Phosphate Solubilization Research Articles

Arsenic Stress Mitigation Using a Novel Plant Growth-Promoting Bacterial Strain Bacillus mycoides NR5 in Spinach Plant (Spinacia oleracea L.).

Present study aimed to identify arsenic (As)-resistant bacterial strains that can be used to mitigate arsenic stress. A bacterium Bacillus mycoides NR5 having As tolerance limit of 1100 mg L-1 was isolated from Nag River, Maharashtra, India. It was also equipped with plant growth-promoting (PGP) attributes like phosphate solubilization, siderophores, ammonia, and nitrate reduction, with added antibiotic tolerance. Furthermore, scanning electron microscopy (SEM) and transmission electron micrograph (TEM) suggested biosorption as possible mechanisms of arsenic tolerance. A strong peak in FTIR spectra at 3379.0 corresponding to amine in As-treated NR5 also indicated metal interaction with cell surface protein. Amplification of arsenic reductase gene in NR5 further suggested intracellular transformation of As speciation. Moreover, As tolerance capability of NR5 was shown in spinach plants in which the bacterium effectively mitigated 25 ppm As by producing defense-related proline molecules. Evidence from SEM, TEM, and FTIR, concluded biosorption possibly the primary mechanism of As tolerance in NR5 along with the transformation of arsenic. B. mycoides NR5 with PGP attributes, high As tolerance, and antibiotic resistance mediated enhanced As tolerance in spinach plants advocated that the strain can be a better choice for As bioremediation in contaminated agricultural soil and water.

Isolation and characterization of salt-stress-tolerant rhizosphere soil bacteria and their effects on plant growth-promoting properties

PGPR has a higher potential impact on agricultural crops. It enhances plant growth and development in a variety of adverse environmental conditions, including biotic and abiotic stresses. The PGPR is commercially vital since it is more efficient, safe for the environment, and beneficial to the economy. Nowadays, salt stress has an impact on the agricultural ecosystem. Salt-tolerant PGPR can directly stimulate plant growth and development by producing a variety of metabolites and phytohormones. The current study looked at the isolation of salt-tolerant bacterial species and their ability to stimulate plant development. Four bacterial species were chosen for their better salt stress tolerance (0–5%). They were identified by 16S rRNA sequencing: Solibacillus silvestris BR1, Peribacillus frigoritolerans BR2, Paenibacillus taichungensis CR1, and Solibacillus isronensis CR2. These strains were positive production of indole acetic acid with varying incubation periods (19.66 ± 1.528 to 646.111 ± 8.058 µg/mL), salt stress (ranging from 29.556 ± 1.171 to 147.8111 ± 2.086 µg/mL), phosphate solubilization (0.145 ± 0.011 to 0.921 ± 0.007 µg/mL), ammonium production (0.299 ± 0.047 to 1.202 ± 0.142 µg/mL), HCN production (0.308 ± 0.051 to 4.269 ± 0.069 µg/mL), and siderophore production (0.190 ± 0.064 to 1.543 ± 0.108 µg/mL) for control strains were used without salt stress. The production level was expressed using a standard curve containing various standards.

Jivamrit as a Sustainable Approach: A Review of Natural Farming and Future Agriculture.

Green Revolution aims to boost food production and feed millions of Indians, but it also has negative effects on agriculture and society's health. Natural manures like cow dung and cow urine can counteract the adverse effects of inorganic fertilizer on soil along with improving physicochemical qualities, maintaining the soil quality, and increasing crop output. Zero Budget Natural Farming (ZBNF) formulations like Jivamrit promote soil health and microbial activities and are an excellent source of macronutrients, other micronutrients needed for plant growth, plus adds beneficial microbes, nitrogen (N2), phosphorus (P), potassium (K), and natural carbon (C). Further, conventional agricultural methods, like monocropping and heavy tillage, can damage soil bacteria which contributes to sustainable agriculture through nitrogen fixation, siderophore synthesis and nutrient absorption. A sustainable agricultural system is resource-efficient, socially and commercially competitive, ecologically sound, and supportive of society. Jivamrit, a natural organic manure, is gaining interest due to concerns about the sustainability of input-intensive agriculture systems. It promotes crop growth, quality, and yield, enhances soil pH, population, and activity of beneficial microorganisms, and helps with nitrogen fixation, phosphate solubili-zation, and easy decomposition. Long-term use of Jivamrit, may disrupt soil microbial balance, may leading to overpopulation of certain species. The current review on the Jivamrit emphasizes on the biological and chemical characterization and its significance to the agriculture.

