Plant Growth-promoting Activities Research Articles

Mangrove sediments-associated bacterium (Bacillus sp. SW7) with multiple plant growth-promoting traits promotes the growth of tomato (Solanum Lycopersicum)

Global food production intensification presents a major hurdle to ensuring food security amidst a growing world population. Widespread use of chemical fertilizers in recent decades has risked soil fertility, compounded by the challenges posed by climate change, particularly in arid regions. To address these issues, adopting plant growth-promoting (PGP) bacteria stands out as a promising solution, offering multifaceted benefits to arid agroecosystems. We isolated a bacterial strain, SW7, from mangrove sediment, characterised the entire genome followed by phylogenetic analyses, and evaluated its in-vitro PGP activity. Subsequently, we examined its impact on tomato seed germination and plant growth. The strain SW7 exhibited growth on 11% NaCl, survival at 50°C, and possessed multiple PGP traits such as significant increase in seed germination rate (60.60 ± 38.85%), phosphate (83.3 g L−1) and potassium (39.6 g L−1) solubilization and produced indole acetic acid (3.60 ppm). Additionally, strain SW7 tested positive for ammonia, catalase, and oxidase enzyme production. The strain SW7 genome consists of 5.1 MB with 35.18% G+C content. Through genome-based phylogenetic and orthoANI analyses, the strain was identified as a novel Bacillus species, designated herein as Bacillus sp. SW7. In an eight-week shade-house experiment, inoculation of strain SW7 improved, leaf number, leaf density, leaf area index and mass water of tomatoes. Additional parameters, like chlorophyll a, chlorophyll b and carotenoids were not affected in SW7-inoculated tomatoes. In conclusion, Bacillus sp. SW7 exhibits multiple PGP traits and an adaptive capacity to high temperature and salinity, positioning it as a potential candidate for elevating the productivity of arid agroecosystems.

Unveiling the efficacy of a bacterial antagonist in the management of tomato wilt disease caused by Ralstonia solanacearum

The long-term application of agrochemicals, including pesticides, in intensive agricultural practices to protect crops from biotic stresses results in the emergence of resistance among phytopathogens and the ineffectiveness of chemical applications. The microbiological strategies, in contrast, minimize the reliance on chemicals and, hence, reduce environmental and human health risks. Bacterial wilt of tomato induced by Ralstonia solanacearum is one of the most destructive diseases worldwide that requires urgent attention to develop a safer and more efficient method to control the phytopathogen. The present work was conducted in the year 2022-2023. In this study, the bacterial wilt was managed by an antagonist bacterium, Pseudomonas fluorescens, exhibiting variable morphological, biochemical, and plant growth-promoting activities. The P. fluorescens inhibited the growth of R. solanacearum in plate assay at different time intervals (0-48 h). The SEM image of R. solanacearum cells cultured with P. fluorescens revealed pores, distortion, and fragmented cell envelope, while the untreated bacterial cells were uniform and smooth. Tomato plants infected with R. solanacearum showed 89% disease incidence compared to uninfected but PGPR-inoculated tomato plants. Application of P. fluorescens reduced disease incidence by 63% compared to R. solanacearum infested plants. Furthermore, plant length enhanced by 21 and 26% significantly following bacterial inoculation after three and four weeks of growth. Conclusively, this study emphasizes the effectiveness of using PGPR as a potent strategy for managing wilt disease in vegetable crops, especially tomato.

Biosurfactant production by Bacillus amyloliquefaciens, characterization and its potential applications

Aim: To identify indigenous bacteria responsible for producing biosurfactants in soil contaminated by oil and to investigate their potential uses in the fields of pharmaceuticals and environmental applications. Methodology: The microorganisms of oil-contaminated soil were isolated, screened, and identified using 16S rRNA gene sequencing. Bacillus amyloliquefaciens was utilized to produce biosurfactants, and were characterized by UV, TLC, FTIR, HPTLC, and GCMS analysis. Antibacterial activity, plant growth promotion, biocompatibility, and wound healing activity of surfactant were performed. Results: Six bacterial cultures (B1 to B6) were isolated from the soil samples collected from various locations in Kerala and Tamil Nadu. Among the isolates screened for biosurfactant production, Bacillus amyloliquefaciens exhibited the highest capacity for biosurfactant production, confirmed through 16S rRNA gene sequencing. The biosurfactant produced was identified as surfactin of lipopeptide nature, characterized by various analytical techniques: UV absorption at 400 nm, TLC and HPTLC (Rf value of 0.58), FTIR (prominent peak at 3819 cm-1 corresponding to -OH groups), GCMS with a maximum retention time of 12.03. Surfactin effectively inhibited pathogenic bacteria, enhanced plant growth, was biocompatible, and enhanced the rate of cell migration towards wound scratch. Interpretation: The current study revealed that Bacillus amyloliquefaciens, isolated from oil-contaminated soil, is capable of producing biosurfactant surfactin. Additionally, it unveiled a broad spectrum of applications for surfactin, encompassing wound healing, biocompatibility, antimicrobial activity, and promotion of plant growth. Key words: Antibacterial activity, Biocompatibility, Bacillus amyloliquefaciens, Biosurfactant, Wound healing

Revealing the diversity of Jojoba-associated fungi using amplicon metagenome approach and assessing the in vitro biocontrol activity of its cultivable community.

