effects and interactions. A combination of plant metabolomics and root and rhizosphere bacterial metabarcoding were used to unravel effects at the plant holobiont level. Hierarchical cluster analysis of metabolomics signatures pointed out two main clusters, one including heat and combined heat and drought, and the second cluster that included the control and drought treatments. Overall, phenylpropanoids and nitrogen-containing compounds, hormones and amino acids showed the highest discriminant potential. A decrease in alpha-diversity of Bacteria was observed upon stress, with stress-dependent differences in bacterial microbiota composition. The shift in beta-diversity highlighted the pivotal enrichment of Proteobacteria, including Rhizobiales, Enterobacteriales and Azospirillales. The results corroborate the concept of stress interaction, where the combined heat and drought stress is not the mere combination of the single stresses. Intriguingly, multi-omics interpretations evidenced a good correlation between root metabolomics and root bacterial microbiota, indicating an orchestrated modulation of the whole holobiont.

Deciphering Molecular Mechanisms and Diversity of Plant Holobiont Bacteria: Microhabitats, Community Ecology, and Nutrient Acquisition

While gaining increasing attention, plant-microbiome-environment interactions remain insufficiently understood, with many aspects still underexplored. This article explores bacterial biodiversity across plant compartments, including underexplored niches such as seeds and flowers. Furthermore, this study provides a systematic dataset on the taxonomic structure of the anthosphere microbiome, one of the most underexplored plant niches. This review examines ecological processes driving microbial community assembly and interactions, along with the discussion on mechanisms and diversity aspects of processes concerning the acquisition of nitrogen, phosphorus, potassium, and iron-elements essential in both molecular and ecological contexts. These insights are crucial for advancing molecular biology, microbial ecology, environmental studies, biogeochemistry, and applied studies. Moreover, the authors present the compilation of molecular markers for discussed processes, which will find application in (phylo)genetics, various (meta)omic approaches, strain screening, and monitoring. Such a review can be a valuable source of information for specialists in the fields concerned and for applied researchers, contributing to developments in sustainable agriculture, environmental protection, and conservation biology.

Ecological influences of sulfadiazine on rhizosphere soil microbial communities in ryegrass (Lolium perenne L.)-soil potting systems: Perspectives on diversity, co-occurrence networks, and assembly processes

Microorganisms in the soil are crucial constituents of land ecosystems, significantly influencing their structure and functionality. However, the accumulation of antibiotics in agricultural practices may negatively affect these microbial communities. The objective of this study was to explore the ecological effects of the sulfonamide drug sulfadiazine (SDZ) on the rhizosphere soil microbial communities of ryegrass (Lolium perenne L.). A potting system experiment was constructed by exposing for 45 days after treatments with different initial concentrations of SDZ (0, 1, 10, and 30 mg/kg) to assess the effects of SDZ on soil microbial diversity, bacterial-fungal co-occurrence networks, and community assembly processes. The findings indicated that SDZ treatment significantly altered the community composition, especially for bacteria in the phylum Proteobacteria and Gemmatimonadota and fungi in the phylum Mortierellomycota and Aphelidiomycota. Network analysis revealed that SDZ stress caused alterations in microbial interaction patterns, especially at high treatment concentrations, and reduced network connectivity. In addition, SDZ significantly affected microbial community assembly processes, where stochastic processes were enhanced in bacterial communities, while fungal communities showed a balance of stochastic and deterministic processes. Analysis of environmental variables revealed that the presence of SDZ may disrupt the link between soil microorganisms and soil nitrogen compounds. The results provide new perspectives for understanding the ecological impacts of antibiotic residues in agroecosystems and provide a scientific basis for soil health management.

How to deal with xenobiotic compounds through environment friendly approach?

Every year, a huge amount of lethal compounds, such as synthetic dyes, pesticides, pharmaceuticals, hydrocarbons, etc. are mass produced worldwide, which negatively affect soil, air, and water quality. At present, pesticides are used very frequently to meet the requirements of modernized agriculture. The Food and Agriculture Organization of the United Nations (FAO) estimates that food production will increase by 80% by 2050 to keep up with the growing population, consequently pesticides will continue to play a role in agriculture. However, improper handling of these highly persistent chemicals leads to pollution of the environment and accumulation in food chain. These effects necessitate the development of technologies to eliminate or degrade these pollutants. Degradation of these compounds by physical and chemical processes is expensive and usually results in secondary compounds with higher toxicity. The biological strategies proposed for the degradation of these compounds are both cost-effective and eco-friendly. Microbes play an imperative role in the degradation of xenobiotic compounds that have toxic effects on the environment. This review on the fate of xenobiotic compounds in the environment presents cutting-edge insights and novel contributions in different fields. Microbial community dynamics in water bodies, genetic modification for enhanced pesticide degradation and the use of fungi for pharmaceutical removal, white-rot fungi's versatile ligninolytic enzymes and biodegradation potential are highlighted. Here we emphasize the factors influencing bioremediation, such as microbial interactions and carbon catabolism repression, along with a nuanced view of challenges and limitations. Overall, this review provides a comprehensive perspective on the bioremediation strategies.

