Search Results (109)

Bacterial canker, caused by Pseudomonas syringae pv. actinidiae (Psa) is a major threat to global kiwifruit production. Copper-based bactericides remain widely used, but increasing resistance highlights the urgency of developing sustainable alternatives. Understanding the functional capabilities of phyllosphere bacteria under copper pressure is critical for designing microbiome-informed management strategies. This study provides a culture-based functional inventory of bacteria associated with Actinidia chinensis var. deliciosa leaves from Portuguese orchards under long-term copper management, aiming to identify native taxa with traits relevant to plant health and resilience. A total of 1058 isolates were recovered and grouped into 261 Random Amplification of Polymorphic DNA (RAPD) clusters, representing 58 species across 29 genera. Representative strains were screened for Plant Growth-Promoting (PGP) traits (Indole-3-acetic acid (IAA), siderophore production, phosphate solubilization, ammonia production), copper tolerance, and in vitro antagonism against Psa. Copper resistance was widespread (53.3% of isolates with MIC ≥ 0.8 mM), including the first evidence of a highly copper-resistant PSA strain in Portuguese kiwifruit orchards and an exceptionally resistant non-pathogenic strain closely related to Erwinia iniecta (MIC 2.8 mM). A subset of 25 isolates combined all four PGP traits, and several also exhibited antagonism against Psa in vitro, among them Bacillus pumilus consistently supressed pathogen growth. Notably, antagonistic and multifunctional traits co-occurred in some isolates, highlighting promising candidates for integrated biocontrol strategies. Overall, the findings reveal a functionally diverse and copper-resilient collection of cultured bacteria, offering both challenges and opportunities for microbiome-based disease management. This work establishes a robust functional basis for subsequent in planta validation and the development of sustainable, microbiome-informed approaches for Psa control. Full article

Pseudomonas has been revealed as an important member of plant probiotics, with its rich species diversity implying complementary plant growth-promoting (PGP) traits. However, information on Pseudomonas species in the microecology of Angelica sinensis and medicinal plants in general remains to be further investigated. This study examined the microecological characteristics, PGP traits, and their underlying molecular mechanisms of Pseudomonas. Filling this gap will provide an important reference for microbial community design centered on dominant functional bacterial genera. In this study, we characterized the microecological traits, PGP properties, and their underlying molecular mechanisms of Pseudomonas strains. Microbiome analysis identified Pseudomonas as the dominant genus in the rhizosphere and a core endophytic genus, exerting significant influences on both (path coefficients = 0.971, 0.872). Comparative phenomics suggested potential functional complementarity among different strains. Our observations revealed significant differentiation in PGP traits: P. umsongensis X08 showed exceptional performance in IAA and siderophore production (IAA: 1.24 mg/mL, siderophore halo diameter: 2.04 cm); P. frederiksbergensis X06 exhibited advantages in ACC deaminase activity and potassium solubilization; and P. allii X32 demonstrated high organic phosphorus solubilization capability (3.98 mg/L). Finally, genomic data revealed that P. allii X32 possesses a rich repertoire of PGP-related genes and metabolic pathways, providing a basis for establishing molecular mechanistic hypotheses for these traits. In summary, Pseudomonas strains from different species, which exhibit complementary probiotic functions without antagonism in the A. sinensis microecosystem, provide valuable microbial resources for the ecological cultivation of A. sinensis. Full article