Jojoba shrubs are wild plants cultivated in arid and semiarid lands and characterized by tolerance to drought, salinity, and high temperatures. Fungi associated with such plants may be attributed to the tolerance of host plants against biotic stress in addition to the promotion of plant growth. Previous studies showed the importance of jojoba as jojoba oil in the agricultural field; however, no prior study discussed the role of jojoba-associated fungi (JAF) in reflecting plant health and the possibility of using JAF in biocontrol. Here, the culture-independent and culture-dependent approaches were performed to study the diversity of the jojoba-associated fungi. Then, the cultivable fungi were evaluated for in-vitro antagonistic activity and in vitro plant growth promotion assays. The metagenome analysis revealed the existence of four fungal phyla: Ascomycota, Aphelidiomycota, Basidiomycota, and Mortierellomycota. The phylum Ascomycota was the most common and had the highest relative abundance in soil, root, branch, and fruit samples (59.7%, 50.7%, 49.8%, and 52.4%, respectively). Alternaria was the most abundant genus in aboveground tissues: branch (43.7%) and fruit (32.1%), while the genus Discosia had the highest abundance in the underground samples: soil (24%) and root (30.7%). For the culture-dependent method, a total of 14 fungi were isolated, identified, and screened for their chitinolytic and antagonist activity against three phytopathogenic fungi (Fusarium oxysporum, Alternaria alternata and Rhizoctonia solani) as well as their in vitro plant growth promotion (PGP) activity. Based on ITS sequence analysis, the selected potent isolates were identified as AspergillusstellatusEJ-JFF3, Aspergillusflavus EJ-JFF4, Stilbocreasp. EJ-JLF1, Fusariumsolani EJ-JRF3, and AmesiaatrobrunneaEJ-JSF4. The endophyte strain A. flavus EJ-JFF4 exhibited the highest chitinolytic activity (9 Enzyme Index) and antagonistic potential against Fusarium oxysporum, Alternaria alternata, and Rhizoctonia solani phytopathogens with inhibitory percentages of 72, 70, and 80 respectively. Also, A. flavus EJ-JFF4 had significant multiple PGP properties, including siderophore production (69.3%), phosphate solubilization (95.4 µg ml-1). The greatest production of Indol-3-Acetic Acid was belonged to A.atrobrunnea EJ-JSF4 (114.5 µg ml-1). The analysis of FUNGuild revealed the abundance of symbiotrophs over other trophic modes, and the guild of endophytes was commonly assigned in all samples. For the first time, this study uncovered fungal diversity associated with jojoba plants using a culture-independent approach and in-vitro assessed the roles of cultivable fungal strains in promoting plant growth and biocontrol. The present study indicated the significance of jojoba shrubs as a potential source of diverse fungi with high biocontrol and PGP activities.

Evaluation of commercial importance of endophytes isolated from Argemone mexicana and Papaver rhoeas.

The paper industry is a composite one constituting different types of mills, processes, and products. The paper industries consume large amounts of resources, like wood and water. These industries also create huge amounts of waste that have to be treated. In our study, 23 endophytic bacteria were isolated from Argemone mexicana, and 16 endophytic bacteria were isolated from Papaver rhoeas. Seventeen and 15 bacterial endophytes from A. mexicana and P. rhoeas, respectively, showed cellulose-degrading activity. The biochemical and molecular characterization were done for endophytic bacteria with cellulolytic activity. The consortium of cellulose-degrading endophytic bacteria from A. mexicana showed endoglucanase activity (0.462IU/ml) and FPCase enzyme activity (0.269IU/ml) and from P. rhoeas gave endoglucanase activity (0.439IU/ml) and FPCase enzyme activity (0.253IU/ml). Degraded carboxy methylcellulose and filter paper were further treated by Saccharomyces cerevisiae and bioethanol was produced. Cellulose-degrading endophytic bacteria were also tested for auxin, siderophore production, and phosphate solubilization activities. Individual cellulose-degrading endophytic bacteria with plant growth-promoting activities were used as biofertilizers, tested for plant growth-promoting activities using Basmati Pusa 1121 rice, and plant growth parameters were recorded. The degraded paper enhances the growth of rice plants. Selected bacterial endophytes and their consortia from A. mexicana and P. rhoeas were powerful cellulose degraders, which can be further employed for ethanol production and as significant biofertilizers in agriculture.