Fostering climate-resilient agriculture with ACC-deaminase producing rhizobacterial biostimulants from the cold deserts of the Indian Himalayas

Climate change is one of the most significant threats to agricultural productivity, which necessitates a need for more resilient and sustainable farming practices. Rhizobacterial biostimulants that secrete 1-aminocyclopropane-1-carboxylate (ACC) deaminase and enhance crop resilience and yield can serve as a potential sustainable solution. The present study provides a comprehensive analysis of ACC-deaminase producing rhizobacteria (ACCD) isolated from cold deserts of the Indian trans-Himalayas and their efficacy to improve crop resilience and productivity under diverse climatic conditions. Thirty four efficient ACCD showed ACC deaminase activity ranging from 4.9 to 24484.3 nM α-ketobutyrate/h/mg/protein. These strains also exhibited broad-spectrum plant growth promotion (PGP) attributes, including tri-calcium phosphate (TCP) solubilization ranging from 2.4 to 687.5 μg/ml, siderophore production ranging from 62 to 224% and indole-3-acetic acid (IAA)-like auxin production ranging from 0.9 to 88.2 μg/ml. 16S rRNA gene sequencing of efficient strains showed their belonging to 10 genera, including Acinetobacter, Agrobacterium, Arthrobacter, Cellulomonas, Enterobacter, Microbacterium, Neomicrococcus, Priestia, Pseudomonas, and Rhizobium. Among these, Pseudomonas was the dominant genus with high ACC-deaminase activity and multiple PGP traits. These strains also showed growth under various stressed culture conditions, including acidity/alkalinity, different temperatures, desiccation, and salinity. Field applications of 4 efficient and stress-tolerant ACCD, including Pseudomonas geniculata, P. migulae, Priestia aryabhattai, and Rhizobium nepotum with reduced NPK dose under two different temperate climate conditions showed a significant improvement in growth and productivity of crops such as garlic, pea, potato, and wheat in slightly acidic soils and maize in saline-sodic alkaline soils. These findings indicated the broad-spectrum potential of these efficient and stress-tolerant ACCD strains to improve plant growth and productivity across diverse soil types and climatic conditions.

Eco-smart biocontrol strategies utilizing potent microbes for sustainable management of phytopathogenic diseases

Plants have an impact on the economy because they are used in the food and medical industries. Plants are a source of macro- and micronutrients for the health of humans and animals; however, the rise in microbial diseases has put plant health and yield at risk. Because there are insufficient controls, microbial infections annually impact approximately 25 % of the world's plant crops. Alternative strategies, such as biocontrol, are required to fight these illnesses. This review discusses the potential uses of recently discovered microorganisms because they are safe, effective, and unlikely to cause drug resistance. They have no negative effects on soil microbiology or the environment because they are environmentally benign. Biological control enhances indigenous microbiomes by reducing bacterial wilt, brown blotch, fire blight, and crown gall. More research is required to make these biocontrol agents more stable, effective, and less toxic before they can be used in commercial settings.

Synergistic Effect of Biochar, Phosphate Fertilizer, and Phosphorous Solubilizing Bacteria for Mitigating Cadmium (Cd) Stress and Improving Maize Growth in Cd-Contaminated Soil

Cadmium (Cd) contamination threatens human health and plant growth due to its accumulation in edible parts. The sole application of phosphorus-solubilizing bacteria (PSB), biochar (BC), and phosphorus (P) effectively mitigates Cd's adverse effects in contaminated agricultural systems. However, further investigation into their combined impacts on Cd toxicity and maize (Zea mays) production is essential. This study evaluates the synergistic effects of PSB (10 g kg-1 of Bacillus megaterium), BC (5% w/w), and P (0.8 g kg-1) on soil properties and the morphological and physiological traits of maize cultivated in agricultural soil contaminated with Cd (20 mg kg-1). The study revealed that Cd toxicity negatively impacts soil properties, reducing shoot and root biomass, lowering chlorophyll content, and heightening oxidative stress levels. Conversely, the combined use of P, PSB, and BC markedly improved soil properties, increasing the organic matter by 175.94%, available K by 87.24%, and available P by 306.93% compared to the control. This combination also improved maize growth metrics, with increases in aboveground dry biomass (92.98%), root dry biomass (110.33%), chlorophyll a (28.20%), chlorophyll b (108.34%), and total chlorophyll (37.17%). Notably, the treatment reduced Cd concentrations in maize leaves by 61.08% while increasing soil Cd levels by 31.12% compared to the control group. Overall, the synergistic effect of P-BC-PSB is an eco-friendly strategy for mitigating Cd toxicity in contaminated soil. However, further studies are required to explore its effects and molecular mechanisms on other crops.