Antibiotics Resistance and PGPR Traits of Endophytic Bacteria Isolated in Arid Region of Morocco

This study aimed to characterize endophytic bacteria isolated from legume nodules and roots in the rhizosphere soils of Acacia trees in Morocco’s arid regions. The focus was on identifying bacterial strains with plant growth-promoting rhizobacteria (PGPR) traits and antibiotic resistance, which could enhance legume productivity under various abiotic stresses. Autochthonous legumes were used to harbor the endophytic bacteria, including chickpea (Cicer arietinum), faba bean (Vicia faba), lentil (Lens culinaris), and common bean (Phaseolus vulgaris). In a previous study, seventy-two isolates were obtained, and molecular characterization grouped them into twenty-two bacterial isolates. These twenty-two bacterial isolates were then further analyzed for their antibiotic resistance and key PGPR traits, such as phosphate solubilization, indole-3-acetic acid (IAA) production, and siderophore production. The results revealed that 86.36% of the isolates were resistant to erythromycin, 45.45% to ciprofloxacin, 22.73% to ampicillin-sulbactam, and 9.09% to tetracycline, with ciprofloxacin and tetracycline being the most effective. All isolates produced IAA, with HN51 and PN105 exhibiting the highest production at 6 µg of IAA per mg of protein. The other isolates showed varying levels of IAA production, ranging from moderate to low. Siderophore production, assessed using CAS medium, indicated that the strains PN121, LR142, LNR146, and HR26 exhibited high production, while the rest demonstrated moderate to low capacities. Additionally, 18.2% of the isolates demonstrated phosphate solubilization on YED-P medium, with PR135 and LNR135 being the most efficient, achieving solubilization indices of 2.14 and 2.13 cm, respectively. LR142 and LNR146 showed a moderate solubilization efficiency. Overall, these findings indicate that these isolated endophytic bacteria possess significant potential as biofertilizers, owing to their antibiotic resistance, IAA production, siderophore production, and phosphate solubilization abilities. These characteristics position them as promising candidates for enhancing legume growth under abiotic stress and contributing to sustainable agriculture in arid regions.

Characterization of Plant Growth Promoting Rhizobacteria and Their Benefits on Soybean Growth

Background: Soybean is the most important legume in the world and its seeds contains 40% protein and 20% oil. In recent years, more attention has been paid to the use of plant growth-promoting (PGP) rhizobacteria as a biofertilizer alternative to chemical fertilizers, which may pose risks to the environment. The rhizobia inoculation of soybean is a sustainable practice to induce atmospheric nitrogen fixation and subsequently improve crop productivity and soil fertility. Methods: In this study, 19 indigenous rhizobia isolated from soybean were tested in vitro for their plant growth-promoting properties (PGPR), while genotypic characterization included sequencing of the 16S rRNA gene. Result: Morphological characterisation has shown that all of the isolates were rod-shaped gram negative bacteria. The sequencing has shown that 12 out of 19 isolates belong to the genus Pseudomonas, four of which belong to P. fluorescens species. Isolates which belong to the Pseudomonas genus have shown the highest ability of indole-3-acetic acid synthesis, phosphorous solubilization and along with isolates SGN6, SGN7 and SGS4 (Sphingomonas sanguinis) potassium solubilisation too. All the isolates from Pseudomonas genus as well as those belonging to B. japonicum species have shown the protease synthesis abilities while amylase synthesis abilities was observed only in the isolate SAK2 (P. chlororaphis). The most efficient strains in in vitro biological nitrogen fixation assay belong to Pseudomonas and Rhizobium genera. Most of the isolates were positive to the organic acid production while all of them have shown the ability of the exopolysaccharide production.