(1) Background: Oat (Avena sativa L.) is a crop that is widely used in human nutrition, while it also plays an important role in animal husbandry as a high-quality forage crop. However, this crop is particularly susceptible to combined biotic stressors, including insect pests (Agriotes lineatus) and fungal infections (Fusarium spp.). These stresses act synergistically: root damage caused by wireworms increases the plant’s susceptibility to fungal infection, while pathogens further limit nutrient uptake and root system development. In recent years, the reduced efficacy of chemical pesticides against both insect pests and fungal pathogens has highlighted the need for alternative strategies in oat protection, leading to an increased focus on developing bacterial bio-inoculants as sustainable and effective biocontrol agents. (2) Methods: This study aimed to identify bacterial strains capable of suppressing wireworms (Agriotes lineatus) and Fusarium spp. in oats, while simultaneously promoting plant growth. Bacterial isolates were screened for key Plant Growth Promoting (PGP) and biocontrol traits, including IAA and siderophore production, phosphate solubilization, and the presence of toxin- and antibiotic-coding genes. (3) Results: The highest insecticidal effect against wireworms was recorded for Bacillus velezensis BHC 3.1 (63.33%), while this isolate also suppressed the growth of F. proliferatum for 59%, F. oxysporum for 65%, F. poae for 71%, and F. graminearum for 15%. The most effective Bacillus strains (with insecticidal and antifungal activity) were identified and tested in two pot experiments, where their ability to enhance plant growth in the presence of insects and fungi was evaluated under semi-controlled conditions. An increase in plant biomass, grain yield, and nitrogen content was observed in oat inoculated with B. velezensis BHC 3.1 and B. thuringiensis BHC 2.4. (4) Conclusions: These results demonstrate the strong potential of both strains as multifunctional bio-inoculants for enhancing oat growth and mitigating the adverse effects of wireworm damage and Fusarium infection. Full article

Background Soil alkalization inhibits plant growth and yield, the endophytic plant growth-promoting bacteria (PGPB) can alleviate salt stresses for plant. Methods: Isolate a NaHCO₃-tolerant Bacillus amyloliquefaciens strain (ZmBA DSM7), characterize its PGP traits, elucidate the physiological and biochemical mechanisms by which it enhances maize growth. Results: A ZmBA DSM7 strain was isolated from the root of maize growing in a mildly alkaline soil (pH 8.8). The strain exhibited high tolerance to 500 mM NaHCO₃ and maintained its PGP traits, ZmBA DSM7 had a positive effect on maize seed germination and alkaline stress tolerance by enhancing seed vigor under normal or alkaline growth conditions. The maize seedlings inoculation with ZmBA DSM7 markedly improved chlorophyll content and reduced oxidative damage by lowering malondialdehyde (MDA) content and enhancing the antioxidant enzymes activities in the pots. In the field, ZmBA DSM7-inoculated plants showed a increase in yield (such as the ear length, the number of kernels row number, average spike weight, the 100-grain weight, and so on). Conclusion: The ZmBA DSM7 promotes maize growth and mitigates NaHCO₃-induced alkaline stress in maize by a multifaceted mechanism involving enhanced nutrient acquisition (N, P and K) and antioxidant status and improved soil quality. Full article

The presence of substantial amounts of heavy metals in the environment can result in various significant ecological issues and human health risks. Currently, bioremediation employing microorganisms is garnering significant interest due to its effectiveness. The present investigation aimed to isolate actinobacterial strains from an Italian mine and to characterise them for heavy metals resistance and plant growth-promoting characteristics. The different samples were processed for DNA extraction and 16S rRNA gene metabarcoding to investigate the bacteria and archaea communities. Cultivable microbiota were isolated and evaluated for heavy metals tolerance and different PGP traits. The most pertinent strains were tested for compatibility, merged into a consortium, and tested on Lemna minor L. Metabarcoding analysis revealed that amplicon sequence variants (ASVs) at the phylum level were mostly assigned to proteobacteria and bacteroidota. Uncultured and unknown taxa were the most prevalent in the samples at the genus level. A total of ten strains were obtained from the culture-dependent approach exhibiting interesting heavy metals tolerance and plant growth-promoting traits. The best strains (MTW 1 and MTW 5) were selected and further characterised by 16S barcoding. These strains were identified as Streptomyces atratus (99.57% identity). An in planta experiment showed that the metal-tolerant consortium MTW 1-5 improved plant physiology by significantly optimising plant growth and tolerance to heavy metals. The experiment conducted provided evidence for the possibility of using actinobacteria as bioaugmentation agents to improve the phytoextraction abilities of L. minor. Full article