Isolation and characterization of plant growth promoting rhizobacteria from cacti root under drought condition

Plant growth-promoting rhizobia (PGPR) helps plants grow and develop by protecting them from abiotic and biotic stresses, increasing the synthesis of chemicals that promote growth, and enabling the uptake of nutrients. Drought is one of the biggest problems throughout the world. The search for novel and efficient drought-resistant microorganisms that reduce the adverse effects executed by drought is a significant alternative. This study aimed to isolate and characterize PGPR strains from the Opuntia Ficus-Indica cactus plant's rhizosphere, cultivated in the semi-arid Shankargarh district of Uttar Pradesh, India. Tests for plant growth-promoting activity, such as the generation of indole acetic acid (IAA), phosphate solubilization, ammonia, carboxymethyl cellulase, and protease activity, were performed on all bacterial isolates. There were 246 bacterial strains isolated from the rhizospheric zone, and only 16.6 % showed drought resistance and various plant growth-promoting traits. The Bacillus sp. strain promoted the growth promotion of Capsicum annum L. under water stress (30 % field capacity). Additionally, Bacillus sp. isolates, with their potential for drought tolerance and plant growth promotion, could be applied in sustainable agriculture to enhance crop yield and resilience to water scarcity.

Impacts of root exudates on the toxic response of Chrysanthemum coronarium L. to the co-pollution of nanoplastic particles and tetracycline

Nano polystyrene (PS) particles and antibiotics universally co-exist, posing a threat to crop plants and hence human health, nevertheless, there is limited research on their combined toxic effects along with major influential factors, especially root exudates, on crop plants. This study aimed to investigate the response of Chrysanthemum coronarium L. to the co-pollution of nanoplastics and tetracycline (TC), as well as the effect of root exudates on this response. Based on a hydroponic experiment, the biochemical and physiological indices of Chrysanthemum coronarium L. were measured after 7 days of exposure. Results revealed that the co-pollution of TC and PS caused significant oxidative damage to the plants, resulting in reduced biomass. Amongst the two contaminants, TC played a more prominent role. PS could enter the root tissue, and the uptake of TC and PS by plant roots was synergetic. Malic acid, oxalic acid, and formic acid could explain 65.1% of the variation in biochemical parameters and biomass of the roots. These compounds affected the photosynthesis and biomass of Chrysanthemum coronarium L. by gradually lowering root reactive oxygen species (ROS) and leaf ROS. In contrast, the impact of rhizobacteria on the toxic response of the plants was relatively minor. These findings suggested that root exudates could alleviate the toxic response of plants to the co-pollution of TC and PS. This study enhances our understanding of the role of root exudates, providing insights for agricultural management and ensuring food safety.

Uptake, Translocation, Toxicity, and Impact of Nanoparticles on Plant Physiological Processes

The application of nanotechnology in agriculture has increased rapidly. However, the fate and effects of various nanoparticles on the soil, plants, and humans are not fully understood. Reports indicate that nanoparticles exhibit positive and negative impacts on biota due to their size, surface property, concentration within the system, and species or cell type under test. In plants, nanoparticles are translocated either by apoplast or symplast pathway or both. Also, it is not clear whether the nanoparticles entering the plant system remain as nanoparticles or are biotransformed into ionic forms or other organic compounds. Controversial results on the toxicity effects of nanomaterials on the plant system are available. In general, the nanomaterial toxicity was exerted by producing reactive oxygen species, leading to damage or denaturation of various biomolecules. The intensity of cyto- and geno-toxicity depends on the physical and chemical properties of nanoparticles. Based on the literature survey, it is observed that the effects of nanoparticles on the growth, photosynthesis, and primary and secondary metabolism of plants are both positive and negative; the response of these processes to the nanoparticle was associated with the type of nanoparticle, the concentration within the tissue, crop species, and stage of growth. Future studies should focus on addressing the key knowledge gaps in understanding the responses of plants to nanoparticles at all levels through global transcriptome, proteome, and metabolome assays and evaluating nanoparticles under field conditions at realistic exposure concentrations to determine the level of entry of nanoparticles into the food chain and assess the impact of nanoparticles on the ecosystem.

Growth regulation in bread wheat via novel bioinoculant formulation

Wheat (Triticum aestivum L.) is one of the most significant crops and the backbone of food security worldwide. However, low wheat production remains a substantial concern in global agricultural systems. It can be attributed to several factors, including adverse climatic conditions, plant disease and poor soil quality. Recent efforts have explored bioinoculant applications as a promising approach to enhance wheat yield, trying to mitigate constraints essential for future wheat production and global food security. This study tested talc powder, wheat biochar, sugarcane bagasse biochar, and farmyard manure as carriers with two endophytic bacterial strains, Burkholderia phytofirmans PsJN and Bacillus spp. MN54 was applied to three wheat varieties (Ujala-16, Zincol-16, and Fathejang-16). The data was recorded at the seedling and maturity growth stages of plants. A pot experiment revealed significant improvements in plant growth following bioinoculant application compared to controls. Notably, the combination of sugarcane bagasse biochar with Bacillus sp. MN54 exhibited the most pronounced effects, promoting internodal length, spike length, tiller number per plant, grain yield per plant, and spikelets per spike. Additionally, talc powder with Bacillus sp. MN54 increased peduncle length, tiller number per plant, and spike length in Fathejang-16. These findings offer valuable insights into optimizing bioinoculant formulations for improved agricultural practices, adapting to climate change, and contributing to ensuring global food security.