Selection and Effect of Plant Growth-Promoting Bacteria on Pine Seedlings (Pinus montezumae and Pinus patula).

Forest cover is deteriorating rapidly due to anthropogenic causes, making its restoration urgent. Plant growth-promoting bacteria (PGPB) could offer a viable solution to ensure successful reforestation efforts. This study aimed to select bacterial strains with mechanisms that promote plant growth and enhance seedling development. The bacterial strains used in this study were isolated from the rhizosphere and endophyte regions of Pinus montezumae Lamb. and Pinus patula Schl. et Cham., two Mexican conifer species commonly used for reforestation purposes. Sixteen bacterial strains were selected for their ability to produce auxins, chitinase, and siderophores, perform nitrogen fixation, and solubilize inorganic phosphates; they also harbored genes encoding antimicrobial production and ACC deaminase. The adhesion to seeds, germination rate, and seedling response of P. montezumae and P. patula were performed following inoculation with 10 bacterial strains exhibiting high plant growth-promoting potential. Some strains demonstrated the capacity to enhance seedling growth. The selected strains were taxonomically characterized and belonged to the genus Serratia, Buttiauxella, and Bacillus. These strains exhibited at least two mechanisms of action, including the production of indole-3-acetic acid, biological nitrogen fixation, and phosphate solubilization, and could serve as potential alternatives for the reforestation of affected areas.

Isolation and characterization of Pantoea ananatis and P. agglomerans in quinoa: P. ananatis as a potential fungal biocontroller and plant growth promoter.

Chenopodium quinoa, globally recognized as quinoa, stands out as one of the cereals with the highest nutritional value native to the Americas. It is cultivated in the Andes Mountain range, and Colombia is no exception, with the Boyacá department emerging as a significant quinoa-producing region. The quinoa ecosystem harbors a rich array of microorganisms within its rhizosphere. In this current study, nitrogen-fixing and phosphate-solubilizing isolates AM-0261 (Pantoea ananatis) and AM-0263 (Pantoea agglomerans) were sourced from rhizospheric soil samples of quinoa. These isolates were subjected to biochemical characterization and identification through PCR analysis and Sanger sequencing targeting a partial sequence of the 16s region of the rRNA. To assess their potential as plant growth-promoting rhizobacteria (PGPR), taking into consideration that P. ananatis is an IAA producer, greenhouse-based bioassays were conducted using seedlings. Additionally, dual culture assays were employed to showcase their antagonistic capabilities against primary beneficial and phytopathogenic fungi associated with quinoa cultivation in the region. The results underscore the remarkable potential of P. ananatis as a PGPR and a biocontrol agent against quinoa's phytopathogenic fungi. This study represents the pioneering exploration of the interaction between these two bacterial strains with quinoa rhizosphere tissue. In addition, the isolate of P. annatis (AM-0261) stands out, which presents phosphate solubilization capacity, nitrogen fixation, antagonistic capacity, and IAA production, characteristics that make it a promising strain for its use for the management of diseases of fungal origin, and in the future, it could be useful in reducing the use of chemical fertilizers.

The role of proton excreted by Advenella kashmirensis DF12 during ammonium assimilation in phosphate solubilization.

Phosphate-solubilizing bacteria (PSB) can solubilize soil fixed phosphorus (P) to plant available forms. In previous studies, the mechanisms of inorganic phosphate solubilization by PSB mostly focused on the acidolysis of organic acids. Here we screened a highly efficient PSB, Advenella kashmirensis DF12, with the maximum P solubilization of 590 mg L- 1 at 6 days. In addition to its P solubilizing ability, DF12 also showed a tolerance to pH from 5 to 10 and a nitrogen fixation potential. The multiple functions of DF12 and its wide adaptability to various environmental conditions make it a promising biofertilizer candidate. The combined analysis of extracellular metabolites and intracellular metabolome data revealed that the production of organic acid (mainly gluconic acid) is not the only mechanism of P solubilized by DF12, the solubilized P content was not correlated with the gluconic acid concentration but was in a highly significant positive correlation with proton concentration, extrusion of proton during NH4+ assimilation plays a key role in phosphate solubilization. Moreover, the contribution of NH4+ assimilation to phosphorus solubilization is generally present in PSB. Therefore, we proposed that applying ammonium fertilizer in P-deficient soil is more appropriate, it can not only supplement nitrogen fertilizer, but also enhance P use efficiency, which contributes to worldwide fertilizer use reduction and efficiency improvement.