Identification and genomic insights into a strain of Bacillus velezensis with phytopathogen-inhibiting and plant growth-promoting properties

The use of biological agents offers a sustainable alternative to chemical control in managing plant diseases. In this study, Bacillus velezensis IFST-221 was isolated from the rhizosphere of a healthy maize plant amidst a population showing severe disease symptoms. The investigation demonstrated a broad-spectrum antagonistic activity of IFST-221 against eight species of pathogenic ascomycetes and oomycetes, suggesting its potential utility in combating plant diseases like maize ear rot and cotton Verticillium wilt. Additionally, our study unveiled that IFST-221 has demonstrated significant plant growth-promoting properties, particularly in maize, cotton, tomato, and broccoli seedlings. This growth promotion was linked to its ability to produce indole-3-acetic acid, nitrogen fixation, phosphate and potassium solubilization, and biofilm formation in laboratory conditions. A complete genome sequencing of IFST-221 yielded a genome size of 3.858 M bp and a GC content of 46.71%. The genome analysis identified 3659 protein-coding genes, among which were nine secondary metabolite clusters with known antimicrobial properties. Additionally, three unknown compounds with potentially novel properties were also predicted from the genomic data. Genome mining also identified several key genes associated with plant growth regulation, colonization, and biofilm formation. These findings provide a compelling case for the application of B. velezensis IFST-221 in agricultural practices. The isolate’s combined capabilities of plant growth promotion and antagonistic activity against common plant pathogens suggest its promise as an integrated biological agent in disease management and plant productivity enhancement.

Abiotic stress tolerance and antifungal activities of rhizobacteria for the management of soil-borne pathogens

Cotton production is negatively affected by both biotic (diseases and insects) and abiotic (high temperature, salinity, water deficit, and extreme pH) factors. Soil-borne diseases, especially wilts and rots, significantly reduce cotton yield. Thus, we aimed to isolate and identify multi-stress tolerant bacterial antagonistic agents (AGAs) against two major soil-borne pathogens, Macrophomina phaseolina and Fusarium oxysporum. A total of 132 isolates with distinct morphologies were recovered from 25 different rhizospheric soil samples of cotton. A dual culture plate and broth assay confirmed the antagonistic activity of the isolates against these phytopathogens. Four selected AGAs thrived in salt stress induced by different NaCl concentrations, up to 1.71 M, except for isolate 62, which survived up to 0.85 M. Under osmotic stress, all the AGAs were tolerant of up to −1.03 MPa. Similarly, all the AGAs were able to survive over a temperature range of 20 to 50 °C except for isolate 62, which survived up to 45 °C and was regarded as thermotolerant. All four AGAs were able to grow at pH values ranging from 5 to 9. AGA 18 and S46-7 survived under highly acidic conditions (pH 4). These multi-stress tolerant AGAs also exhibited different plant growth-promoting activities, such as mineral solubilization, ACC-deaminase production, and IAA production. Molecular identification revealed the following AGAs: Bacillus siamensis SSVP1 (18), Bacillus halotolerans SSVP2 (34), Pseudomonas aeruginosa SSVP3 (62), and Bacillus tequilensis SSVP4 (S46-7). AGAs with multiple stress tolerance traits can serve as potential biocontrol agents in the field to reduce pesticide consumption in cotton-growing areas.

Understanding the Molecular Mechanism of PGPR Strain Priestia megaterium from Tea Rhizosphere for Stress Alleviation and Crop Growth Enhancement

The study aimed to assess the plant growth-promoting (PGP) capabilities and abiotic stress tolerance of strain IHB B 7164 with a focus on identifying associated genes through genomic analysis. Isolated from the tea rhizosphere, strain underwent screening for multiple PGP traits and stress tolerance against various abiotic factors. Taxonogenomic analysis of the complete genome identified the bacterium as Priestia megaterium exhibiting high similarity (97.04 % ANI, 74.3 % in silico DDH) to P. megaterium ATCC 14581. Functional annotations of the genome highlighted gene clusters associated with PGP traits and stress tolerance substantiating the strain's potential in promoting plant growth under stress conditions. The strain demonstarted robust growth and PGP activities under stressed culture conditions such as acidity, temperature fluctuations, desiccation, salinity, and exposure to calcium, aluminum, and iron salts, affirming its status as a stress-tolerant rhizobacterium. Screening of PGP traits under acidic conditions revealed phosphate solubilization, ACC-deaminase activity and production of IAA-like auxins. Notably gluconic and oxalic acids were consistently detected during solubilization of tri-calcium phosphate (TCP), aluminum phosphate (Al-P), and iron phosphate (Fe-P). Inoculation with the strain led to significant enhancements in tea nursery plants including a 9 % increase in plant height, 10 % increase in leaf number, and substantial improvements in leaf fresh and dry weights. Similarly, pea and wheat yields recorded notable increases of 16.9 % and 18.3 %, respectively under field conditions. These findings underscore the efficacy of P. megaterium strain IHB B 7164 as an abiotic stress-tolerant and broad-spectrum plant growth promoting rhizobacteria (PGPR) capable of enhancing plant growth and productivity across diverse agricultural settings.