Elucidating the eco-friendly herbicidal potential of microbial metabolites from Bacillus altitudinis

Microbial herbicides play a vital role in agricultural preservation, amid growing concerns over the ecological impact from extensive development and use of chemical herbicides. Utilizing beneficial microbial metabolites to combat weeds has become a significant focus of research. This study focused on isolating herbicidal active compounds from Bacillus altitudinis D30202 through activity-guided methods. First, the n-butanol extract (n-BE) of B. altitudinis D30202 underwent fractionation using macroporous adsorption resin D101 and Sephadex LH-20, identifying Fr. F as the most potent segment against wild oats (Avena fatua L.). Ultra-performance liquid chromatography - quadrupole time-of-flight mass spectrometry (UPLC - QTOF-MS) identified nine compounds in the active fraction Fr. F. Subsequently, three subfractions (Fr.F-1 to Fr.F-3) were derived from Fr.F via semi-preparative liquid chromatography, resulting in methyl indole-3-acetate (MeIAA) purification. MeIAA, functioning as an auxin analog, exhibited effects of indole-3-acetic acid (IAA) on wild oats' growth, with a root length median inhibitory concentration of 81.06 µg/ml. Furthermore, we assessed MeIAA's herbicidal impact on five weed species across diverse families and genera, providing a first-time analysis of MeIAA's mechanism on wild oats. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed structural damage to leaves and roots post-MeIAA treatment. MeIAA treatment increased superoxide anion and hydrogen peroxide levels in wild oat roots, alongside with elevated peroxidase (POD) and superoxide dismutase (SOD) activity, chlorophyll-degrading enzymes (Chlase, MDACase), malondialdehyde (MDA) content, and relative conductivity in leaves. Conversely, it decreased catalase (CAT) activity and chlorophyll content. Therefore, this study provides a new material source and theoretical foundation for ecologically sustainable agricultural weed control.

Phytoremediation strategies for mitigating environmental toxicants

In natural environments, persistent pollutants such as heavy metals and organic compounds, are frequently sequestered in sediments, soils, and mineral deposits, rendering them biologically unavailable. This study examines phytoremediation, a sustainable technology that uses plants to remove pollutants from soil, water, and air. It discusses enhancing techniques such as plant selection, the use of plant growth-promoting bacteria, soil amendments, and genetic engineering. The study highlights the slow removal rates and the limited availability of plant species that are effective for specific pollutants. Furthermore, it investigates bioavailability and the mechanisms underlying root exudation and hyperaccumulation. Applications across diverse environments and innovative technologies, such as transgenic plants and nanoparticles, are also explored. Additionally, the potential for phytoremediation with bioenergy production is considered. The purpose of this study is to provide researchers, practitioners, and policymakers with valuable resources for sustainable solutions.

Genetic diversity, stress tolerance and phytobeneficial potential in rhizobacteria of Vachellia tortilis subsp. raddiana

BACKGROUND

Soil bacteria often form close associations with their host plants, particularly within the root compartment, playing a significant role in plant growth and stress resilience. Vachellia tortilis subsp. raddiana, (V. tortilis subsp. raddiana)a leguminous tree, naturally thrives in the harsh, arid climate of the Guelmim region in southern Morocco. This study aims to explore the diversity and potential plant growth-promoting (PGP) activities of bacteria associated with this tree.

RESULTS

A total of 152 bacterial isolates were obtained from the rhizosphere of V. tortilis subsp. raddiana. Rep-PCR fingerprinting revealed 25 distinct genomic groups, leading to the selection of 84 representative strains for further molecular identification via 16 S rRNA gene sequencing. Seventeen genera were identified, with Bacillus and Pseudomonas being predominant. Bacillus strains demonstrated significant tolerance to water stress (up to 30% PEG), while Pseudomonas strains showed high salinity tolerance (up to 14% NaCl). In vitro studies indicated variability in PGP activities among the strains, including mineral solubilization, biological nitrogen fixation, ACC deaminase activity, and production of auxin, siderophores, ammonia, lytic enzymes, and HCN. Three elite strains were selected for greenhouse inoculation trials with V. tortilis subsp. raddiana. Strain LMR725 notably enhanced various plant growth parameters compared to uninoculated control plants.

CONCLUSIONS

The findings underscore the potential of Bacillus and Pseudomonas strains as biofertilizers, with strain LMR725 showing particular promise in enhancing the growth of V. tortilis subsp. raddiana. This strain emerges as a strong candidate for biofertilizer formulation aimed at improving plant growth and resilience in arid environments.

Mitigation of heavy metal toxicity in pigeon pea by plant growth promoting Pseudomonas alcaliphila strain PAS1 isolated from contaminated environment

The risk of arsenic contamination is rising globally, and it has negative impacts on the physiological processes and growth of plants. Metal removal from contaminated soils can be accomplished affordably and effectively with plant growth promoting rhizobacteria (PGPR)-based microbial management. From this angle, this research evaluated the mitigation of arsenic toxicity using the bacteria isolated from contaminated site, Mettur, Salem district, South India. The newly isolated bacterial strain was screened for plant growth promotion potential and arsenic tolerance such as (100 ppm, 250 ppm, 500 ppm, 800 ppm and 1200 ppm). The metal tolerant rhizobacteria was identified using 16S rRNA gene sequence analysis as Pseudomonas alcaliphila strain PAS1 (GenBank accession number: OQ804624). Pigeon pea (Cajanus cajan) plants were used in pot culture experiments with varying concentrations of arsenic, (5 ppm, 10 ppm and 25 ppm) both with and without bacterial culture, for a period of 45 days. At the concentration of 25 ppm after the application of PAS1 enhanced the plant growth, protein and carbohydrate by 35.69%, 18.31% respectively. Interestingly, P. alcaliphila strain PAS1 significantly reduced the stress-induced elevated levels of proline, flavonoid, phenol and antioxidant enzyme in pigeon pea plants was 40%, 31.11%, 27.80% and 20.12%, respectively. Consequently, PAS1 may significantly reduce the adverse effects that arsenic causes to plant development in acidic soils, improve plant uptake of nutrients, and increase plant production. The findings of this study reveal that P. alcaliphila PAS1 is intrinsic for phytoremediation by reducing arsenic accumulation in the root and shoot.