Halophilic Phosphate-Solubilizing Microbes (Priestia megaterium and Bacillus velezensis) Isolated from Arabian Sea Seamount Sediments for Plant Growth Promotion.

Arabian Sea is a highly productive Ocean owing to deep upwelling with reports on phosphorus cycling in ocean sediments. In this study, microbes from sea mounts of the Arabian Sea at varying depths (400m, 900m) were screened to isolate and characterize phosphate-solubilizing bacteria (PSB) with plant growth-promoting properties. Out of the seven morphologically different PSBs, two bacterial strains with maximum phosphate solubilization index were identified as Priestia megaterium (H1) and Bacillus velezensis (H2) based on biochemical and molecular characteristics. Different factors influencing phosphatase production were optimized, which showed maximum solubilization at temperature of 30°C (97.5μg/mL), glucose as best carbon source (70µg/mL), 1-M NaCl (114.1µg/mL), and pH 8 (134.3µg/mL) indicating their halophilic and alkaliphilic characteristics. Alkaline phosphatase enzyme was extracted and partially purified from both PSBs wherein H2 strains showed greater specific activity (24.83 U/mg). Metabolomics studies through HPLC revealed maximum production of gluconic acid (483.75mg/L) in addition to lactic, oxalic, acetic, and succinic acid during solubilization. Biopriming effect of PSBs on tomato seed germination showed high germination index (80%) in consortia of both isolates which was also validated through root colonization by SEM analysis. Further studies using pot assay experiments also showed comparable results in marine PSB consortia with positive control (Phosphobacteria) for plant growth attributes including root height and weight. These findings suggest that the halophilic PSB strains from marine sediments could be used as potential bio-inoculants to enhance plant growth and combat saline stress for sustainable Agriculture.

Characterization of Bacillus pacificus G124 and Its Promoting Role in Plant Growth and Drought Tolerance.

Drought represents a major environmental threat to global agricultural productivity. Employing plant growth-promoting rhizobacteria (PGPR) offers a promising strategy to enhance plant growth and resilience under drought stress. In this study, the strain G124, isolated from the arid region of Qinghai, was characterized at the molecular level, and its ability to enhance plant drought tolerance was validated through pot experiments. The findings revealed that the strain G124 belongs to Bacillus pacificus, with a 99.93% sequence similarity with B. pacificus EB422 and clustered within the same clade. Further analysis indicated that the strain G124 demonstrated a variety of growth-promoting characteristics, including siderophore production, phosphate solubilization, and the synthesis of indole-3-acetic acid (IAA), among others. Moreover, inoculation with B. pacificus G124 resulted in significant enhancements in plant height, leaf area, chlorophyll content, relative water content, and root development in both Arabidopsis thaliana and Medicago sativa seedlings under drought conditions. Additionally, G124 boosted antioxidant enzyme activities and osmolyte accumulation, while reducing malondialdehyde (MDA) and reactive oxygen species (ROS) levels in M. sativa seedlings exposed to drought. These findings suggest that B. pacificus G124 holds significant promise for enhancing plant drought tolerance and could be effectively utilized in crop management strategies under arid conditions.

Exploring Plant Growth-Promoting Traits of Endophytic Fungi Isolated from Ligusticum chuanxiong Hort and Their Interaction in Plant Growth and Development.