Simultaneously enhancing plant growth and immunity through the application of engineered Bacillus subtilis expressing a microbial pattern1

Simultaneously enhancing plant growth and disease resistance is an ideal goal in Agriculture. Significant efforts have been made to promote plant growth or immunity through the use of biological reagents, such as the application of beneficial microbes and plant immunity inducers. However, balancing plant immunity and growth remains a challenging task. In this study, we engineered the plant growth-promoting bacterium Bacillus subtilis OKB105 to express a secreted microbial pattern, flg22, and accessed its activity in enhancing both plant growth and disease resistance. The OKB105 (flg22) strain exhibited plant growth-promoting activity similar to the OKB105 strain containing an empty vector, OKB105 (EV). Furthermore, the OKB105 (flg22) strain significantly enhanced plant resistance against two distinct pathogens, Pseudomonas syringae DC3000 ΔhopQ1-1 and Phytophthora parasitica, compared to OKB105 (EV), confirming that the engineered OKB105 (flg22) effectively enhances plant disease resistance. Interestingly, root irrigation with OKB105 (flg22) also markedly boosted the plant’s aboveground resistance to pathogens compared to OKB105 (EV). We further demonstrated that OKB105 (flg22) can be applied to confer resistance to pathogens in other plants that recognize flg22. Finally, RNA-Seq and qRT-PCR analyses illustrated that OKB105 (flg22) effectively induced the expression of defense-related genes in pattern-triggered immunity. Our results prove that employing an engineered beneficial microbe expressing a microbial pattern is a promising strategy for simultaneously enhancing plant growth and immunity.

Bacillus thuringiensis promotes systemic immunity in tomato, controlling pests and pathogens and promoting yield

AbstractPlant pathogens and pests pose an increasing threat to worldwide food security. To improve and strengthen food security under increasingly difficult environmental, economic, and geopolitical conditions, the prospect of using microbial biocontrol agents becomes increasingly desirable. One of the most studied, and commercially used, biopesticide microorganisms is the entomopathogenic, gram-positive, soil bacterium Bacillus thuringiensis (Bt). While Bt has been known for many years as an insecticidal microorganism and used extensively in agriculture, its possible anti-phytopathogen and plant growth-promoting activities have received comparatively limited attention thus far. Here, we examine the ability of Bt to promote systemic immunity in tomato plants. We investigate how Bt influences plant immunity and disease resistance against several fungal and bacterial plant pathogens, as well as several arthropod pests. In order to determine which component of Bt (i.e., Bt spores or pure crystals) is responsible for the observed effects on pathogens or pests, we dissected the different fractions present in a commercial preparation and assessed their effects on pest and pathogen control. As previously reported in the Bt literature, our results indicate that proteins produced by Bt are likely the primary acting components against pests. In the case of pathogens, however, it appears that both the Bt spores and proteins directly act against pathogens such as the fungus Botrytis cinerea. Bt Spores and produced proteins also both induce plant immunity. Understanding the different Bt mode of action mechanisms will help in developing cost-effective and safe plant protection strategies for enhancing food security. Taken together, our findings suggest that Bt could be used in broad-spectrum pest and disease management strategies. Pending validation in agricultural settings, Bt products on the market could have additional uses in sustainable pest management and plant growth promotion.