Evaluation of biocontrol efficacy of rhizosphere Pseudomonas aeruginosa for management of Phytophthora capsici of pepper

A significant population of biocontrol microorganisms resides in the rhizosphere of plants, which can be utilized for plant disease control. To explore the potential of rhizosphere soil microorganisms as biocontrol agents against pepper blight, a bacterial strain Pa608 was screened from rhizosphere soil of pepper and identified as Pseudomonas aeruginosa through morphological characteristics and 16S rRNA sequences. The result showed that the strain Pa608 demonstrated antagonistic activity against Phytophthora capsici, effectively suppressing mycelial growth. The potted experiment showed a high control efficacy of 88.0%. Remarkably, the strain Pa608 also reduced the disease index of pepper blight in the field, resulting in control efficiencies of 74.9%. Moreover, the strain Pa608 also enhanced pepper plant height and yield. GC-MS analysis revealed the production of numerous secondary metabolites by the strain Pa608, with α-pinene displaying potent anti-oomycete activity by inhibiting P. capsici growth. In conclusion, P. aeruginosa Pa608 exhibited high biocontrol activity against P. capsici and can be utilized for the management of P. capsici in pepper cultivation.

Dissecting negative effects of two root-associated bacteria on the growth of an invasive weed

Plant-associated microorganisms can negatively influence plant growth, which makes them potential biocontrol agents for weeds. Two Gammaproteobacteria, Serratia plymuthica and Pseudomonas brassicacearum, isolated from roots of Jacobaea vulgaris, an invasive weed, negatively affect its root growth. We examined whether the effects of S. plymuthica and P. brassicacearum on J. vulgaris through root inoculation are concentration-dependent and investigated if these effects were mediated by metabolites in bacterial suspensions. We also tested whether the two bacteria negatively affected seed germination and seedling growth through volatile emissions. Lastly, we investigated the host specificity of these two bacteria on nine other plant species. Both bacteria significantly reduced J. vulgaris root growth after root inoculation, with S. plymuthica showing a concentration-dependent pattern in vitro. The cell-free supernatants of both bacteria did not affect J. vulgaris root growth. Both bacteria inhibited J. vulgaris seed germination and seedling growth via volatiles, displaying distinct volatile profiles. However, these negative effects were not specific to J. vulgaris. Both bacteria negatively affect J. vulgaris through root inoculation via the activity of bacterial cells, while also producing volatiles that hinder J. vulgaris germination and seedling growth. However, their negative effects extend to other plant species, limiting their potential for weed control.

High-throughput 16S rRNA gene-based amplicon sequencing reveals the functional divergence of halophilic bacterial communities in the Suaeda salsa root compartments on the eastern coast of China

The rhizosphere environment of plants, which harbors halophilic bacterial communities, faces significant challenges in coping with environmental stressors, particularly saline soil properties. This study utilizes a high-throughput 16S rRNA gene-based amplicon sequencing to investigate the variations in bacterial community dynamics in rhizosphere soil (RH), root surface soil (RS), root endophytic bacteria (PE) compartments of Suaeda salsa roots, and adjoining soils (CK) across six locations along the eastern coast of China: Nantong (NT), Yancheng (YC), Dalian (DL), Tianjin (TJ), Dongying (DY), and Qingdao (QD), all characterized by chloride-type saline soil. Variations in the physicochemical properties of the RH compartment were also evaluated. The results revealed significant changes in pH, electrical conductivity, total salt content, and ion concentrations in RH samples from different locations. Notably, the NT location exhibited the highest alkalinity and nitrogen availability. The pH variations were linked to HCO3- accumulation in S. salsa roots, while salinity stress influenced soil pH through H+ discharge. Despite salinity stress, enzymatic activities such as catalase and urease were higher in soils from various locations. The diversity and richness of bacterial communities were higher in specific locations, with Proteobacteria dominating PE samples from the DL location. Additionally, Vibrio and Marinobacter were prevalent in RH samples. Significant correlations were found between soil pH, salinity, nutrient content, and the abundance and diversity of bacterial taxa in RH samples. Bioinformatics analysis revealed the prevalence of halophilic bacteria, such as Bacillus, Halomonas, and Streptomyces, with diverse metabolic functions, including amino acid and carbohydrate metabolisms. Essential genes, such as auxin response factor (ARF) and GTPase-encoding genes, were abundant in RH samples, suggesting adaptive strategies for harsh environments. Likewise, proline/betaine transport protein genes were enriched, indicating potential bioremediation mechanisms against high salt stress. These findings provide insight into the metabolic adaptations facilitating resilience in saline ecosystems and contribute to understanding the complex interplay between soil conditions, bacterial communities, and plant adaptation.