Endophytic fungi inhabit various plant tissues and organs without inducing evident disease symptoms. They can contribute positively to the growth of plants, bolster plants resilience to environmental and biological stresses, and facilitate the accumulation of secondary metabolites. These microbial resources possess significant developmental and utilization value in various applications. Hence, this study focused on exploring the plant growth-promoting (PGP) traits of 14 endophytic fungi from Ligusticum chuanxiong Hort (CX) and elucidating the effects and mechanisms that facilitate plant growth. According to PGP activity evaluation, the majority of strains demonstrated the capacity to produce IAA (78.57%), siderophores (50.00%), ammonia (35.71%), potassium solubilization (21.43%), nitrogen fixation (57.14%), and phosphate solubilization (42.86%). Further investigations indicated that the levels of IAA ranged from 13.05 to 301.43 μg/mL, whereas the soluble phosphorus levels ranged from 47.32 to 125.95 μg/mL. In cocultivation assays, it was indicated that Fusarium sp. YMY5, Colletotrichum sp. YMY6, Alternaria sp. ZZ10 and Fusarium sp. ZZ13 had a certain promoting effect on lateral root number and fresh weight of tobacco. Furthermore, ZZ10 and ZZ13 significantly enhanced the germination potential, germination index, and vigor index of tobacco seeds. The subsequent potted trials demonstrated that the four endophytic fungi exhibited an enhancement to growth parameters of tobacco to a certain extent. ZZ10 and ZZ13 treatment had the best promotion effect. Inoculation with YMY5 increased the chlorophyll a and total chlorophyll content. ZZ10 and ZZ13 treatment remarkably increased the net photosynthetic rate, soluble sugars and soluble protein content, catalase and peroxidase activities, and lowered malondialdehyde content in tobacco leaves. In addition, YMY5 remarkably elevated superoxide dismutase activities. ZZ13 upregulated the expression of growth-related gene. Among them, ZZ13 had a better growth-promoting effect. In conclusion, these endophytic fungi possessing multi-trait characteristics and the capacity to enhance plant growth exhibit promising potential as biofertilizers or plant growth regulators.

Exploring the Potential of Bacterial Endophytes in Plant Disease Management.

Endophytic bacteria live in the internal tissues of plants, forming symbiotic, mutualistic, commensalistic and trophobiotic relationships. Some are spread via seeds after sprouting from the rhizosphere or phyllosphere. These bacteria capable of promoting plant growth and impart biotic stress by synthesing plant growth hormones, ACC deaminase, organic acids and siderophore. Endophytes aid in phytoremediation by removing soil contaminants and boosting soil fertility via phosphate solubilization and nitrogen fixation. The endophytic microbes are becoming increasingly popular in biotechnological applications which supports sustainable growth of non-food crops for biomass and biofuel. They offer valuable natural materials which is used in medicine, agriculture and industry. Bacterial endophytes are endowed with the enormous potential in the biological treatment of plant pathogens and considered as the superior alternative to synthetic fungicides. The review emphasizes benefits of bacterial endophytes in promoting plant growth and prospects of agricultural applications viz., increasing crop yield under biotic stress condition and their mode of action towards plant diseases. It also summarises the diverse and vital role of endophytes in agroecosystems as well as insights for sustainable agriculture and crop resilience.

Diversity and Bioactivity of Endophytic Actinobacteria Associated with the Roots of Artemisia herba-alba Asso from Algeria.

The isolation of endophytic actinobacteria from the roots of wild populations of Artemisia herba-alba Asso, a medicinal plant collected from the arid lands of Algeria, is reported for the first time. Forty-five actinobacterial isolates were identified by molecular analysis and in vitro evaluated for antimicrobial activity and plant growth-promoting (PGP) abilities (1-Aminocyclopropane-1-carboxylic acid (ACC) deaminase activity, nitrogen fixation, phosphate and potassium solubilization, ammonia, and siderophores production). The phylogenetic relationships based on 16S rRNA gene sequences show that the genus Nocardioides (n = 23) was dominant in the sampled localities. The remaining actinobacterial isolates were identified as Promicromonospora (n = 11), Streptomyces (n = 6), Micromonopora (n = 3), and Saccharothrix (n = 2). Only six (13.33%) strains (five Streptomyces and one Saccharothrix species) were antagonistic in vitro against at least one or more indicator microorganisms. The antimicrobial activity of actinobacterial strains targeted mainly Gram-positive bacteria. The results demonstrate that more than 73% of the isolated strains had ACC deaminase activity, could fix atmospheric nitrogen and were producers of ammonia and siderophores. However, only one (2.22%) strain named Saccharothrix sp. BT79 could solubilize phosphorus and potassium. Overall, many strains exhibited a broad spectrum of PGP abilities. Thus, A. herba-alba provides a source of endophytic actinobacteria that should be explored for their potential biological activities.