Management of root-knot nematode Meloidogyne incognita infesting turmeric (Curcuma longa) under coconut (Cocos nucifera) cropping system

Field experiments were conducted during 2018–19, 2019–20 and 2020–21 at ICAR-Central Plantation Crops Research Institute, Kasaragod, Kerala for assessment of biocontrol fungi for the management of root-knot nematode (RKN), Meloidogyne incognita damaging turmeric (Cucuma longa L.) (cv. IISR-Prathibha) under coconut (Cocos nucifera L.) cropping system. Treatments included talc-based formulations of Trichoderma harzianum (ICAR- Indian Institute of Spices Research (IISR), Kerala and ICAR-Central Plantation Crops Research Institute (CPCRI), Kerala isolates) and Pochonia chlamydosporia (ICAR-Indian Institute of Spices Research, Kerala isolate), neem cake, marigold and carbosulfan 25 ec (standard check). Talc-based formulations were applied at 50 g/bed, neem cake @1 kg/bed at pre-monsoon and post-monsoon, marigold @30 plants/bed compared with untreated and standard check carbosulfan 25 ec @5 litre/bed at pre-monsoon and post-monsoon against M. incognita. Maximum reduction of RKN in the soil, as well as root, was achieved by either P. chlamydosporia (74 and 86%, respectively) or carbosulfan (67 and 87%, respectively) over the control. A number of the tillers (3.75/plant) for P. chlamydosporia and (3.23/ plant) for carbosulfan were recorded more in comparison to control (1.42/plant). The findings demonstrated that P. chlamydosporia (ICAR-Indian Institute of Spices Research) is a promising alternative to synthetic nematicides for the management of M. incognita due to its high antagonistic and good plant growth promotion activities. However, large scale field trials on these promising fungal biocontrol agents can be considered for evaluation in relation to the management of RKN under field conditions for confirmation.

Statistical optimized production of Phytase from Hanseniaspora guilliermondii S1 and studies on purification, homology modelling and growth promotion effect

This investigation was performed to obtain a promising phytase enzyme producing yeast. In this regard, the PSM was used to isolate the phytase-producing Hanseniaspora guilliermondii S1 (MG663578) from sugarcane juice. The SSF optimum conditions for phytase generation were optimized using (OVAT) one-variable-at-a-time strategy using both Box-Behnken design and shake flask method (g/100 ml: 0.05 yeast extract, 0.15 Peptone, 0.05 malt extract 0.50 dextrose, pH 5.8 and 28ᵒC). The protein model developed was shown to be adequate for phytase production (91% accuracy), with the greatest phytase productivity in shake flask with substrate jack fruit seed powder being 395 ± 0.43 U/ml compared to 365U/ml for the BBD projected value. Crude Phytase was partially purified with a protein recovery of 43%, revealing a molecular weight of 120 kDa. It had an enzyme kinetic value of Km 3.3 mM and a Vmax of 19.1 mol/min. The 3D structure of PhyS1 amino acid sequences (PhyS1. B99990002) was simulated using Modeler 9.23, and the validated result revealed that 86.7% were in the favored region by Ramachandran plot. The SAVES server verified the 3D PDB file as satisfactory, and the model (in.pdb format) was uploaded in the PMDB database with the accession number ID: PM0082974. At the lab level, Hanseniaspora guilliermondii S1 (MG663578) producing phytase exhibited successful plant growth promotion activity in Ragi - CO 19 (Eleusine coracana L.) and Rice -Navarai - IR 64 (Oryza sativa L.). As a result, a phytase-based formulation for sustainable agriculture must be developed and tested on a large scale in diverse geographical areas of agricultural lands to determine its effect and potential on plant development.

Pseudomonas sp. AMGC1 takes on rice blast: Broad-spectrum antimicrobial activity underpins plant growth and disease tolerance.

A diverse group of gram-negative bacteria called Pseudomonas have been extensively researched for their ability to promote plant growth and suppress pathogens. The aim of the study was to identify the strain AMGC1 as a biocontrol agent against rice blast disease and a plant growth-promoting agent. The activity of AMGC1 against phytopathogens and its plant growth promotion activity were tested in vitro. Molecular identification by 16S rRNA gene sequencing, detection of antifungal antibiotic genes, biochemical characterization and antibiotic resistance testing were performed. Moreover, an in-planta biocontrol experiment with a blast susceptible rice cultivar was conducted to assess the effectiveness in managing the disease. Thin-layer chromatography was used to verify the presence of antifungal compounds. The results showed that AMGC1 had strong antimicrobial activity and multiple plant growth promotion traits. The strain was identified as Pseudomonas sp. and it contained genes for phenazine-1-carboxamide, hydrogen cyanide, and 2-hexyl, 5-propyl resorcinol antifungals. In the in-planta suppression experiment, applying AMGC1 strain two days before pathogen inoculation reduced the disease severity by 28% and disease incidence by 29% compared to control. Applying AMGC1 two days after pathogen inoculation resulted in lower reductions in disease severity (17.10%) and disease incidence (18.5%). Two putative bioactive compounds, phenazine-1-carboxamide and 2-hexyl, 5-propyl resorcinol, were isolated and purified from the AMGC1 growth medium. AMGC1 showed varied carbohydrate utilization patterns and both resistance and susceptibility to different antibiotics. The strain had multiple features that enhance plant growth and resistance against various phytopathogens, making it a potential biocontrol agent for sustainable agriculture.