Duckweeds are small, fast-growing aquatic plants with high starch and protein content, making them promising candidates for next-generation plant biomass resources. Despite their importance, little is known about their interactions with microorganisms, particularly plant growth-promoting bacteria (PGPB), which play key roles in enhancing plant productivity. In this study, we report the plant growth-promoting effects of strain LA-C6, a member of the phylum Armatimonadota, isolated from duckweed fronds. Based on 16S rRNA gene analysis, this strain represents a novel genus-level lineage, and is referred to as Fimbriimonadaceae bacterium strain LA-C6. In axenic co-culture experiments, strain LA-C6 promoted duckweed growth, increasing the frond proliferation of four duckweed species (Lemna minor, Lemna aequinoctialis, Spirodela polyrhiza, and Landoltia punctata) by 1.8- to 4.0-fold compared with uninoculated controls. Importantly, three other phylogenetically distinct Armatimonadota species also exhibited significant plant growth-promoting effects on L. minor, increasing frond number by up to 2.3-fold and dry weight by up to 2.4-fold. This finding highlights the broader potential of diverse Armatimonadota members as PGP bacteria. A survey of the IMNGS database showed that strain LA-C6 and other Armatimonadota species are widely distributed across diverse plant-associated environments. Biochemical assays and gene prediction analyses revealed that strain LA-C6 produces indole-3-acetic acid (IAA) as a representative PGP trait, whereas no additional PGP-associated traits were detected. These results suggest that diverse bacterial lineages within the phylum Armatimonadota exert growth-promoting effects on aquatic plants, potentially through yet-to-be-identified mechanisms. Full article

Plant growth-promoting bacteria (PGPBs) offer a sustainable alternative for enhancing crop productivity in low-fertility tropical soils. In this study, 30 bacterial isolates were screened in vitro for multiple PGP traits, including phosphate solubilization (from aluminum phosphate—AlPO₄ and thermophosphate), potassium release from phonolite rock, siderophore production, indole-3-acetic acid (IAA) synthesis, ACC deaminase activity, and antagonism against Fusarium spp. Statistical analysis revealed significant differences (p < 0.05) among the isolates. The most efficient isolates demonstrated a solubilization capacity ranging from 24.0 to 45.2 mg L⁻¹ for thermophosphate and 21.7 to 23.5 mg L⁻¹ for potassium from phonolite. Among them, Pseudomonas azotoformans K22 showed the highest AlPO₄ solubilization (16.6 mg L⁻¹). IAA production among the isolates varied widely, from 1.34 to 9.65 µg mL⁻¹. Furthermore, 17 isolates produced carboxylate-type siderophores, and only Pseudomonas aeruginosa SS183 exhibited ACC deaminase activity, coupled with strong antifungal activity (91% inhibition). A composite performance index identified P. azotoformans K22, E. hormaechei SS150, S. sciuri SS120, and B. cereus SS18 and SS17 as the most promising isolates. This study provides a valuable foundation for characterizing plant growth-promoting traits and identifies key candidates for future validation and the development of microbial consortia. Full article

This study investigated the isolation and formulation of a bacterial conditioner as a biostimulant for Triticum durum (durum wheat) under salinity stress. An Algerian alkaline–saline soil was sampled, characterized for its physical and chemical characteristics and its culturable and total microbial community (16S rRNA gene metabarcoding). Three bacterial strains showing high 16S rRNA gene similarity to Pseudomonas putida, Bacillus proteolyticus, and Niallia nealsonii were selected for their plant growth-promoting (PGP) traits under different salinity levels, including phosphate solubilisation (194 µg mL⁻¹), hormone production (e.g., gibberellin up to 56 µg mL⁻¹), and good levels of hydrocyanic acid, ammonia, and siderophores. N. nealsonii maintained high indole production under saline conditions, while B. proteolyticus displayed enhanced indole synthesis at higher salt concentrations. Siderophore production remained stable for P. putida and N. nealsonii, whereas for B. proteolyticus a complete inhibition was registered in the presence of salt stress. The consortium density and application were tested under controlled conditions using Medicago sativa as a model plant. The effective biostimulant formulation was tested on Triticum durum under greenhouse experiments. Bacterial inoculation significantly improved plant growth in the presence of salt stress. Root length increased by 91% at 250 mM NaCl. Shoot length was enhanced by 112% at 500 mM NaCl. Total chlorophyll content increased by 208% at 250 mM NaCl. The chlorophyll a/b ratio increased by 117% at 500 mM. Also, reduced amounts of plant extracts were necessary to scavenge 50% of radicals (−22% at 250 mM compared to the 0 mM control). Proline content increased by 20% at both 250 mM and 500 mM NaCl. These results demonstrate the potential of beneficial bacteria as biostimulants to mitigate salt stress and enhance plant yield in saline soils. Full article