Genetic Diversity and Functional Potential of Streptomyces spp. Isolated from Pachmarhi Biosphere Reserve, India.

Streptomyces is a diverse genus, well known for producing a wide array of metabolites that have significant industrial utilization. The present study investigates the genetic and functional diversity of Streptomyces spp. isolated from the Pachmarhi Biosphere Reserve (PBR), India, an unexplored site. The 16S rRNA gene sequencing and analysis revealed 96 isolates belonging to 40 different species indicating a substantial phylogenetic diversity. The strains were clustered into two groups: a major cluster with 94 strains and a small cluster with two strains. BOX- PCR analyses revealed an incredible genetic diversity existing among the strains of Streptomyces spp. in PBR. The analyses revealed the intra-species diversity and inter-species closeness within the genus Streptomyces in the study area. Qualitative screening for enzyme production has shown that 53, 42, 41, 11, and 54 strains tested positive for CMCase, xylanase, amylase, pectinase, and β-glucosidase, respectively. Additionally, 54 strains tested positive for PHB production. The strains were assayed quantitatively for the production of CMCase, xylanase, amylase, and pectinase. Streptomyces sp. MP9-2, Streptomyces sp. MP10-11, Streptomyces sp. MP10-18, and Streptomyces sp. MP10-6 recorded maximum CMCase (0.604 U/mL), xylanase (0.553 U/mL), amylase (1.714 U/mL), and pectinase (13.15 U/mL) activities, respectively. Furthermore, several strains demonstrated plant growth-promoting traits, viz. zinc and phosphate solubilization and production of ammonia, HCN (hydrogen cyanide), and IAA (Indole acetic acid), and nitrogen fixation. Fifty strains showed antifungal activity against Fusarium oxysporum f. sp. lycopersici with inhibitions ranging from 7.5 to 47.5%. Current findings underscore the ecological and biotechnological significance of Streptomyces spp. in the unexplored habitat of PBR.

A study on the potential of endophytic bacteria to promote plant growth: uses in agriculture and future directions

The escalating demand for chemical-free fertilizers in agriculture stems from the adverse impacts associated with chemical fertilizers on both human and animal health, as well as environmental pollution. To address this concern, plant-based microorganisms emerge as a promising solution for the development of environmentally sustainable biofertilizers. Among these microorganisms, endophytic bacteria, residing within plant tissues without causing harm to the host plant, exhibit exceptional attributes conducive to plant growth promotion. Notably, these bacteria demonstrate the production of phytohormones, ammonia, phosphate solubilization, and nitrogen fixation capabilities. Additionally, endophytic bacteria showcase the synthesis of hydrolytic enzymes, the production of siderophores, and antimicrobial activity against pathogens. Such characteristics contribute significantly to the robust growth and development of host plants, fostering tolerance to environmental stresses. This manuscript aims to comprehensively review the plant growth promotion activities of endophytic bacteria, elucidating their diversity and isolation from various plants. Furthermore, it explores the potential future directions in this burgeoning field of research, envisioning the development of endophytic bacterial strains capable of replacing traditional chemical fertilizers. Future research endeavors hold the promise of uncovering novel and effective endophytic bacterial strains, heralding a sustainable paradigm shift in the realm of agricultural fertilization.

Response of Biofertilizer and Molybdenum on Growth and Yield of Barley (Hordeum vulgare L.)