Waste-liquors generated during Handmade paper manufacture from cow dung as a potential source of biofertilizer

In India, cow dung is widely utilized to create formulations that serve as effective plant growth enhancers with antimicrobial properties. The cow dung-derived handmade paper manufacturing process produces two waste-liquor streams, a Raw Liquor (RL) produced through the dewatering of the cow-dung slurry and a Black Liquor (BL) produced during the soda pulping of dewatered cow dung. The present study explored the potential of these waste streams to be used as plant biofertilizers for germination and cultivation of Vigna radiata seeds (mung bean, IPM-02-03 variety). An in vitro assay for seed germination efficiency and a pot study for plant growth promotion (PGP) activity were used to assess this potential. The in vitro assay demonstrated that nutrient-rich RL, with its 100% seed germination efficiency (better than the 85.7% of tap water) was an effective biofertilizer for seed germination. In contrast, BL yielded poor seed germination efficiency. The pot study showed that water irrigation led to good seed germination, survival, plant rooting and shooting, but it was probably deprived of nutrients for inducing good grain yields. When water was replaced with RL, it was able to replicate the results, but with good grain yields. In contrast, BL produced poorer germination, seed survival and PGP results. The poor biofertilization efficiency of BL was most probably due to the nutrient losses and toxic chemicals produced in the harsh pulping process. The results showed that RL, though considered a waste stream, is sufficiently nutrient-rich to act as an effective biofertilizer for germinating mung bean seeds and promoting plant growth and grain yields.

Functional analysis and comparative genomics of Rahnella perminowiae S11P1 and Variovorax sp. S12S4, two plant growth-promoting rhizobacteria isolated from Crocus sativus L. (saffron) rhizosphere.

Rahnella perminowiae S11P1 and Variovorax sp. S12S4 are two plant growth-promoting rhizobacteria that were previously isolated from the rhizosphere of Crocus sativus L. (saffron), and have demonstrated interesting PGP activities and promising results when used as inoculants in field trials. To further elucidate the molecular mechanisms underlying their beneficial effects on plant growth, comprehensive genome mining of S11P1 and S12S4 and comparative genomic analysis with closely related strains were conducted. Functional annotation of the two strains predicted a large number of genes involved in auxin and siderophore production, nitrogen fixation, sulfur metabolism, organic acid biosynthesis, pyrroloquinoline quinone production, 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity, volatile organic compounds production, and polyamine biosynthesis. In addition, numerous genes implicated in plant-bacteria interactions, such as those involved in chemotaxis and quorum sensing, were predicted. Moreover, the two strains carried genes involved in bacterial fitness under abiotic stress conditions. Comparative genomic analysis revealed an open pan-genomic structure for the two strains. COG annotation showed that higher fractions of core and accessory genes were involved in the metabolism and transport of carbohydrates and amino acids, suggesting the metabolic versatility of the two strains as effective rhizosphere colonizers. Furthermore, this study reports the first comparison of Multilocus sequence analysis (MLSA) and core-based phylogenies of the Rahnella and Variovorax genera. The present study unveils the molecular mechanisms underlying plant growth promotion and biocontrol activity of S11P1 and S12S4, and provides a basis for their further biotechnological application in agriculture.

Comprehensive genomic analysis of Bacillus subtilis and Bacillus paralicheniformis associated with the pearl millet panicle reveals their antimicrobial potential against important plant pathogens