The undefined microbial ecology of Aconitum carmichaelii root rot in western Yunnan constrains the advancement of eco-friendly control strategies. The identification of potential pathogenic determinants affecting A. carmichaelii growth is imperative for sustainable cultivation and ecosystem integrity. High-throughput sequencing was employed to profile microbial communities across four critical niches, namely rhizosphere soil, tuberous root epidermis, root endosphere, and fibrous roots of healthy and diseased A. carmichaelii. The physicochemical properties of corresponding rhizosphere soils were concurrently analyzed. Putative pathogens were isolated from diseased rhizospheres and tubers through culturing with Koch’s postulates validation, while beneficial microorganisms exhibiting antagonism against pathogens and plant growth-promoting (PGP) traits were isolated from healthy rhizospheres. Highly virulent strains (2F14, FZ1, L23) and their consortia were targeted for suppression. Strain DX3, demonstrating optimal PGP and antagonistic capacity in vitro, was selected for pot trials evaluating growth enhancement and disease control efficacy. Significant disparities in rhizosphere soil properties and bacterial/fungal community structures were evident between healthy and diseased cohorts. Fifteen putative pathogens spanning eight species across four genera were isolated: Fusarium solani, F. avenaceum, Clonostachys rosea, Mucor racemosus, M. irregularis, M. hiemalis, Serratia liquefaciens, and S. marcescens. Concurrently, eight PGP biocontrol strains were identified: Bacillus amyloliquefaciens, B. velezensis, B. subtilis, B. pumilus, and Paenibacillus polymyxa. Pot trials revealed that Bacillus spp. enhanced soil physiochemical properties through nitrogen fixation, phosphate solubilization, potassium mobilization, siderophore production, and cellulose degradation, significantly promoting plant growth. Critically, DX3 inoculation elevated defense-related enzyme activities in A. carmichaelii, enhanced host resistance to root rot, and achieved >50% disease suppression efficacy. This work delineates key pathogenic determinants of Yunnan A. carmichaelii root rot and identifies promising multifunctional microbial resources with dual PGP and biocontrol attributes. Our findings provide novel insights into rhizosphere microbiome-mediated plant health and establish a paradigm for sustainable disease management. Full article

Plant growth-promoting rhizobacteria (PGPR) employ various mechanisms to enhance plant development and growth as well as to mitigate environmental stress, including heavy metal contamination. Cadmium is a particularly severe stressor, toxic to both plants and soil microbiota. Mesembryanthemum crystallinum L. (the common ice plant), a fast-growing semi-halophyte, was previously investigated for phytoremediation potential towards saline environments and toxic metals, especially cadmium and chromium. The study was aimed at assessing whether bacteria isolated from the rhizosphere of M. crystallinum treated with Cd reveal growth-promoting traits and if the plant tolerance to Cd results from a synergistic action of the Cd/salt-resistant strains. The isolates demonstrated PGP characteristics, including nitrogen fixation, phosphate solubilization, and production of ammonia, indolyl-3-acetic acid (IAA), and siderophores. A microbial consortium consisting of these strains was developed and applied to pots with M. crystallinum. After a 14-day experiment, plant growth and Cd-accumulation potential were evaluated upon treatment with 1 mM or 10 mM Cd, either in the presence or absence of NaCl. Plant inoculation with the consortium stimulated Cd accumulation both by roots and shoots at 10 mM Cd under saline conditions. The results suggest that bioaugmentation of M. crystallinum with the bacterial community can be used as an effective, sustainable phytoremediation method for cadmium-contaminated soils. Full article