The field experiment was conducted during rabi season, 2023-24 at research farm, Vivekananda Global University, Jaipur. The experiment was layout in Randomized Block Design (RBD). The treatments consisted of biofertilizers like Azotobacter and Phosphate Solubilizing Bacteria (PSB) and three level of Molybdenum (400, 600 and 800 ppm) and control. The soil in the experimental area was sandy loam with pH (7.81), Organic Carbon (0.21%), Available N (132.5 kg/ha), Available P (21.13 kg/ha) and Available K (203.24 kg/ha). Seed rate is 100 kg/ha. The application of biofertilizers + PSB + 800 ppm Mo significantly increased the Plant height (110.46 cm), Dry matter accumulation (542.54 g/m2), No. of tillers/ running row meter (93.51), Number of effective tillers m-2 (199.86), Number of grains spike-1 (53.60), Grain yield (3450 kg/ha) and Straw Yield (6562 kg/ha) of barley over the control.

Ecological practices increase soil fertility and microbial diversity under intensive farming

Intensive farming offers a potential solution to feed the growing population due to its high productivity. Conventional management (CO) based on inorganic fertilization practices degrades soil quality, but restorative practices including ecological intensification (EI) and organic management results in maintaining soil quality without compromising productivity. In this paper, two different management systems were evaluated: CO, based on inorganic fertilization, and EI, focused on providing organic nutrients to soils to support crops.EI increased soil fertility, together with higher alpha diversity indices, more differentially abundant amplicon sequence variant (ASVs) (247 EI vs. 165 CO) and indicator taxa (60 EI vs. 32 CO). Distinct bacterial taxa were associated with the different management systems, revealing their roles in soil processes and nutrient availability. In the CO treatment, indicator genera such as Nitrospira and Desulfarculaceae were linked to N fertilization and nitrite oxidation, while RB41 was associated with phosphorus availability. Ammoniphilus, PAUC26f, and BSV26 were also indicators of CO management. Conversely, EI treatment promoted bacteria involved in organic matter decomposition and nutrient cycling, such as Halomonas, Chryseolinea and Rhodobacteraceae. Gemmatimonas, Steroidobacter, Altererythrobacter, Acidibacter and Anseongella contribute to carbon and nitrogen cycling. Burkholderiaceae and Rhodopirellula play roles in phosphate solubilization and organic P mineralization, respectively. Numerous taxa with plant growth-promoting (PGP) attributes, such as BIrii41, Pseudomonas, and Lysobacter, were also identified as indicators of the EI treatment.EI associated bacteria were positively correlated with soil organic carbon contents, nitrates, and exchangeable bases, while negatively correlated with CO bacteria. A distance-based multivariate multiple regression (DistLM) demonstrated a strong relationship (r2 = 0.78) between soil physicochemical variables and bacterial community structure, with SOC explaining the most variations in the model. Other significant parameters included potassium (K), electrical conductivity (EC), and nitrates. The results suggest that EI promotes more sustainable soils in terms of fertility and microbial diversity.

Bioactive Potential of Actinobacteria Strains Isolated from the Rhizosphere of Lavender, Lemon Balm, and Oregano

The objective of this study was to isolate and characterize actinobacteria from the rhizosphere of medicinal and aromatic plants, specifically lavender (Lavandula angustifolia Mill.), lemon balm (Melissa officinalis L.), and oregano (Origanum vulgare L.). Rhizospheric soil samples revealed a high abundance of culturable actinobacteria (6.97–7.23 log10 CFU/g). Six isolates were selected for their promising enzymatic activities (lignin peroxidase, carboxymethyl cellulase) and antimicrobial properties. Isolates M345 and M162 exhibited the highest cellulase activity indices (3.19 ± 0.71 and 2.54 ± 0.22, respectively), with five isolates producing lignin peroxidase. These actinobacteria also demonstrated plant growth-promoting traits such as phosphate solubilization and nitrogen fixation, along with strong antimicrobial activity against Gram-negative bacteria and phytopathogenic fungi. Additionally, they significantly enhanced maize seed germination, increasing the vigor index from 4283.33 ± 1264.37 to 6248.28 ± 1661.94 compared to that of the control. These results indicate that the isolated actinobacteria strains hold potential as microbial inoculants for sustainable agriculture, contributing to soil health, plant growth, and pathogen management.