Role of bacterial pathogens in microbial ecological networks in hydroponic plants

Plant-associated microbial communities are crucial for plant growth and health. However, assembly mechanisms of microbial communities and microbial interaction patterns remain elusive across vary degrees of pathogen-induced diseases. By using 16S rRNA high-throughput sequencing technology, we investigated the impact of wildfire disease on the microbial composition and interaction network in plant three different compartments. The results showed that pathogen infection significantly affect the phyllosphere and rhizosphere microbial community. We found that the primary sources of microbial communities in healthy and mildly infected plants were from the phyllosphere and hydroponic solution community. Mutual exchanges between phyllosphere and rhizosphere communities were observed, but microbial species migration from the leaf to the root was rarely observed in severely infected plants. Moreover, wildfire disease reduced the diversity and network complexity of plant microbial communities. Interactions among pathogenic bacterial members suggested that Caulobacter and Bosea might be crucial "pathogen antagonists" inhibiting the spread of wildfire disease. Our study provides deep insights into plant pathoecology, which is helpful for the development of novel strategies for phyllosphere disease prediction or prevention.

Harnessing bacterial endophytes for environmental resilience and agricultural sustainability

In the current era of environmental disasters and the necessity of sustainable development, bacterial endophytes have gotten attention for their role in improving agricultural productivity and ecological sustainability. This review explores the multifaceted contributions of bacterial endophytes to plant health and ecosystem sustainability. Bacterial endophytes are invaluable sources of bioactive compounds, promising breakthroughs in medicine and biotechnology. They also serve as natural biocontrol agents, reducing the need for synthetic fertilizers and fostering environmentally friendly agricultural practices. It provides eco-friendly solutions that align with the necessity of sustainability since they can improve pest management, increase crop resilience, and facilitate agricultural production. This review also underscores bacterial endophytes' contribution to promoting sustainable and green industrial productions. It also presented how incorporating these microorganisms into diverse industrial sectors can harmonize humankind with ecological stability. The potential of bacterial endophytes has been largely untapped, presenting an opportunity for pioneering advancements in sustainable industrial applications. Their importance caught attention as they provided innovative solutions to the challenging problems of the new era. This review sheds light on the remarkable potential of bacterial endophytes in various industrial sectors. Further research is imperative to discover their multifaceted potential. It will be essential to delve deeper into their mechanisms, broaden their uses, and examine their long-term impacts.

Review on biochar as a sustainable green resource for the rehabilitation of petroleum hydrocarbon-contaminated soil

Petroleum pollution is one of the primary threats to the environment and public health. Therefore, it is essential to create new strategies and enhance current ones. The process of biological reclamation, which utilizes a biological agent to eliminate harmful substances from polluted soil, has drawn much interest. Biochars are inexpensive, environmentally beneficial carbon compounds extensively employed to remove petroleum hydrocarbons from the environment. Biochar has demonstrated an excellent capability to remediate soil pollutants because of its abundant supply of the required raw materials, sustainability, affordability, high efficacy, substantial specific surface area, and desired physical-chemical surface characteristics. This paper reviews biochar's methods, effectiveness, and possible toxic effects on the natural environment, amended biochar, and their integration with other remediating materials towards sustainable remediation of petroleum-polluted soil environments. Efforts are being undertaken to enhance the effectiveness of biochar in the hydrocarbon-based rehabilitation approach by altering its characteristics. Additionally, the adsorption, biodegradability, chemical breakdown, and regenerative facets of biochar amendment and combined usage culminated in augmenting the remedial effectiveness. Lastly, several shortcomings of the prevailing methods and prospective directions were provided to overcome the constraints in tailored biochar studies for long-term performance stability and ecological sustainability towards restoring petroleum hydrocarbon adultered soil environments.

Plant Growth Promoting Rhizobacteria (PGPR) induced protection: A plant immunity perspective

Plant-environment interactions, particularly biotic stress, are increasingly essential for global food security due to crop losses in the dynamic environment. Therefore, understanding plant responses to biotic stress is vital to mitigate damage. Beneficial microorganisms and their association with plants can reduce the damage associated with plant pathogens. One such group is PGPR (Plant growth-promoting rhizobacteria), which influences plant immunity significantly by interacting with biotic stress factors and plant signalling compounds. This review explores the types, metabolism, and mechanisms of action of PGPR, including their enzyme pathways and the signalling compounds secreted by PGPR that modulate gene and protein expression during plant defence. Furthermore, the review will delve into the crosstalk between PGPR and other plant growth regulators and signalling compounds, elucidating the physiological, biochemical, and molecular insights into PGPR's impact on plants under multiple biotic stresses, including interactions with fungi, bacteria, and viruses. Overall, the review comprehensively adds to our knowledge about PGPR's role in plant immunity and its application for agricultural resilience and food security.