Exploring microbial resources from coastal environments is crucial for enhancing food security; however, current knowledge remains limited. This study aimed to isolate and molecularly characterize bacteria associated with maize and groundnut, and to evaluate their potential as plant growth-promoting (PGP) agents. Rhizobacteria were isolated from rhizospheric soil, and endophytic bacteria were obtained from surface-sterilized and macerated plant roots. One gram of each sample was suspended in sterile distilled water in test tubes, serially diluted, and plated on nutrient agar. After incubation, distinct colonies were sub-cultured to obtain pure cultures for biochemical tests, screening for PGP traits, assessment of pH and salt tolerance, optimal growth conditions, bioinoculation potential, and molecular analysis. Out of sixty isolated bacteria, five potent strains, BS1-BS5, were identified. BS3 showed the highest mannanase activity, with a 2.3 cm zone of clearance, while BS2 exhibited high indole-3-acetic acid (IAA) and phosphate solubilization activities of 10.92 µg/mL and 10.78 mg/L. BS1 and BS4 demonstrated high drought tolerance, 0.94 and 0.98 at 10% PEG, with BS1 also showing maximum salt tolerance of 0.76. At 6.0 g and 2.0 g supplementation, BS1 and BS2 utilized 100% lactose and fructose. BS3 exhibited the highest percentage of antifungal activity, with a 30.12% inhibition rate. BS4 and BS5 promoted shoot lengths of 55.00 cm and 49.80 cm, respectively. Although the bacterial species isolated are generally considered pathogenic, their positive effects contributed significantly to maize growth. Full article

A diverse array of soil microorganisms exhibit plant growth-promoting (PGP) traits, many of which enhance root growth and development. These microorganisms include various taxa of bacteria, fungi, microalgae and yeasts—some of which are currently used in biofertilizers and biostimulant formulations. Recent studies have begun to unravel the complex communication between plant roots and beneficial microorganisms, revealing mechanisms that modulate root nitrogen (N) uptake beyond atmospheric N₂ fixation pathways. Root N uptake is tightly regulated by plants through multiple mechanisms. These include transcriptional and post-transcriptional control of plasma membrane-localized N transporters in the epidermis, endodermis, and xylem parenchyma. Additionally, N uptake efficiency is influenced by vacuolar N storage, assimilation of inorganic N into organic compounds, and the maintenance of electrochemical gradients across root cell membranes. Many of these processes are modulated by microbial signals. This review synthesizes current knowledge on how soil microorganisms influence root N uptake, with a focus on signaling molecules released by soil beneficial microbes. These signals include phytohormones, volatile organic compounds (VOCs), and various low-molecular-weight organic compounds that affect transporter expression, root architecture, and cellular homeostasis. Special attention is paid to the molecular and physiological pathways through which these microbial signals enhance plant N acquisition and overall nutrient use efficiency. Full article

Climate change has intensified extreme weather events and accelerated soil salinization, posing serious threats to crop yield and quality. Salinity stress, now affecting about 20% of irrigated lands, is expected to worsen due to rising temperatures and sea levels. At the same time, the global population is projected to exceed 9 billion by 2050, demanding a 70% increase in food production (UN, 2019; FAO). Agriculture, responsible for 34% of global greenhouse gas emissions, urgently needs sustainable solutions. Microbial inoculants, known as “plant probiotics,” offer a promising eco-friendly alternative by enhancing crop resilience and reducing environmental impact. In this study, we evaluated the plant growth-promoting (PGP) traits and melatonin-producing capacity of Bacillus aerius EH2-5. To assess its efficacy under salt stress, soybean seedlings at the VC stage were inoculated with EH2-5 and subsequently subjected to salinity stress using 150 mM and 100 mM NaCl treatments. Plant growth parameters, the expression levels of salinity-related genes, and the activities of antioxidant enzymes were measured to determine the microbe’s role in promoting plant growth and mitigating salt-induced oxidative stress. Here, our study shows that the melatonin-synthesizing Bacillus aerius EH2-5 (7.48 ng/mL at 24 h after inoculation in Trp spiked LB media) significantly improved host plant (Glycine max L.) growth, biomass, and photosynthesis and reduced oxidative stress during salinity stress conditions than the non-inculcated control. Whole genome sequencing of Bacillus aerius EH2-5 identified key plant growth-promoting and salinity stress-related genes, including znuA, znuB, znuC, and zur (zinc uptake); ptsN, aspA, and nrgB (nitrogen metabolism); and phoH and pstS (phosphate transport). Genes involved in tryptophan biosynthesis and transport, such as trpA, trpB, trpP, and tspO, along with siderophore-related genes yusV, yfhA, and yfiY, were also detected. The presence of multiple stress-responsive genes, including dnaK, dps, treA, cspB, srkA, and copZ, suggests EH2-5′s genomic potential to enhance plant tolerance to salinity and other abiotic stresses. Inoculation with Bacillus aerius EH2-5 significantly enhanced soybean growth and reduced salt-induced damage, as evidenced by increased shoot biomass (29%, 41%), leaf numbers (12% and 13%), and chlorophyll content (40%, 21%) under 100 mM and 150 mM NaCl compared to non-inoculated plants. These results indicate EH2-5′s strong potential as a plant growth-promoting and salinity stress-alleviating rhizobacterium. The EH2-5 symbiosis significantly enhanced a key ABA biosynthesis enzyme-related gene NCED3, dehydration responsive transcription factors DREB2A and NAC29 salinity stresses (100 mM and 150 mM). Moreover, the reduced expression of peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) by 16%, 29%, and 24%, respectively, and decreased levels of malondialdehyde (MDA) and hydroxy peroxidase (H₂O₂) by 12% and 23% were observed under 100 mM NaCl compared to non-inoculated plants. This study demonstrated that Bacillus aerius EH2-5, a melatonin-producing strain, not only functions effectively as a biofertilizer but also alleviates plant stress in a manner comparable to the application of exogenous melatonin. These findings highlight the potential of utilizing melatonin-producing microbes as a viable alternative to chemical treatments. Therefore, further research should focus on enhancing the melatonin biosynthetic capacity of EH2-5, improving its colonization efficiency in plants, and developing synergistic microbial consortia (SynComs) with melatonin-producing capabilities. Such efforts will contribute to the development and field application of EH2-5 as a promising plant biostimulant for sustainable agriculture. Full article