BackgroundPlant microbiome confers versatile functional roles to enhance survival fitness as well as productivity. In the present study two pearl millet panicle microbiome member species Bacillus subtilis PBs 12 and Bacillus paralicheniformis PBl 36 found to have beneficial traits including plant growth promotion and broad-spectrum antifungal activity towards taxonomically diverse plant pathogens. Understanding the genomes will assist in devising a bioformulation for crop protection while exploiting their beneficial functional roles.ResultsTwo potential firmicute species were isolated from pearl millet panicles. Morphological, biochemical, and molecular characterization revealed their identities as Bacillus subtilis PBs 12 and Bacillus paralicheniformis PBl 36. The seed priming assays revealed the ability of both species to enhance plant growth promotion and seedling vigour index. Invitro assays with PBs 12 and PBl 36 showed the antibiosis effect against taxonomically diverse plant pathogens (Magnaporthe grisea; Sclerotium rolfsii; Fusarium solani; Alternaria alternata; Ganoderma sp.) of crops and multipurpose tree species. The whole genome sequence analysis was performed to unveil the genetic potential of these bacteria for plant protection. The complete genomes of PBs 12 and PBl 36 consist of a single circular chromosome with a size of 4.02 and 4.33 Mb and 4,171 and 4,606 genes, with a G + C content of 43.68 and 45.83%, respectively. Comparative Average Nucleotide Identity (ANI) analysis revealed a close similarity of PBs 12 and PBl 36 with other beneficial strains of B. subtilis and B. paralicheniformis and found distant from B. altitudinis, B. amyloliquefaciens, and B. thuringiensis. Functional annotation revealed a majority of pathway classes of PBs 12 (30) and PBl 36 (29) involved in the biosynthesis of secondary metabolites, polyketides, and non-ribosomal peptides, followed by xenobiotic biodegradation and metabolism (21). Furthermore, 14 genomic regions of PBs 12 and 15 of PBl 36 associated with the synthesis of RiPP (Ribosomally synthesized and post-translationally modified peptides), terpenes, cyclic dipeptides (CDPs), type III polyketide synthases (T3PKSs), sactipeptides, lanthipeptides, siderophores, NRPS (Non-Ribosomal Peptide Synthetase), NRP-metallophone, etc. It was discovered that these areas contain between 25,458 and 33,000 secondary metabolite-coding MiBiG clusters which code for a wide range of products, such as antibiotics. The PCR-based screening for the presence of antimicrobial peptide (cyclic lipopeptide) genes in PBs 12 and 36 confirmed their broad-spectrum antifungal potential with the presence of spoVG, bacA, and srfAA AMP genes, which encode antimicrobial compounds such as subtilin, bacylisin, and surfactin.ConclusionThe combined in vitro studies and genome analysis highlighted the antifungal potential of pearl millet panicle-associated Bacillus subtilis PBs12 and Bacillus paralicheniformis PBl36. The genetic ability to synthesize several antimicrobial compounds indicated the industrial value of PBs 12 and PBl 36, which shed light on further studies to establish their action as a biostimulant for crop protection.

Cyanobacteria Based Nanoformulation of Biogenic CuO Nanoparticles for Plant Growth Promotion of Rice Under Hydroponics Conditions.

Synthesizing nanoparticles through a green synthesis approach is common nowadays. Cyanobacteria have attained great importance in the field of biosynthesis of nanoparticles as there is no use of toxic chemicals as reducing or capping agents for the synthesis of metal oxide nanoparticles. Micronutrient-based nano-formulations have become a topic of great interest in recent times due to their various advantageous properties and applications in agriculture. The current study aims to exploit the potential cyanobacterial strains isolated from different locations such as freshwater and soil ecosystems. The potential cyanobacterial isolates were screened based on their multiple plant growth promoting (PGP) attributes such as Indol acetic acid (IAA) production, siderophores, and phosphate solubilization. After the screening of cyanobacteria based on multiple PGP activities, the cyanobacterial strain was identified at the species level as Pseudanabaena foetida RJ1, based on microscopy and molecular characterization using 16S rRNA gene sequencing. The cyanobacterial biomass extract and cell-free extracts are utilized for the synthesis of CuO micronutrient Nanoparticles (NPs). The cyanobacterial strain Pseudanabaena foetida RJ1 possesses plant growth-promoting (PGP) attributes that provide reduction and capping for CuO NPs. The synthesized NPs were characterized and subjected to make a nano-formulation, utilizing the cyanobacteria-mediated CuO NPs along with low-cost zeolite as an adsorbent. The application of cyanobacterial biomass extract and cell-free extract provided an excellent comparative aspect in terms of micronutrient NP synthesis. The NPs in the form of formulations were applied to germinated paddy seeds (Pusa Basmati -1509) with varying concentrations (5, 10, 15mg/l). Effects of cyanobacteria based CuO NPs on hydroponically grown paddy crops were analyzed. The application of nano-formulations has shown a significant increase in plant growth promotion in rice plants under hydroponics conditions. There is no such type of comparative investigation reported earlier, and NPs of micronutrients can be utilized as a new economic nanofertilizer and can be applied to plants for their growth promotion.

Auxin production and plant growth promotion by Microbacterium albopurpureum sp. nov. from the rhizoplane of leafless Chiloschista parishii Seidenf. orchid.