Superiority of native soil core microbiomes in supporting plant growth

Native core microbiomes represent a unique opportunity to support food provision and plant-based industries. Yet, these microbiomes are often neglected when developing synthetic communities (SynComs) to support plant health and growth. Here, we study the contribution of native core, native non-core and non-native microorganisms to support plant production. We construct four alternative SynComs based on the excellent growth promoting ability of individual stain and paired non-antagonistic action. One of microbiome based SynCom (SC2) shows a high niche breadth and low average variation degree in-vitro interaction. The promoting-growth effect of SC2 can be transferred to non-sterile environment, attributing to the colonization of native core microorganisms and the improvement of rhizosphere promoting-growth function including nitrogen fixation, IAA production, and dissolved phosphorus. Further, microbial fertilizer based on SC2 and composite carrier (rapeseed cake fertilizer + rice husk carbon) increase the net biomass of plant by 129%. Our results highlight the fundamental importance of native core microorganisms to boost plant production.

Shift in the soil rhizobacterial community for enhanced solubilization and bioavailability of phosphorus in the rhizosphere of Allium hookeri Thwaites, through bioaugmentation of phosphate-solubilizing bacteria

Allium hookeri is an indigenous perennial herb known for its therapeutic properties. It's grown in the eastern Himalayas and East Asia, where it is used as a flavoring agent in local cuisines. This research aims to enhance soil phosphorus mobilization and promote A. hookeri growth using a consortium of phosphate-solubilizing bacteria (PSB). The synergistic effect of a bacterial consortium containing multiple PSBs (Arthrobacter luteolus and several Klebsiella spp.) combined with tricalcium phosphate (TCP), was investigated to enhance the growth of A. hookeri plants, and its influence on modulating the rhizosphere microbiome was also assessed. The greenhouse experiment revealed that the bacterial consortium with tricalcium phosphate (BTCP) treatment enhanced the dry shoot weight by 70%. Proteobacteria dominated the rhizosphere's microbiome in all treatments. BTCP treatment enhanced the relative abundance of several beneficial genera such Bacillus, Mesorhizobium, Pseudomonas, Ensifer, Hyphomicrobium, Planctomyces, and Bradyrhizobium. The augmentation of bacterial consortium increased P in shoots (4.36 ± 0.63 mg/g) and in roots (2.34 ± 0.27 mg/g), which was more than 500% higher as compared to the uninoculated control. Canonical correspondence analysis (CCA) indicated significant correlations (p ≤ 0.05) between phosphorus content in the shoot, fresh weight, and dry weight, with higher relative abundances of Bacteroidetes, Cyanobacteria, and Fibrobacteres. Functional genes related to siderophore biosynthesis, ABC transporters, phosphatenate, and phosphinate metabolism exhibited positive modulation, indicating higher relative abundances associated with the BTCP treatment. The findings demonstrate the crucial contribution of the bacterial consortium in promoting plant development, improving soil nutrient levels, and influencing the rhizospheric microbiota, implying its significance in sustainable agriculture.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-024-04026-2.

Unlocking the potential of biofilm-forming plant growth-promoting rhizobacteria for growth and yield enhancement in wheat (Triticum aestivum L.)

Plant growth-promoting rhizobacteria (PGPR) boost crop yields and reduce environmental pressures through biofilm formation in natural climates. Recently, biofilm-based root colonization by these microorganisms has emerged as a promising strategy for agricultural enhancement. The current work aims to characterize biofilm-forming rhizobacteria for wheat growth and yield enhancement. For this, native rhizobacteria were isolated from the wheat rhizosphere and ten isolates were characterized for plant growth promoting traits and biofilm production under axenic conditions. Among these ten isolates, five were identified as potential biofilm-producing PGPR based on in vitro assays for plant growth-promoting traits. These were further evaluated under controlled and field conditions for their impact on wheat growth and yield attributes. Surface-enhanced Raman spectroscopy analysis further indicated that the biochemical composition of the biofilm produced by the selected bacterial strains includes proteins, carbohydrates, lipids, amino acids, and nucleic acids (DNA/RNA). Inoculated plants in growth chamber resulted in larger roots, shoots, and increase in fresh biomass than controls. Similarly, significant increases in plant height (13.3, 16.7%), grain yield (29.6, 17.5%), number of tillers (18.7, 34.8%), nitrogen content (58.8, 48.1%), and phosphorus content (63.0, 51.0%) in grains were observed in both pot and field trials, respectively. The two most promising biofilm-producing isolates were identified through 16 s rRNA partial gene sequencing as Brucella sp. (BF10), Lysinibacillus macroides (BF15). Moreover, leaf pigmentation and relative water contents were significantly increased in all treated plants. Taken together, our results revealed that biofilm forming PGPR can boost crop productivity by enhancing growth and physiological responses and thus aid in sustainable agriculture.

Unboxing PGPR-mediated management of abiotic stress and environmental cleanup: what lies inside?