Effects of phosphate-solubilizing bacteria Aspergillus flavus AF-LRH1 on promoting phosphorus solubilization, wheat growth and soil heavy metal remediation

Increasing nutrient supply level and eliminating pollution risk are essential to promote farmland soil use. In the soil-plant nutrition cycle, phosphorus is a limiting nutrient, toxic metals such as Cd and Pb are stress threats. Utilizing microorganisms as a bio-amendment could be a viable approach to enhance the cycling of soil phosphorus nutrients and immobilize Cd and Pb in the soil. This study involved the isolation of Aspergillus flavus AF-LRH1, a phosphate solubilizing fungal strain from soil. The strain exhibited the capacity to solubilize calcium phosphate, attaining a phosphorus concentration of 220.73 mg L−1 in the medium. High performance liquid chromatography analysis showed that AF-LRH1 produced a combination of organic acids (tartaric acid 260.7 mg L−1, fumaric acid 0.8 mg L−1, citric acid 911.9 mg L−1) to dissolve Ca3(PO4)2 by providing H+ ions. AF-LRH1 also utilizes NH4+ for the biosynthesis of amino acids and releases protons, which facilitate the dissolution of insoluble Ca3(PO4)2 and calcium phytate. Through these processes, calcium phosphate is partly converted into hydroxyapatite because of biological solubilization. AF-LRH1 strain showed the capability to recover phosphorus from various types of sludge-based solid residue by increasing the solubility of insoluble phosphate compounds for plant nutrient supply. In addition, the combining addition of AF-LRH1 strain and phosphate-containing amendments (calcium phosphate, sludge ash and biochar) benefited the decontamination of Pb and Cd contaminated soil. This finding confirmed the AF-LRH1 could be a promising environmental-friendly biofertilizer suitable for agricultural applications and bioremediation of heavy metal contaminated soil.

Interactions between arbuscular mycorrhizal fungi and phosphate-soluble bacteria affect ginsenoside compositions by modulating the C:N:P stoichiometry in Panax ginseng.

The biomass production as well as the accumulation of secondary metabolites of plant is highly determined by the absorption of nutritional elements, in particular nitrogen (N) and phosphorus (P). Arbuscular mycorrhizal fungi (AMF) can absorb soluble P and transport it to plants, while phosphate solubilizing bacteria (PSB) can increase the content of solubilizing P in soil. Previous studies have identified the effects of either AMF or PSB inoculation on altering plant C:N:P stoichiometry, whether AMF interact with PSB in promoting plant growth and changing elemental concentration and composition of secondary metabolites by altering plant C:N:P stoichiometry remains ambiguous. In this study, we investigated the effects of inoculation of AMF, PSB, and their co-inoculation AMP (AMF and PSB) on the biomass growth, the C:N:P stoichiometry, the core microorganisms of rhizosphere soil, and the ginsenoside compositions of ginseng (Panax ginseng). The results showed that compared to control or single inoculation of AMF or PSB, co-inoculation of AMF and PSB significantly increased the AMF colonization rate on ginseng roots, increased the biomass of both above and under-ground parts of ginseng. Similarly, co-inoculation of AMF and PSB substantially increased the concentrations of N and P, reduced the ratios of C:P and N:P in the above-ground part of ginseng. The co-inoculation of AMF and PSB also increased concentrations of total ginsenosides and altered the compositions of ginsenosides in both the above and under-ground parts of ginseng. Analysis the rhizosphere microorganism showed that the co-inoculation of AMF and PSB recruited distinct core microorganisms that differ from the control and treatments with single inoculation of AMF or PSB. Our results suggested that PSB inoculation enhanced the positive effect of AMF in improving the absorption of nutrimental elements, altered the C:N:P stoichiometry and, ginsenosides concentration and composition of ginseng, influenced the plant rhizosphere microbial community. These findings offer valuable insights into enhancing plant biomass production and promoting secondary metabolites by improving the plant-fungi-bacterial relationships.