Sustainable agriculture requires replacing agrochemicals with environmentally friendly products. One alternative is bacterial inoculants with plant-growth-promoting (PGP) activity. Bacterial consortia offer advantages over single-strain inoculants, as they possess more PGP traits and allow the exploitation of bacterial synergies. Synthetic bacterial communities (SynComs) can be used as inoculants that are thoroughly characterized and assessed for efficiency and safety. Here, we describe the construction of a SynCom composed of seven bacterial strains isolated from the rhizosphere of tomato plants and other orchard vegetables. The strains were identified by 16S rDNA sequencing as Pseudomonas spp. (two isolates), Rhizobium sp., Ensifer sp., Microbacterium sp., Agromyces sp., and Chryseobacterium sp. The metagenome of the combined strains was sequenced, allowing the identification of PGP traits and the assembly of their individual genomes. These traits included nutrient mobilization, phytostimulation, and biocontrol. When inoculated into tomato plants in an agricultural soil, the SynCom caused minor effects in soil and rhizosphere bacterial communities. However, it had a high impact on the gene expression pattern of tomato plants. These effects were more significant at the systemic than at the local level, indicating a priming effect in the plant, as signaling through jasmonic acid and ethylene appeared to be altered. Full article

The nursery phase is vital for forest regeneration, yet studies on plant growth-promoting (PGP) bacteria to enhance sustainable nursery production in forest species are scarce. This study explores whether endophytic bacteria from disease-resistant Pinus pinea L. can improve germination and seedling quality in susceptible Pinus radiata D. Don. Root endophytes were isolated, screened for PGP traits, and identified via 16S rRNA gene sequencing. Bacterial formulations were applied to P. radiata seeds to determine their impact on germination and plant quality indicators (photosynthetic pigments and other metabolites). Paenibacillaceae (19%) and Bacillaceae (13%) were predominant among 68 isolates, with 94% producing indole-3-acetic acid, and Burkholderiaceae showing the broadest PGP trait diversity. Seedlings inoculated with formulation C3 (Caballeronia R.M3R3, Rhodococcus T.M4R4, and Mesorhizobium R.M1R2) displayed an improved germination rate (89% compared to 71% from the uninoculated control), while those inoculated with formulation P4 (Paenibacillus T.M5R4, Bacillus R.M2R7, Acinetobacter T.M2R22, and Paraburkholderia R.M1R3) showed an improved germination rate (81%), increased amount of starch (0.4-fold), and free amino acids (1.5-fold). This study presents a comprehensive approach, from endophyte isolation to in vivo tests, highlighting two bacterial formulations as candidates for further proof-of-concept nursery trials. Ultimately, these bioinoculants represent eco-friendly strategies to enhance forest seedling establishment and support sustainable forest management. Full article