Abiotic stresses including heavy metal toxicity, drought, salt and temperature extremes disrupt the plant growth and development and lowers crop output. Presence of environmental pollutants further causes plants suffering and restrict their ability to thrive. Overuse of chemical fertilizers to reduce the negative impact of these stresses is deteriorating the environment and induces various secondary stresses to plants. Therefore, an environmentally friendly strategy like utilizing plant growth-promoting rhizobacteria (PGPR) is a promising way to lessen the negative effects of stressors and to boost plant growth in stressful conditions. These are naturally occurring inhabitants of various environments, an essential component of the natural ecosystem and have remarkable abilities to promote plant growth. Furthermore, multifarious role of PGPR has recently been widely exploited to restore natural soil against a range of contaminants and to mitigate abiotic stress. For instance, PGPR may mitigate metal phytotoxicity by boosting metal translocation inside the plant and changing the metal bioavailability in the soil. PGPR have been also reported to mitigate other abiotic stress and to degrade environmental contaminants remarkably. Nevertheless, despite the substantial quantity of information that has been produced in the meantime, there has not been much advancement in either the knowledge of the processes behind the alleged positive benefits or in effective yield improvements by PGPR inoculation. This review focuses on addressing the progress accomplished in understanding various mechanisms behind the protective benefits of PGPR against a variety of abiotic stressors and in environmental cleanups and identifying the cause of the restricted applicability in real-world.

Potential of the plant growth-promoting rhizobacterium Rhodococcus qingshengii LMR356 in mitigating lead stress impact on Sulla spinosissima L

Mining-related lead (Pb) pollution of the soil poses serious hazards to ecosystems and living organisms, including humans. Improved heavy metal phytoremediation efficacy, achieved by using phytostabilizing plants assisted by plant-growth-promoting (PGP) microorganisms, has been presented as an effective strategy for remediating polluted soils. The objective of this research was to examine the response and potential of the plant-growth-promoting bacterium LMR356, a Rhodococcus qingshengii strain isolated from an abandoned mining soil, under lead stress conditions. Compared to non-contaminated culture media, the presence of lead induced a significant decrease in auxin production (from 21.17 to 2.65 μg mL-1) and phosphate solubilization (from 33.60 to 8.22 mg L-1), whereas other PGP traits increased drastically, such as 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity (from 38.17 to 71.37 nmol mg-1 h-1 α-ketobutyrate), siderophore production (from 69 to 83%), exopolysaccharide production (from 1952.28 to 3637.72 mg mL-1), biofilm formation, and motility. We, therefore, investigated the behavior of Sulla spinosissima L. in the presence or absence of this strain under a variety of experimental conditions. Under hydroponic conditions, Sulla plants showed endurance to varying lead concentrations (500-1000 μM). Inoculation of plants with Rhodococcus qingshengii strain LMR356 enhanced plant tolerance, as demonstrated by the increase in plant biomass (ranging from 14.41 to 79.12%) compared to non-inoculated Pb-stressed and non-stressed control plants. Antioxidant enzyme activities (increasing by -42.71 to 126.8%) and chlorophyll (383.33%) and carotenoid (613.04%) content were also augmented. In addition to its impact on plant lead tolerance, strain LMR356 showed a growth-promoting effect on Sulla plants when cultivated in sterilized non-contaminated sand. Parameters such as plant biomass (16.57%), chlorophyll (24.14%), and carotenoid (30%) contents, as well as ascorbate peroxidase (APX), peroxidase (POD), and catalase (CAT) activities, were all elevated compared to non-inoculated plants. Furthermore, when the same plant species was cultivated in highly polluted soil, inoculation increased plant biomass and improved its physiological properties. These findings demonstrate that LMR356 is a phytobeneficial bacterial strain capable of enhancing Sulla growth under normal conditions and improving its heavy metal tolerance in multi-polluted soils. Thus, it can be considered a promising biofertilizer candidate for growing Sulla spinosissima L. or other selected plants intended for application in restoration and stabilization initiatives aimed at reviving and safeguarding environmentally compromised and polluted soils after mining activities.

Production of Exopolysaccharides and İndole Acetic Acid (IAA) by Rhizobacteria and Their Potential against Drought Stress in Upland Rice

Peatlands are marginal agricultural lands due to highly acidic soil conditions and poor drainage systems. Drought stress is a big problem in peatlands as it can affect plants through poor root development, so technological innovations are needed to increase the productivity and sustainability of upland rice on peatlands. Rhizobacteria can overcome the effects of drought stress by altering root morphology, regulating stress-responsive genes, and producing exopolysaccharides and indole acetic acid (IAA). This study aimed to determine the ability of rhizobacteria in upland rice to produce exopolysaccharides and IAA, identify potential isolates using molecular markers, and prove the effect of rhizobacteria on viability and vigor index in upland rice. Rhizobacterial isolates were grown on yeast extract mannitol broth (YEMB) medium for exopolysaccharides production testing and Nutrient Broth (NB)+L-tryptophan medium for IAA production testing. The selected isolates identify using sequence 16S rRNA. The variables observed in testing the effect of rhizobacteria were germination ability, vigour index, and growth uniformity. EPS-1 isolate is the best production of exopolysaccharides (41.6 mg/ml) and IAA (60.83 ppm). The isolate EPS-1 was identified as Klebsiella variicola using 16S rRNA sequencing and phylogenetic analysis. The isolate EPS-1 can increase the viability and vigor of upland rice seeds. K. variicola is more adaptive and has several functional properties that can be developed as a potential bioagent or biofertilizer to improve soil nutrition, moisture and enhance plant growth. The use of rhizobacteria can reduce dependence on the use of synthetic materials with sustainable agriculture.