The strains of the genus Microbacterium, with more than 150 species, inhabit diverse environments; plant-associated bacteria reveal their plant growth-promoting activities due to a number of beneficial characteristics. Through the performance of diverse techniques and methods, including isolation of a novel Microbacterium strain from the aerial roots of leafless epiphytic orchid, Chiloschista parishii Seidenf., its morphological and biochemical characterization, chemotaxonomy, phylogenetic and genome analysis, as well as bioassays and estimation of its auxin production capacity, a novel strain of ET2T is described. Despite that it shared 16S rRNA gene sequence similarity of 99.79% with Microbacterium kunmingense JXJ CY 27-2T, so they formed a monophyletic group on phylogenetic trees, the two strains showed clear divergence of their genome sequences. The average nucleotide identity (ANI), average amino acid identity (AAI) and digital DNA-DNA hybridization (dDDH) values of ET2T differed greatly from phylogenetically close JXJ CY 27-2T. Based on the differences being below the threshold for species similarity, together with the unique chemotaxonomic characteristics, strain ET2T represents a novel species of the genus Microbacterium. Several genes, putatively involved in auxin biosynthesis were predicted. This strain revealed obvious plant growth-promoting activities, including diazotrophy and biosynthesis of tryptophan-dependent auxins (indole-3-acetic and indole-3-pyruvic acids). Microbial auxins directly stimulated the rhizogenesis, so that the ET2T-inoculated seeds of wheat, cucumber and garden cress showed evident promotion in their growth and development, both under optimal and under cold stress conditions. Based on phenotypic, chemotypic and genotypic evidences, the strain ET2T belongs to the genus Microbacterium, order Micrococcales, class Actinomycetes, and it represents a novel species, for which the name Microbacterium albopurpureum sp. nov. is proposed, with strain ET2T (VKPM Ac-2212, VKM Ас-2998) as the type strain.

ACC-Deaminase producing Pseudomonas putida RT12 inoculation: A promising strategy for improving Brassica juncea tolerance to salinity stress

An important abiotic stressor that hinders plant growth, nutrient uptake, and global agricultural productivity is soil salinity. Among the different strategies to overcome the issue of salinity in agriculture sector, plant growth-promoting rhizobacteria (PGPR) have gained recognition as promising beneficial microbes that can improve plants’ response to biotic and abiotic stressors. The salinity tolerance and traits that promote plant growth of eight PGPR strains (RT1, RT2, RT3, RT4, RT5, RT7, and RT12) were evaluated in this study. During screening, one strain, RT12, had the highest plant growth-promoting activity and salt tolerance in the group. The strain when subjected to NaCl stress showed quantitative ACC-deaminase activity, in the presence of NaCl at various concentrations, demonstrating extraordinary tolerance to salt stress by withstanding doses of up to 3M NaCl. In order to further investigate the effects of salt stress on Brassica juncea (mustard), RT12, which was identified as Pseudomonas putida using 16s RNA sequencing, was inoculated. Two salt treatments (100 and 150 mM) were applied to the mustard variety ‘Mingora’ in a greenhouse. The results revealed that through ACC utilization, PGPR directly induced plant growth in salt-stressed mustard plants by lowering excess ethylene production. All plant parameters were negatively impacted by an increase in NaCl concentration in uninoculated plants. However, P. putida RT12 inoculation enhanced all growth parameters, antioxidant production, total soluble sugar (TSS), total protein (TP), proline, relative water content (RWC), chlorophyll contents, and nutrient uptake in salt-treated plants. The inoculation with P. putida also caused a marked decline in Na+ uptake and an increase in K+ uptake in the shoot. By maintaining a greater K+/Na+ ratio in the tissues of RT12-inoculated plants compared to controls, this change in ion uptake helped to maintain nutritional balance of the plants. The findings suggest that inoculating plants with ACC deaminase-producing PGPR, such as P. putida RT12, may boost growth and stress resistance.

Emerging nitrogen-fixing cyanobacteria for sustainable cotton cultivation

Amid growing environmental concerns and the imperative for sustainable agricultural practices, this study examines the potential of nitrogen-fixing cyanobacteria as biofertilizers, particularly in cotton cultivation. The reliance on synthetic nitrogen fertilizers (SNFs), prevalent in modern agriculture, poses significant environmental challenges, including greenhouse gas emissions and water system contamination. This research aims to shift this paradigm by exploring the capacity of cyanobacteria as a natural and sustainable alternative. Utilizing advanced metabarcoding methods to analyze the 16S rRNA gene, we conducted a comprehensive assessment of soil bacterial communities within cotton fields. This study focused on evaluating the diversity, structure, taxonomic composition, and potential functional characteristics of these communities. Emphasis was placed on the isolation of native N2-fixing cyanobacteria strains rom cotton soils, and their subsequent effects on cotton growth. Results from our study demonstrate significant plant growth-promoting (PGP) activities, measured as N2 fixation, production of Phytohormones, Fe solubilization and biofertilization potential of five isolated cyanobacterial strains, underscoring their efficacy in cotton. These findings suggest a viable pathway for replacing chemical-synthetic nitrogen fertilizers with natural, organic alternatives. The reintegration of these beneficial species into agricultural ecosystems can enhance crop growth while fostering a balanced microbial environment, thus contributing to the broader goals of global sustainable agriculture.